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1.
J Physiol Pharmacol ; 69(1): 99-107, 2018 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-29769426

RESUMEN

Intracellular calcium concentration ([Ca2+]i) is often buffered by using the cell-permeant acetoxy-methylester form of the Ca2+ chelator BAPTA (BAPTA-AM) under experimental conditions. This study was designed to investigate the time-dependent actions of extracellularly applied BAPTA-AM on action potential duration (APD) in cardiac cells. Action potentials were recorded from enzymatically isolated canine ventricular myocytes with conventional sharp microelectrodes. The effect of BAPTA-AM on the rapid delayed rectifier K+ current (IKr) was studied using conventional voltage clamp and action potential voltage clamp techniques. APD was lengthened by 5 µM BAPTA-AM - but not by BAPTA - and shortened by the Ca2+ ionophore A23187 in a time-dependent manner. The APD-lengthening effect of BAPTA-AM was strongly suppressed in the presence of nisoldipine, and enhanced in the presence of BAY K8644, suggesting that a shift in the [Ca2+]i-dependent inactivation of L-type Ca2+ current may be an important underlying mechanism. However, in the presence of the IKr-blocker dofetilide or E-4031 APD was shortened rather than lengthened by BAPTA-AM. Similarly, the APD-lengthening effect of 100 nM dofetilide was halved by the pretreatment with BAPTA-AM. In line with these results, IKr was significantly reduced by extracellularly applied BAPTA-AM under both conventional voltage clamp and action potential voltage clamp conditions. This inhibition of IKr was partially reversible and was not related to the Ca2+ chelator effect BAPTA-AM. The possible mechanisms involved in the APD-modifying effects of BAPTA-AM are discussed. It is concluded that BAPTA-AM has to be applied carefully to control [Ca2+]i in whole cell systems because of its direct inhibitory action on IKr.


Asunto(s)
Potenciales de Acción/efectos de los fármacos , Quelantes del Calcio/farmacología , Calcio/metabolismo , Ácido Egtácico/análogos & derivados , Miocitos Cardíacos/efectos de los fármacos , Animales , Perros , Ácido Egtácico/farmacología , Femenino , Ventrículos Cardíacos/citología , Masculino , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/fisiología
2.
J Physiol Pharmacol ; 67(4): 483-489, 2016 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-27779469

RESUMEN

Omecamtiv mecarbil (OM) is a myosin activator agent recently developed for treatment of heart failure. Although its action on extending systolic ejection time and increasing left ventricular ejection fraction is well documented, no data is available regarding its possible side-effects on cardiac ion channels. Therefore, the present study was designed to investigate the effects of OM on action potential morphology and the underlying ion currents in isolated canine ventricular myocytes using sharp microelectrodes, conventional patch clamp, and action potential voltage clamp techniques. OM displayed a concentration-dependent action on action potential configuration: 1 µM OM had no effect, while action potential duration and phase-1 repolarization were reduced and the plateau potential was depressed progressively at higher concentrations (10 - 100 µM; P < 0.05 compared to control). Accordingly, OM (10 µM) decreased the density of the transient outward K+ current (Ito), the L-type Ca2+ current (ICa) and the rapid delayed rectifier K+ current (IKr), but failed to modify the inward rectifier K+ current (IK1). It is concluded, that although the therapeutic concentrations of OM are not likely to influence cardiac ion currents significantly, alterations of the major cardiac ion currents can be anticipated at concentrations above those clinically tolerated.


Asunto(s)
Miocitos Cardíacos/efectos de los fármacos , Urea/análogos & derivados , Potenciales de Acción/efectos de los fármacos , Animales , Perros , Femenino , Ventrículos Cardíacos/citología , Masculino , Miocitos Cardíacos/fisiología , Miosinas , Técnicas de Placa-Clamp , Urea/farmacología
3.
J Physiol Pharmacol ; 66(1): 73-81, 2015 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-25716967

RESUMEN

The aim of the present work was to study the influence of changes in intracellular calcium concentration ([Ca(2+)]i) on beat-to-beat variability (short term variability, SV) of action potential duration (APD) in isolated canine ventricular cardiomyocytes. Series of action potentials were recorded from enzymatically isolated canine ventricular cells using conventional microelectrode technique. Drug effects on SV were evaluated as relative SV changes determined by plotting the drug-induced changes in SV against corresponding changes in APD and comparing these data to the exponential SV-APD function obtained with inward and outward current injections. Exposure of myocytes to the Ca(2+) chelator BAPTA-AM (5 µM) decreased, while Ca(2+) ionophore A23187 (1 µM) increased the magnitude of relative SV. Both effects were primarily due to the concomitant changes in APD. Relative SV was reduced by BAPTA-AM under various experimental conditions including pretreatment with veratridine, BAY K8644, dofetilide or E-4031. Contribution of transient changes of [Ca(2+)]i due to Ca(2+) released from the sarcoplasmic reticulum (SR) was studied using 10 µM ryanodine and 1 µM cyclopiazonic acid: relative SV was reduced by both agents. Inhibition of the Na(+)-Ca(2+) exchanger by 1 µM SEA0400 increased relative SV. It is concluded that elevation of [Ca(2+)]i increases relative SV significantly. More importantly, Ca(2+) released from the SR is an important component of this effect.


