RESUMEN
The effects of K(+)-channel blockers on the action potential duration of the myocardium were examined in isolated right ventricles from the 7 - 10-day-old, 11 - 13-day-old, and 14 - 20-day-old embryo and 1 - 7-day-old hatched chicks. E-4031 significantly prolonged action potential duration at all developmental stages examined; the prolongation was largest in the 11 - 13-day-old embryo and was accompanied by early after-depolarizations. Chromanol 293B showed smaller prolongation at all stages examined. Terfenadine prolonged action potential duration in the 11 - 13-day-old embryo, but not in other stages. Thus, the chick ventricular myocardium changes its repolarization properties during development.
Asunto(s)
Potenciales de Acción/efectos de los fármacos , Canales de Potasio de Tipo Rectificador Tardío/antagonistas & inhibidores , Ventrículos Cardíacos/efectos de los fármacos , Miocardio/metabolismo , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio/metabolismo , Animales , Arritmias Cardíacas/inducido químicamente , Arritmias Cardíacas/fisiopatología , Embrión de Pollo , Canales de Potasio de Tipo Rectificador Tardío/metabolismo , Evaluación Preclínica de Medicamentos , Síndrome de QT Prolongado/inducido químicamente , Síndrome de QT Prolongado/fisiopatologíaRESUMEN
The effects of K+-channel blockers on the action potential duration of the myocardium were examined in isolated right ventricles from the 7 - 10-day-old, 11 - 13-day-old, and 14 - 20-day-old embryo and 1 - 7-day-old hatched chicks. E-4031 significantly prolonged action potential duration at all developmental stages examined; the prolongation was largest in the 11 - 13-day-old embryo and was accompanied by early after-depolarizations. Chromanol 293B showed smaller prolongation at all stages examined. Terfenadine prolonged action potential duration in the 11 - 13-day-old embryo, but not in other stages. Thus, the chick ventricular myocardium changes its repolarization properties during development.
RESUMEN
We examined the involvement of the Na(+)/Ca(2+) exchanger in the automaticity of the pulmonary vein myocardium with a specific inhibitor, SEA0400. Action potentials were recorded from the myocardial layer of isolated guinea-pig pulmonary vein preparations, and Ca(2+) transients were recorded from the cardiomyocytes. Spontaneous electrical activity was observed in 17.7% of the preparations, which was inhibited by either SEA0400 or ryanodine. In quiescent preparations, ouabain induced electrical activity and spontaneous Ca(2+) transients, which were inhibited by SEA0400, as well as ryanodine. These results provide pharmacological evidence that the Na(+)/Ca(2+) exchanger underlies the automaticity of the pulmonary vein myocardium.
Asunto(s)
Compuestos de Anilina , Corazón/fisiología , Éteres Fenílicos , Venas Pulmonares/fisiología , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Intercambiador de Sodio-Calcio/fisiología , Potenciales de Acción/efectos de los fármacos , Animales , Cardiotónicos/farmacología , Femenino , Cobayas , Corazón/efectos de los fármacos , Técnicas In Vitro , Masculino , Microscopía Confocal , Ouabaína/farmacología , Venas Pulmonares/efectos de los fármacos , Rianodina/farmacologíaRESUMEN
The waveform of the myocardial action potential (AP) triggering contraction differs among the species, developmental stage, and pathological state. The species difference in heart rate, which inversely correlates with body size, originates in the ion-channel mechanisms responsible for diastolic depolarization of the sinoatrial node. In some cases, such as the chronically AV-blocked dog and 11- to 13-day chick embryo, the repolarization reserve is decreased making the heart useful for drug evaluation. The degree of dependence of contraction on sarcoplasmic reticulum (SR) function increases during development. The large SR dependence and short AP of the adult mouse and rat support their rapid contraction under high heart rate. The function of the Na(+)/Ca(2+) exchanger is affected by AP waveform and ion concentrations; its major role is Ca(2+) extrusion, but under pathological conditions such as ischemia-reperfusion, it allows Ca(2+) influx and leads to myocardial injury, including loss of mitochondrial function. The role of mitochondria in ATP supply is less in the fetus where glycolysis plays a greater role. The pharmacological properties of the myocardium are affected by all of these factors and also by autonomic innervation and the hormonal status. Such comprehensive understanding is indispensable for the development of novel therapeutic strategies.