Asunto(s)
Potenciales de Acción , Señalización del Calcio , Calcio/metabolismo , Frecuencia Cardíaca , Ventrículos Cardíacos/metabolismo , Miocitos Cardíacos/metabolismo , Potenciales de Acción/efectos de los fármacos , Animales , Agonistas de los Canales de Calcio/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Quelantes del Calcio/farmacología , Ionóforos de Calcio/farmacología , Señalización del Calcio/efectos de los fármacos , Perros , Femenino , Frecuencia Cardíaca/efectos de los fármacos , Ventrículos Cardíacos/citología , Ventrículos Cardíacos/efectos de los fármacos , Masculino , Miocitos Cardíacos/efectos de los fármacos , Retículo Sarcoplasmático/metabolismo , Intercambiador de Sodio-Calcio/metabolismo , Factores de Tiempo
4.
Curr Pharm Des ; 21(8): 1073-90, 2015.
Artículo en Inglés | MEDLINE | ID: mdl-25354179

RESUMEN

The cardiac late sodium current (INa,L) has been in the focus of research in the recent decade. The first reports on the sustained component of voltage activated sodium current date back to the seventies, but early studies interpreted this tiny current as a product of a few channels that fail to inactivate, having neither physiologic nor pathologic implications. Recently, the cardiac INa,L has emerged as a potentially major arrhythmogenic mechanism in various heart diseases, attracting the attention of clinicians and researchers. Research activity on INa,L has exponentially increased since Ranolazine, an FDA-approved antianginal drug was shown to successfully suppress cardiac arrhythmias by inhibiting INa,L. This review aims to summarize and discuss a series of papers focusing on the cardiac late sodium current and its regulation under physiological and pathological conditions. We will discuss critical evidences implicating INa,L as a potential target for treating myocardial dysfunction and cardiac arrhythmias.


Asunto(s)
Antiarrítmicos/farmacología , Arritmias Cardíacas/tratamiento farmacológico , Canales de Sodio/efectos de los fármacos , Animales , Antiarrítmicos/uso terapéutico , Arritmias Cardíacas/fisiopatología , Corazón/efectos de los fármacos , Corazón/fisiopatología , Humanos , Canales de Sodio/fisiología
5.
Br J Pharmacol ; 167(3): 599-611, 2012 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-22563726

RESUMEN

BACKGROUND AND PURPOSE: Although isoprenaline (ISO) is known to activate several ion currents in mammalian myocardium, little is known about the role of action potential morphology in the ISO-induced changes in ion currents. Therefore, the effects of ISO on action potential configuration, L-type Ca²âº current (I(Ca)), slow delayed rectifier K⁺ current (I(Ks)) and fast delayed rectifier K⁺ current (I(Kr)) were studied and compared in a frequency-dependent manner using canine isolated ventricular myocytes from various transmural locations. EXPERIMENTAL APPROACH: Action potentials were recorded with conventional sharp microelectrodes; ion currents were measured using conventional and action potential voltage clamp techniques. KEY RESULTS: In myocytes displaying a spike-and-dome action potential configuration (epicardial and midmyocardial cells), ISO caused reversible shortening of action potentials accompanied by elevation of the plateau. ISO-induced action potential shortening was absent in endocardial cells and in myocytes pretreated with 4-aminopyridine. Application of the I(Kr) blocker E-4031 failed to modify the ISO effect, while action potentials were lengthened by ISO in the presence of the I(Ks) blocker HMR-1556. Both action potential shortening and elevation of the plateau were prevented by pretreatment with the I(Ca) blocker nisoldipine. Action potential voltage clamp experiments revealed a prominent slowly inactivating I(Ca) followed by a rise in I(Ks) , both currents increased with increasing the cycle length. CONCLUSIONS AND IMPLICATIONS: The effect of ISO in canine ventricular cells depends critically on action potential configuration, and the ISO-induced activation of I(Ks) - but not I(Kr) - may be responsible for the observed shortening of action potentials.


Asunto(s)
Potenciales de Acción/efectos de los fármacos , Canales de Potasio de Tipo Rectificador Tardío/metabolismo , Isoproterenol/farmacología , Miocitos Cardíacos/efectos de los fármacos , Agonistas Adrenérgicos beta/farmacología , Animales , Canales de Calcio Tipo L/metabolismo , Cromanos/farmacología , Perros , Femenino , Masculino , Miocitos Cardíacos/metabolismo , Nisoldipino/farmacología , Técnicas de Placa-Clamp , Piperidinas/farmacología , Piridinas/farmacología , Sulfonamidas/farmacología
6.
Acta Physiol (Oxf) ; 206(1): 42-50, 2012 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-22520840

RESUMEN

AIM: The aim of this work was to study antagonistic interactions between the effects of various types of Ca(2+) channel blockers and isoproterenol on the amplitude of L-type Ca(2+) current in canine ventricular cells. METHODS: Whole-cell version of the patch clamp technique was used to study the effect of isoproterenol on Ca(2+) current in the absence and presence of Ca(2+) channel-blocking agents, including nifedipine, nisoldipine, diltiazem, verapamil, CoCl(2) and MnCl(2) . RESULTS: Five micromolar Nifedipine, 1 µM nisoldipine, 10 µM diltiazem, 5 µM verapamil, 3 mM CoCl(2) and 5 mM MnCl(2) evoked uniformly a 90-95% blockade of Ca(2+) current in the absence of isoproterenol. Isoproterenol (100 nM) alone increased the amplitude of Ca(2+) current from 6.8 ± 1.3 to 23.7 ± 2.2 pA/pF in a reversible manner. Isoproterenol caused a marked enhancement of Ca(2+) current even in the presence of nifedipine, nisoldipine, diltiazem and verapamil, but not in the presence of CoCl(2) or MnCl(2) . CONCLUSION: The results indicate that the action of isoproterenol is different in the presence of organic and inorganic Ca(2+) channel blockers. CoCl(2) and MnCl(2) were able to fully prevent the effect of isoproterenol on Ca(2+) current, while the organic Ca(2+) channel blockers failed to do so. This has to be born in mind when the effects of organic Ca(2+) channel blockers are evaluated either experimentally or clinically under conditions of increased sympathetic tone.


Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/metabolismo , Ventrículos Cardíacos/citología , Isoproterenol/farmacología , Miocitos Cardíacos/efectos de los fármacos , Animales , Calcio/metabolismo , Células Cultivadas , Perros , Interacciones Farmacológicas , Femenino , Masculino
7.
Curr Med Chem ; 18(24): 3737-56, 2011.
Artículo en Inglés | MEDLINE | ID: mdl-21774754

RESUMEN

Action potential voltage-clamp (APVC) is a technique to visualize the profile of various currents during the cardiac action potential. This review summarizes potential applications and limitations of APVC, the properties of the most important ion currents in nodal, atrial, and ventricular cardiomyocytes. Accordingly, the profiles ("fingerprints") of the major ion currents in canine ventricular myocytes, i.e. in cells of a species having action potential morphology and set of underlying ion currents very similar to those found in the human heart, are discussed in details. The degree of selectivity of various compounds, which is known to be a critical property of drugs used in APVC experiments, is overviewed. Thus the specificity of agents known to block sodium (tetrodotoxin, saxitoxin), potassium (chromanol 293B, HMR 1556, E-4031, dofetilide, sotalol, 4-aminopyridine, BaCl(2)), calcium (nifedipine, nisolpidine, nicardipine, diltiazem, verapamil, gallopamil), and chloride (anthracene-9-carboxylic acid, DIDS) channels, the inhibitor of the sodium-calcium exchanger (SEA0400), and the activator of sodium current (veratridine) are accordingly discussed. Based on a theory explaining how calcium current inhibitors block calcium channels, the structural comparison of the studied substances usually confirmed the results of the literature. Using these predictions, a hypothetical super-selective calcium channel inhibitor structure was designed. APVC is a valuable tool not only for studying the selectivity of the known ion channel blockers, but is also suitable for safety studies to exclude cardiac ion channel actions of any agent under development.


Asunto(s)
Potenciales de Acción , Fármacos Cardiovasculares/farmacología , Canales Iónicos/fisiología , Miocitos Cardíacos/efectos de los fármacos , Animales , Bloqueadores de los Canales de Calcio/farmacología , Perros , Humanos , Canales Iónicos/metabolismo , Técnicas de Placa-Clamp , Bloqueadores de los Canales de Potasio/farmacología , Bloqueadores de los Canales de Sodio/farmacología
8.
Curr Med Chem ; 18(24): 3714-9, 2011.
Artículo en Inglés | MEDLINE | ID: mdl-21774757

RESUMEN

Calcium ions are crucial elements of excitation-contraction coupling in cardiac myocytes. The intracellular Ca(2+ ) concentration changes continously during the cardiac cycle, but the Ca(2+ ) entering to the cell serves as an intracellular second messenger, as well. The Ca(2+ ) as a second messenger influences the activity of many intracellular signalling pathways and regulates gene expression. In cardiac myocytes the major pathway for Ca(2+ ) entry into cells is L-type calcium channel (LTCC). The precise control of LTCC function is essential for maintaining the calcium homeostasis of cardiac myocytes. Dysregulation of LTCC may result in different diseases like cardiac hypertrophy, arrhytmias, heart failure. The physiological and pathological structural changes in the heart are induced in part by small G proteins. These proteins are involved in wide spectrum of cell biological functions including protein transport, regulation of cell proliferation, migration, apoptosis, and cytoskeletal rearrangement. Understanding the crosstalk between small G proteins and LTCC may help to understand the pathomechanism of different cardiac diseases and to develop a new generation of genetically-encoded Ca(2+ ) channel inhibitors.


Asunto(s)
Canales de Calcio Tipo L/metabolismo , Calcio/metabolismo , Proteínas de Unión al GTP Monoméricas/metabolismo , Activación Enzimática/efectos de los fármacos , Cardiopatías/metabolismo , Cardiopatías/patología , Humanos , Proteínas de Unión al GTP Monoméricas/antagonistas & inhibidores , Inhibidores de Proteínas Quinasas/química , Inhibidores de Proteínas Quinasas/farmacología , Transducción de Señal
9.
Curr Med Chem ; 18(24): 3707-13, 2011.
Artículo en Inglés | MEDLINE | ID: mdl-21774758

RESUMEN

Therapeutic strategy for cardiac arrhythmias has undergone a remarkable change during the last decades. Currently implantable cardioverter defibrillator therapy is considered to be the most effective therapeutic method to treat malignant arrhythmias. Some even argue that there is no room for antiarrhythmic drug therapy in the age of implantable cardioverter defibrillators. However, in clinical practice, antiarrhythmic drug therapies are frequently needed, because implantable cardioverter defibrillators are not effective in certain types of arrhythmias (i.e. premature ventricular beats or atrial fibrillation). Furthermore, given the staggering cost of device therapy, it is economically imperative to develop alternative effective treatments. Cardiac ion channels are the target of a number of current treatment strategies, but therapies based on ion channel blockers only resulted in moderate success. Furthermore, these drugs are associated with an increased risk of proarrhythmia, systemic toxicity, and increased defibrillation threshold. In many cases, certain ion channel blockers were found to increase mortality. Other drug classes such as ßblockers, angiotensin-converting enzyme inhibitors, aldosterone antagonists, and statins appear to have proven efficacy for reducing cardiac mortality. These facts forced researchers to shift the focus of their research to molecular targets that act upstream of ion channels. One of these potential targets is calcium/calmodulin-dependent kinase II (CaMKII). Several lines of evidence converge to suggest that CaMKII inhibition may provide an effective treatment strategy for heart diseases. (1) Recent studies have elucidated that CaMKII plays a key role in modulating cardiac function and regulating hypertrophy development. (2) CaMKII activity has been found elevated in the failing hearts from human patients and animal models. (3) Inhibition of CaMKII activity has been shown to mitigate hypertrophy, prevent functional remodeling and reduce arrhythmogenic activity. In this review, we will discuss the structural and functional properties of CaMKII, the modes of its activation and the functional consequences of CaMKII activity on ion channels.


Asunto(s)
Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/antagonistas & inhibidores , Arritmias Cardíacas/tratamiento farmacológico , Arritmias Cardíacas/enzimología , Arritmias Cardíacas/patología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Canales de Cloruro/metabolismo , Diseño de Fármacos , Activación Enzimática/efectos de los fármacos , Humanos , Canales de Potasio/metabolismo , Inhibidores de Proteínas Quinasas/química , Inhibidores de Proteínas Quinasas/farmacología , Inhibidores de Proteínas Quinasas/uso terapéutico , Canales de Sodio/metabolismo
10.
Curr Med Chem ; 18(24): 3597-606, 2011.
Artículo en Inglés | MEDLINE | ID: mdl-21774765

RESUMEN

Class 3 antiarrhythmic agents exhibit reverse rate-dependent lengthening of the action potential duration (APD), i.e. changes in APD are greater at longer than at shorter cycle lengths. In spite of the several theories developed to explain this reverse rate-dependency, its mechanism has been clarified only recently. The aim of the present study is to elucidate the mechanisms responsible for reverse rate-dependency in mammalian ventricular myocardium. Action potentials were recorded using conventional sharp microelectrodes from human, canine, rabbit, guinea pig, and rat ventricular myocardium in a rate-dependent manner. Rate-dependent drug-effects of various origin were studied using agents known to lengthen or shorten action potentials allowing thus to determine the drug-induced changes in APD as a function of the cycle length. Both drug-induced lengthening and shortening of action potentials displayed reverse rate-dependency in human, canine, and guinea pig preparations, but not in rabbit and rat myocardium. Similar results were obtained when repolarization was modified by injection of inward or outward current pulses in isolated canine cardiomyocytes. In contrast to reverse rate-dependence, drug-induced changes in APD well correlated with baseline APD values (i.e. that measured before the superfusion of drug or injection of current) in all of the preparations studied. Since the net membrane current (I(net)), determined from the action potential waveform at the middle of the plateau, was inversely proportional to APD, and consequently to cycle length, it is concluded that that reverse rate-dependency may simply reflect the inverse relationship linking I(net) to APD. In summary, reverse rate-dependency is an intrinsic property of drug action in the hearts of species showing positive APD - cycle length relationship, including humans. This implies that development of a pure K(+) channel blocking agent without reverse rate-dependent effects is not likely to be successful.


Asunto(s)
Potenciales de Acción/fisiología , Antiarrítmicos/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Antiarrítmicos/química , Perros , Cobayas , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Ventrículos Cardíacos/efectos de los fármacos , Humanos , Microelectrodos , Miocitos Cardíacos/citología , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/fisiología , Bloqueadores de los Canales de Potasio/química , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio de Rectificación Interna/antagonistas & inhibidores , Canales de Potasio de Rectificación Interna/metabolismo , Conejos , Ratas , Función Ventricular/efectos de los fármacos , Función Ventricular/fisiología
11.
Br J Pharmacol ; 163(3): 499-509, 2011 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-21232044

RESUMEN

BACKGROUND AND PURPOSE: In spite of its widespread clinical application, there is little information on the cellular cardiac effects of the antidiabetic drug rosiglitazone in larger experimental animals. In the present study therefore concentration-dependent effects of rosiglitazone on action potential morphology and the underlying ion currents were studied in dog hearts. EXPERIMENTAL APPROACH: Standard microelectrode techniques, conventional whole cell patch clamp and action potential voltage clamp techniques were applied in enzymatically dispersed ventricular cells from dog hearts. KEY RESULTS: At concentrations ≥10 µM rosiglitazone decreased the amplitude of phase-1 repolarization, reduced the maximum velocity of depolarization and caused depression of the plateau potential. These effects developed rapidly and were readily reversible upon washout. Rosiglitazone suppressed several transmembrane ion currents, concentration-dependently, under conventional voltage clamp conditions and altered their kinetic properties. The EC(50) value for this inhibition was 25.2 ± 2.7 µM for the transient outward K(+) current (I(to)), 72.3 ± 9.3 µM for the rapid delayed rectifier K(+) current (I(Kr)) and 82.5 ± 9.4 µM for the L-type Ca(2+) current (I(Ca) ) with Hill coefficients close to unity. The inward rectifier K(+) current (I(K1)) was not affected by rosiglitazone up to concentrations of 100 µM. Suppression of I(to), I(Kr), and I(Ca) was confirmed also under action potential voltage clamp conditions. CONCLUSIONS AND IMPLICATIONS: Alterations in the densities and kinetic properties of ion currents may carry serious pro-arrhythmic risk in case of overdose with rosiglitazone, especially in patients having multiple cardiovascular risk factors, like elderly diabetic patients.