Asunto(s)
Calcio/metabolismo , Cardiopatías/tratamiento farmacológico , Contracción Miocárdica/fisiología , Potenciales de Acción , Adenosina Trifosfato/metabolismo , Animales , Modelos Animales de Enfermedad , Humanos , Canales Iónicos/metabolismo , Mitocondrias Cardíacas/metabolismo , Especificidad de la EspecieRESUMEN
Electrophysiological properties of the pulmonary vein myocardium were assessed in a canine chronic atrioventricular block model resulting in left atrial volume overload. Five chronic atrioventricular block dogs and five sham-operated dogs were used. The heart was removed two months after a surgical procedure causing atrioventricular block, when atrial structural remodeling was established. Standard microelectrode penetrations were made with glass microelectrodes to obtain action potential signals of left atrium and pulmonary vein myocardia. The resting membrane potential in the pulmonary vein was more positive than that in the left atrium (-69 mV vs -74 mV) in both animal groups. The action potential duration at 50% repolarization of the pulmonary vein was shorter in the chronic atrioventricular block dogs than in the sham-operated dogs (38 ms vs 63 ms), whereas no significant difference was detected in the action potential duration of the left atrium between the two animal groups (67 ms vs 61 ms). The action potential duration of the pulmonary vein in the chronic atrioventricular block dogs was prolonged by charybdotoxin but not by iberiotoxin. Such prolongation was not observed in the normal pulmonary vein. These results suggest that long-term left atrial dilatation shortened the action potential duration of pulmonary vein myocardium, which may be associated with activation of the intermediate conductance Ca2+-activated K+ channel (IK channel).
Asunto(s)
Función del Atrio Izquierdo , Bloqueo Atrioventricular/fisiopatología , Canales de Potasio de Conductancia Intermedia Activados por el Calcio/metabolismo , Miocardio/metabolismo , Venas Pulmonares/fisiopatología , Potenciales de Acción , Animales , Función del Atrio Izquierdo/efectos de los fármacos , Bloqueo Atrioventricular/metabolismo , Bloqueo Atrioventricular/patología , Caribdotoxina/farmacología , Enfermedad Crónica , Dilatación Patológica , Modelos Animales de Enfermedad , Perros , Atrios Cardíacos/metabolismo , Atrios Cardíacos/patología , Atrios Cardíacos/fisiopatología , Canales de Potasio de Conductancia Intermedia Activados por el Calcio/antagonistas & inhibidores , Péptidos/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Venas Pulmonares/efectos de los fármacos , Venas Pulmonares/metabolismo , Factores de TiempoRESUMEN
The contribution of the T-type Ca2+ current to cardiac pacemaking was examined in isolated right atrial tissue from the mouse, guinea pig, and rabbit using a specific blocker, R(-)-efonidipine. At 10(-6) M, R(-)-efonidipine produced negative chronotropy, which was prominent in the mouse and small but significant in the guinea pig. No effect was observed in the rabbit. Microelectrode recordings revealed that R(-)-efonidipine significantly prolongs the pacemaker (phase 4) depolarization of the sinoatrial-node action potential in the mouse and guinea pig. These results provide the first pharmacological evidence that the contribution of T-type Ca2+ current to cardiac pacemaking differs among experimental animal species.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo T/efectos de los fármacos , Dihidropiridinas/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Nitrofenoles/farmacología , Nodo Sinoatrial/efectos de los fármacos , Potenciales de Acción , Animales , Canales de Calcio Tipo T/metabolismo , Cobayas , Atrios Cardíacos/efectos de los fármacos , Atrios Cardíacos/metabolismo , Técnicas In Vitro , Ratones , Microelectrodos , Compuestos Organofosforados/farmacología , Conejos , Nodo Sinoatrial/metabolismo , Especificidad de la Especie , Factores de TiempoRESUMEN
We examined the intracellular mechanisms for endothelin-1-induced positive and negative inotropic components that coexist in the mouse ventricular myocardium using isolated ventricular tissue and myocytes from 4-week-old mice. In the presence of SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, endothelin-1 produced positive inotropy. Endothelin-1, when applied to cardiomyocytes in the presence of SEA0400, did not change the peak amplitude of the Ca2+ transient but increased intracellular pH and Ca2+ sensitivity of contractile proteins. On the other hand, in the presence of dimethylamiloride (DMA), a specific inhibitor of the Na+-H+ exchanger, endothelin-1 produced negative inotropy. In cardiomyocytes, in the presence of DMA, endothelin-1 produced a decrease in peak amplitude of the Ca2+ transient. In the presence of both DMA and SEA0400, endothelin-1 produced neither positive nor negative inotropy. Positive inotropy was blocked by BQ-123 and negative inotropy by BQ-788. These results suggested that endothelin-1-induced positive inotropy is mediated by ET(A) receptors, activation of the Na+-H+ exchanger and an increase in intracellular pH and Ca2+ sensitivity and that the negative inotropy is mediated by ET(B) receptors, activation of the Na+-Ca2+ exchanger and decrease in Ca2+ transient amplitude.