Asunto(s)
Potenciales de Acción/efectos de los fármacos , Hipoglucemiantes/efectos adversos , Canales Iónicos/fisiología , Células Musculares/efectos de los fármacos , Tiazolidinedionas/efectos adversos , Animales , Canales de Calcio Tipo L/fisiología , Perros , Femenino , Ventrículos Cardíacos/citología , Técnicas In Vitro , Masculino , Células Musculares/fisiología , Técnicas de Placa-Clamp , Canales de Potasio/fisiología , Rosiglitazona , Canales de Sodio/fisiología
12.
Br J Pharmacol ; 162(4): 890-6, 2011 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-20973780

RESUMEN

BACKGROUND AND PURPOSE: While the slow delayed rectifier K(+) current (I(Ks)) is known to be enhanced by the stimulation of ß-adrenoceptors in several mammalian species, phosphorylation-dependent regulation of the rapid delayed rectifier K(+) current (I(Kr)) is controversial. EXPERIMENTAL APPROACH: In the present study, therefore, the effect of isoprenaline (ISO), activators and inhibitors of the protein kinase A (PKA) pathway on I(Kr) and I(Ks) was studied in canine ventricular myocytes using the whole cell patch clamp technique. KEY RESULTS: I (Kr) was significantly increased (by 30-50%) following superfusion with ISO, forskolin or intracellular application of PKA activator cAMP analogues (cAMP, 8-Br-cAMP, 6-Bnz-cAMP). Inhibition of PKA by Rp-8-Br-cAMP had no effect on baseline I(Kr). The stimulating effect of ISO on I(Kr) was completely inhibited by selective ß1-adrenoceptor antagonists (metoprolol and CGP-20712A), by the PKA inhibitor Rp-8-Br-cAMP and by the PKA activator cAMP analogues, but not by the EPAC activator 8-pCPT-2'-O-Me-cAMP. In comparison, I(Ks) was increased threefold by the activation of PKA (by ISO or 8-Br-cAMP), and strongly reduced by the PKA inhibitor Rp-8-Br-cAMP. The ISO-induced enhancement of I(Ks) was decreased by Rp-8-Br-cAMP and completely inhibited by 8-Br-cAMP. CONCLUSIONS AND IMPLICATIONS: The results indicate that the stimulation of ß1-adrenoceptors increases I(Kr), similar to I(Ks), via the activation of PKA in canine ventricular cells.


Asunto(s)
Potenciales de Acción/efectos de los fármacos , Agonistas Adrenérgicos beta/farmacología , Canales de Potasio de Tipo Rectificador Tardío/metabolismo , Ventrículos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/efectos de los fármacos , Receptores Adrenérgicos beta 1/metabolismo , Antagonistas de Receptores Adrenérgicos beta 1/farmacología , Animales , Células Cultivadas , AMP Cíclico/análogos & derivados , Proteínas Quinasas Dependientes de AMP Cíclico/antagonistas & inhibidores , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Perros , Ventrículos Cardíacos/citología , Ventrículos Cardíacos/metabolismo , Imidazoles/farmacología , Isoproterenol/farmacología , Cinética , Metoprolol/farmacología , Miocitos Cardíacos/metabolismo , Técnicas de Placa-Clamp , Inhibidores de Proteínas Quinasas/farmacología , Transducción de Señal/efectos de los fármacos , Análisis de la Célula Individual
13.
Br J Anaesth ; 99(5): 726-33, 2007 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-17895236

RESUMEN

BACKGROUND: In spite of its widespread clinical application, there is little information on the cellular cardiac effects of articaine. In the present study, the concentration-dependent effects of articaine on action potential morphology and the underlying ion currents were studied in isolated canine ventricular cardiomyocytes. METHODS: Action potentials were recorded from the enzymatically dispersed myocytes using sharp microelectrodes (16 cells from 3 dogs). Conventional patch clamp and action potential voltage clamp arrangements were used to study the effects of articaine on transmembrane ion currents (37 cells from 14 dogs). RESULTS: Articaine-induced concentration-dependent changes in action potential configuration including shortening of the action potentials, reduction of their amplitude and maximum velocity of depolarization (V(max)), suppression of early repolarization and depression of plateau. The EC50 value obtained for the V(max) block was 162 (sd 30) microM. Both the reduction of V(max) and action potential shortening were frequency dependent: the former was more prominent at shorter, while the latter at longer pacing cycle lengths. A rate dependent V(max) block, having rapid offset kinetics [tau = 91 (20) ms], was observed in addition to tonic block. Under voltage clamp conditions, a variety of ion currents were blocked by articaine: I(Ca) [EC50 = 471 (75) microM], I(to) [EC50 = 365 (62) microM], I(K1) [EC50 = 372 (46) microM], I(Kr) [EC50 = 278 (79) microM], and I(Ks) [EC50 = 326 (65) microM]. Hill coefficients were close to unity indicating a single binding site for articaine, except for I(K1). CONCLUSIONS: Articaine can modify cardiac action potentials and ion currents at concentrations higher than the therapeutic range which can be achieved only by accidental venous injection. Since its suppressive effects on the inward and outward currents are relatively well balanced, the articaine-induced changes in action potential morphology may be moderate even in the case of overdose.


Asunto(s)
Potenciales de Acción/efectos de los fármacos , Anestésicos Locales/farmacología , Carticaína/farmacología , Miocitos Cardíacos/efectos de los fármacos , Animales , Canales de Calcio/efectos de los fármacos , Canales de Calcio/metabolismo , Células Cultivadas , Perros , Relación Dosis-Respuesta a Droga , Femenino , Ventrículos Cardíacos/efectos de los fármacos , Ventrículos Cardíacos/metabolismo , Masculino , Microelectrodos , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/fisiología , Técnicas de Placa-Clamp , Canales de Potasio/efectos de los fármacos , Canales de Potasio/metabolismo
14.
Acta Physiol (Oxf) ; 190(3): 189-98, 2007 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-17394574

RESUMEN

AIM: The aim of the present study was to give a parametric description of the most important K(+) currents flowing during canine ventricular action potential. METHODS: Inward rectifier K(+) current (I(K1)), rapid delayed rectifier K(+) current (I(Kr)), and transient outward K(+) current (I(to)) were dissected under action potential clamp conditions using BaCl(2), E-4031, and 4-aminopyridine, respectively. RESULTS: The maximum amplitude of I(to) was 3.0 +/- 0.23 pA/pF and its integral was 29.7 +/- 2.5 fC/pF. The current peaked 4.4 +/- 0.7 ms after the action potential upstroke and rapidly decayed to zero with a time constant of 7.4 +/- 0.6 ms. I(Kr) gradually increased during the plateau, peaked 7 ms before the time of maximum rate of repolarization (V(max)(-)) at -54.2 +/- 1.7 mV, had peak amplitude of 0.62 +/- 0.08 pA/pF, and integral of 57.6 +/- 6.7 fC/pF. I(K1) began to rise from -22.4 +/- 0.8 mV, peaked 1 ms after the time of V(max)(-) at -58.3 +/- 0.6 mV, had peak amplitude of 1.8 +/- 0.1 pA/pF, and integral of 61.6 +/- 6.2 fC/pF. Good correlation was observed between peak I(K1) and V(max)(-) (r = 0.93) but none between I(Kr) and V(max)(-). Neither I(K1) nor I(Kr) was frequency-dependent between 0.2 and 1.66 Hz. Congruently, I(Kr) failed to accumulate in canine myocytes at fast driving rates. CONCLUSION: Terminal repolarization is dominated by I(K1), but action potential duration is influenced by several ion currents simultaneously. As I(to) was not active during the plateau, and neither I(K1) nor I(Kr) was frequency-dependent, other currents must be responsible for the frequency dependence of action potential duration at normal and slow heart rates in canine ventricular cells.


Asunto(s)
Potenciales de Acción/fisiología , Miocitos Cardíacos/metabolismo , Canales de Potasio de Rectificación Interna/metabolismo , Potasio/metabolismo , Función Ventricular , Animales , Células Cultivadas , Perros , Electrofisiología , Femenino , Ventrículos Cardíacos/citología , Masculino , Técnicas de Placa-Clamp
15.
Acta Physiol (Oxf) ; 188(3-4): 163-71, 2006.
Artículo en Inglés | MEDLINE | ID: mdl-17054656

RESUMEN

AIM: The aim of the study was to examine the effects of testosterone and oestrogen on the ECG parameters and expression of cardiac ion channels in male and female dogs, and to compare the dofetilide-induced lengthening of QTc interval in control, castrated and hormone-treated animals. METHODS: ECG records were taken from male and female anaesthetized dogs (n = 10 in each group) before castration, after castration, and following inverted hormone substitution. The animals were challenged with dofetilide at each stage of the experiment. Finally, the hearts were excised and expression of ion channels was studied using Western blot technique. RESULTS: Heart rate was decreased and PQ interval increased by deprivation of sex hormones in both genders (orchiectomy or ovarectomy), while inverted hormonal substitution restored control values. Orchiectomy significantly increased the duration of QT and QTc intervals, QTc-dispersion and the dofetilide-induced lengthening of QTc, while testosterone treatment of castrated females had opposite effects. Intraventricular conduction (QRS duration) was independent of the endocrine status of the animals. Ovarectomy or oestrogen treatment of castrated males failed to alter significantly these parameters except for QTc-dispersion. Expression of ion channel proteins responsible for mediation of I(K1) and I(to) currents (Kir2.1 and Kv4.3, respectively), was significantly higher in the testosterone-treated castrated females and normal males than in the oestrogen-treated castrated males and normal females. CONCLUSION: Repolarization of canine ventricular myocardium is significantly modified by testosterone, but not oestrogen, in both genders. This effect is likely due to augmentation of expression of K(+)-channel proteins, and thus may provide protection against arrhythmias via increasing the repolarization reserve.


Asunto(s)
Andrógenos/farmacología , Estradiol/análogos & derivados , Estrógenos/farmacología , Corazón/efectos de los fármacos , Canales Iónicos/efectos de los fármacos , Testosterona/análogos & derivados , Animales , Antiarrítmicos/farmacología , Nodo Atrioventricular/efectos de los fármacos , Castración , Perros , Electrocardiografía/métodos , Estradiol/sangre , Estradiol/farmacología , Femenino , Corazón/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Canales Iónicos/análisis , Canales Iónicos/metabolismo , Masculino , Modelos Animales , Fenetilaminas/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Sulfonamidas/farmacología , Testosterona/sangre , Testosterona/farmacología , Función Ventricular/efectos de los fármacos , Función Ventricular/fisiología
16.
Acta Physiol Scand ; 180(1): 39-47, 2004 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-14706111

RESUMEN

AIMS: Present study was performed to compare the dynamics of human L-type calcium current (ICa,L) flowing during rectangular voltage pulses, voltage ramps, and action potentials (APs) recorded from epicardiac and endocardiac canine ventricular cells. METHODS: ICa,L was recorded in single myocytes isolated from undiseased human hearts using the whole cell voltage clamp technique. RESULTS: The decay of ICa,L was monotonic when using rectangular pulses or endocardial APs as voltage commands, whereas the current became double-peaked (displaying a second rise and fall) during epicardial (EPI) APs or voltage ramps used to mimic EPI APs. These ICa,L profiles were associated with single-hooked and double-hooked phase-plane trajectories, respectively. No sustained current was observed during the AP commands. Kinetics of deactivation and recovery from inactivation of human ICa,L were determined using twin-pulse voltage protocols and voltage ramps, and the results were similar to those obtained previously in canine cells under identical experimental conditions. CONCLUSIONS: ICa,L can inactivate partially before and deactivate during the phase-1 repolarization of the epicardiac AP, and reopening of these channels seems to be associated with formation of the dome.


Asunto(s)
Potenciales de Acción/fisiología , Canales de Calcio Tipo L/fisiología , Células Musculares/fisiología , Función Ventricular , Técnicas de Cultivo de Célula , Ventrículos Cardíacos/citología , Humanos , Cinética , Técnicas de Placa-Clamp/métodos , Factores de Tiempo
17.
Acta Physiol Scand ; 178(1): 11-8, 2003 May.
Artículo en Inglés | MEDLINE | ID: mdl-12713510

RESUMEN

AIM: The aim of this study was to compare the action potential configuration, contractility, intracellular Ca2+ and H+ concentrations in mammalian cardiac tissues bathed with Krebs and Tyrode solutions at 37 degrees C. RESULTS: In Langendorff-perfused guinea-pig hearts, loaded with the fluorescent Ca2+-indicator Fura-2, or H+-sensitive dye carboxy-SNARF, shifts from Krebs to Tyrode solution caused intra-cellular acidification, increased diastolic pressure and [Ca2+]i, decreased systolic pressure and [Ca2+]i, leading to a reduction in the amplitude of [Ca2+]i transients and pulse pressure. Contractility was also depressed in canine ventricular trabeculae when transferred from Krebs to Tyrode solution. Shifts from Krebs to Tyrode solution increased the duration of action potentials in multicellular cardiac preparations excised from canine and rabbit hearts but not in isolated cardiomyocytes. All these changes in action potential morphology, contractility, [Ca2+]i and [H+]i were readily reversible by addition of 26 mmol L(-1) bicarbonate to Tyrode solution. Effects of dofetilide and CsCl, both blockers of the delayed rectifier K current, on action potential duration were compared in Krebs and Tyrode solutions. Dofetilide lengthened rabbit ventricular action potentials in a significantly greater extent in Tyrode than in Krebs solution. Exposure of canine Purkinje fibres to CsCl evoked early after depolarizations within 40 min in all preparations incubated with Tyrode solution, but not in those bathed with Krebs solution. CONCLUSION: It is concluded that the marked differences in action potential morphology, [Ca2+]i, [H+]i and contractility observed between preparations bathed with Krebs and Tyrode solutions are more likely attributable to differences in the intracellular buffering capacities of the two media.


Asunto(s)
Potenciales de Acción/fisiología , Calcio/análisis , Corazón/fisiología , Contracción Miocárdica/fisiología , Protones , Potenciales de Acción/efectos de los fármacos , Animales , Bicarbonatos/farmacología , Presión Sanguínea/efectos de los fármacos , Cesio/farmacología , Cloruros/farmacología , Perros , Cobayas , HEPES/farmacología , Corazón/efectos de los fármacos , Ventrículos Cardíacos/efectos de los fármacos , Masculino , Contracción Miocárdica/efectos de los fármacos , Músculos Papilares/efectos de los fármacos , Músculos Papilares/fisiología , Fenetilaminas/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Ramos Subendocárdicos/efectos de los fármacos , Ramos Subendocárdicos/fisiología , Conejos , Sulfonamidas/farmacología , Función Ventricular
18.
Gen Physiol Biophys ; 22(3): 341-53, 2003 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-14986885

RESUMEN

The physiological role of chloride currents (Icl) in cardiac cells is poorly understood. The aim of the present study was to reveal the role of Icl in the genesis of early and delayed afterdepolarisations (EADs and DADs, respectively). First we identified Icl under action potential voltage clamp conditions as the anthracene-9-carboxylic acid (ANTRA) (0.5 mmol/l)-sensitive current. The ANTRA-sensitive current was large and outwardly directed at the beginning, while it was moderate and inwardly directed at the end of the action potential. Application of ANTRA under current clamp conditions decreased the depth of the incisura, shifted the plateau upwards and lengthened the duration of action potentials. The effect of ANTRA was studied in three models of afterdepolarisations: the ouabain-induced DAD model, the caesium-induced EAD model, and in the presence of subthreshold concentration of isoproterenol. Preincubation of the cells with 0.5 mmol/l ANTRA failed to induce afterdepolarisations. Ouabain (200 nmol/l) alone caused DADs in 62.5% of the cells within 15 min. When ouabain was applied in the presence of ANTRA, 60% of the myocytes transiently displayed EADs before the development of DADs, and all cells developed DADs within 7 min. Isoproterenol (5 nmol/l) alone failed to induce afterdepolarisations. However, 75% of the cells produced DADs within 6 min when superfused with isoproterenol in the presence of ANTRA. Incubation of the myocytes with 3.6 mmol/l CsCl caused EADs in 71.4% of the cells within 30 min. Application of CsCl in the presence of ANTRA resulted in immediate depolarisation of the membrane from -79.6 +/- 0.4 to -54.2 +/- 3.5 mV. Summarizing our results we conclude that the ANTRA-sensitive current is an important mechanism of defence against afterdepolarisations. Suppression of Icl may thus increase the incidence and accelerate the rate of development of both EADs and DADs.


Asunto(s)
Potenciales de Acción/fisiología , Antracenos/farmacología , Membrana Celular/fisiología , Canales de Cloruro/fisiología , Cloro/metabolismo , Sistema de Conducción Cardíaco/fisiología , Miocitos Cardíacos/fisiología , Potenciales de Acción/efectos de los fármacos , Animales , Membrana Celular/efectos de los fármacos , Células Cultivadas , Canales de Cloruro/efectos de los fármacos , Perros , Femenino , Sistema de Conducción Cardíaco/efectos de los fármacos , Activación del Canal Iónico/efectos de los fármacos , Activación del Canal Iónico/fisiología , Isoproterenol/farmacología , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Miocitos Cardíacos/efectos de los fármacos , Ouabaína/farmacología
19.
Naunyn Schmiedebergs Arch Pharmacol ; 363(6): 604-11, 2001 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-11414655

RESUMEN

Based on earlier pharmacological studies performed using conventional microelectrodes EGIS-7229 (S 21407), the novel antiarrhythmic candidate, was suggested to have a combined mode of action in cardiac tissues isolated from various mammalian species. In order to characterize the electrophysiological effects of the compound, its effects on calcium and potassium currents of isolated canine ventricular cardiomyocytes were studied in the present work using the whole cell configuration of the patch clamp technique. L-type Ca current (ICa) was significantly depressed by EGIS-7229 at concentrations of 3 microM or higher with no concomitant changes in the voltage-dependence of activation and time course of inactivation of ICa. The drug reversibly suppressed the rapid component of the delayed rectifier K current (IKr) in a concentration-dependent manner, having a K0.5 value of 1.1+/-0.1 microM and a slope factor of close to unity (1.23+/-0.16), indicating that probably one single binding site of high affinity may be involved in binding of EGIS-7229 to the IKr channel. In contrast, no changes in the slow component of the delayed rectifier K current (IKs) was observed with the compound up to the concentration of 100 microM, even if the current was fully activated by 8-bromo-cAMP. At a concentration of 10 microM or higher, EGIS-7229 caused also a moderate but significant reduction in the inward rectifier K current (IK1) and the transient outward K current (Ito) with no change in the voltage-dependence of activation and steady-state inactivation of Ito. Present results indicate that EGIS-7229 can be considered as a selective IKr blocker at low (1 microM) concentration; however, its combined (class III + IV) mechanism of action is evident at concentrations of 3 microM or higher. Suppression of ICa may explain the lack of development of early afterdepolarizations in the presence of EGIS-7229, predicting a relatively safe clinical application in contrast to pure class III compounds.


Asunto(s)
Antiarrítmicos/farmacología , Canales de Calcio/efectos de los fármacos , Corazón/efectos de los fármacos , Canales de Potasio/efectos de los fármacos , Piridazinas/farmacología , Análisis de Varianza , Animales , Perros , Electrofisiología , Corazón/fisiología , Humanos , Técnicas de Placa-Clamp
20.
Naunyn Schmiedebergs Arch Pharmacol ; 363(4): 383-90, 2001 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-11330331

RESUMEN

Effects of endothelin-1 (ET-1) on the L-type calcium current (ICa) and delayed rectifier potassium current (IK) were studied in isolated canine ventricular cardiomyocytes using the whole-cell configuration of the patch-clamp technique. ET-1 (8 nM) was applied in three experimental arrangements: untreated cells, in the presence of 50 nM isoproterenol, and in the presence of 250 microM 8-bromo-cAMP. In untreated cells, ET-1 significantly decreased the peak amplitude of ICa by 32.3+/-4.8% at +5 mV (P<0.05) without changing activation or inactivation characteristics of ICa. ET-1 had no effect on the amplitude of IK, Ito (transient outward current) or IK1 (inward rectifier K current) in untreated cells; however, the time course of recovery from inactivation of Ito was significantly increased by ET-1 (from 26.5+/-4.6 ms to 59.5+/- 1.8 ms, P < 0.05). Amplitude and time course of intracellular calcium transients, recorded in voltage-clamped cells previously loaded with the fluorescent calcium indicator dye Fura-2, were not affected by ET-1. ET-1 had no effect on force of contraction in canine ventricular trabeculae. Isoproterenol increased the amplitude of ICa to 263+/-29% of control. ET-1 reduced ICa also in isoproterenol-treated cells by 17.8+/-2% (P<0.05); this inhibition was significantly less than obtained in untreated cells. IK was increased by isoproterenol to 213+/-18% of control. This effect of isoproterenol on IK was reduced by 31.8+/-4.8% if the cells were pretreated with ET-1. Similarly, in isoproterenol-treated cells ET-1 decreased IK by 16.2+/-1.5% (P<0.05). Maximal activation of protein kinase A (PKA) was achieved by application of 8-bromo-cAMP in the pipette solution. In the presence of 8-bromo-cAMP ET-1 failed to alter ICa or IK It was concluded that differences in effects of ET-1 on ICa and IK may be related to differences in cAMP sensitivity of the currents.


Asunto(s)
Canales de Calcio/efectos de los fármacos , Endotelina-1/farmacología , Canales de Potasio/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Análisis de Varianza , Animales , Cardiotónicos/farmacología , AMP Cíclico/metabolismo , Perros , Ventrículos Cardíacos/efectos de los fármacos , Isoproterenol/farmacología , Contracción Miocárdica/efectos de los fármacos , Técnicas de Placa-Clamp
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