Asunto(s)
Endotelina-1/fisiología , Miocitos Cardíacos/fisiología , Receptor de Endotelina A/fisiología , Receptor de Endotelina B/fisiología , Intercambiador de Sodio-Calcio/fisiología , Intercambiadores de Sodio-Hidrógeno/fisiología , Amilorida/análogos & derivados , Amilorida/farmacología , Análisis de Varianza , Compuestos de Anilina/farmacología , Animales , Calcio/fisiología , Cardiotónicos/farmacología , Relación Dosis-Respuesta a Droga , Endotelina-1/farmacología , Ventrículos Cardíacos/citología , Concentración de Iones de Hidrógeno , Técnicas In Vitro , Ratones , Ratones Endogámicos , Contracción Miocárdica/efectos de los fármacos , Miocitos Cardíacos/efectos de los fármacos , Oligopéptidos/farmacología , Péptidos Cíclicos/farmacología , Éteres Fenílicos/farmacología , Piperidinas/farmacología , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Intercambiadores de Sodio-Hidrógeno/antagonistas & inhibidoresRESUMEN
The organ selectivity and the effect on myocardial ischemia-reperfusion injury of (R)-acetoxyhexamide ((R)-ACX), a novel sulfonylurea, were examined. (R)-ACX, as well as glibenclamide, concentration-dependently stimulated insulin release from INS-1 cell, a cell line derived from pancreatic beta-cells. The potency of (R)-ACX was about 1/10 of that of glibenclamide. In isolated guinea pig ventricular myocardial tissue, glibenclamide concentration-dependently inhibited the action potential shortening by NIP-121, an ATP-sensitive potassium channel opener, but (R)-ACX showed only slight inhibition. In isolated rat aortic rings contracted with norepinephrine, glibenclamide concentration-dependently inhibited the relaxation by NIP-121, while (R)-ACX showed only slight inhibition. In coronary-perfused guinea pig ventricular preparations, glibenclamide reduced the recovery of contractile force after ischemia-reperfusion, while (R)-ACX did not. In conclusion, (R)-ACX is a beta-cell selective sulfonylurea which, unlike glibenclamide, does not aggravate cardiac ischemia-reperfusion damage.
Asunto(s)
Células Secretoras de Insulina/efectos de los fármacos , Daño por Reperfusión Miocárdica/fisiopatología , Compuestos de Sulfonilurea/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Benzopiranos/farmacología , Células Cultivadas , Femenino , Gliburida/farmacología , Gliburida/toxicidad , Cobayas , Hipoglucemiantes/farmacología , Hipoglucemiantes/toxicidad , Técnicas In Vitro , Masculino , Relajación Muscular/efectos de los fármacos , Músculo Liso Vascular/efectos de los fármacos , Contracción Miocárdica/efectos de los fármacos , Músculos Papilares/efectos de los fármacos , RatasRESUMEN
We examined the source of Ca(2+) involved in the volume regulation of Madin-Darby canine kidney (MDCK) cells with confocal microscopy and fluoroprobes. Hyposmosis induced a transient increase in cell volume, as well as cytoplasmic Ca(2+), which peaked at 3 to 5 min and gradually decreased to reach the initial value within about 30 min. This late decrease in cell volume, as well as the transient rise in cytoplasmic Ca(2+), was reduced in Ca(2+)-free solution and was abolished by pretreatment with thapsigargin. In conclusion, Ca(2+) released from the intracellular store contributes to the regulatory volume decrease following hyposmotic swelling in MDCK cells.
Asunto(s)
Calcio/metabolismo , Tamaño de la Célula , Riñón/citología , Animales , Línea Celular , Perros , Microscopía Confocal , Microscopía Fluorescente , Concentración Osmolar , Tapsigargina , Factores de TiempoRESUMEN
Positive inotropy by sarcoplasmic/endoplasmic reticulum Ca(2+) pump inhibitors was found and its mechanisms were analyzed pharmacologically. Thapsigargin and cyclopiazonic acid produced positive inotropy in isolated mouse left atria. The responses were inhibited by pretreatment of the endocardial surface with Triton X-100 or by indomethacin, which suggests that the inotropic responses were mediated by prostaglandin(s) released from the endocardial endothelium as well as acetylcholine-induced positive inotropy. The thapsigargin- and acetylcholine-induced positive inotropy was significantly inhibited by Gd(3+), La(3+) and lavendustin A, a tyrosine kinase inhibitor, but not by Ni(2+) and LOE908, a non-selective cation channel inhibitor. Gd(3+) and lavendustin A had no effect on the exogenously applied PGF(2)alpha-induced positive inotropy. In addition, acetylcholine did not induce any positive inotropy when applied after the application of thapsigargin. These results strongly suggest that thapsigargin- as well as acetylcholine-induced prostaglandin release from endocardial endothelium is mediated by store-operated Ca(2+) entry through Gd(3+)-sensitive channels and activation of tyrosine kinase.
Asunto(s)
ATPasas Transportadoras de Calcio/antagonistas & inhibidores , Calcio/metabolismo , Endotelio Vascular/fisiología , Indoles/farmacología , Contracción Miocárdica/efectos de los fármacos , Tapsigargina/farmacología , Acetilcolina/farmacología , Animales , Canales de Calcio/fisiología , Dinoprost/farmacología , Gadolinio/farmacología , Ratones , Estimulación QuímicaRESUMEN
Involvement of the Na+/Ca2+ exchanger in ouabain-induced inotropy and arrhythmogenesis was examined with a specific inhibitor, SEA0400. In right ventricular papillary muscle isolated from guinea-pig ventricle, 1 microM SEA0400, which specifically inhibits the Na+/Ca2+ exchanger by 80%, reduced the ouabain (1 microM)-induced positive inotropy by 40%, but had no effect on the inotropy induced by 100 microM isobutyl methylxantine. SEA0400 significantly inhibited the contracture induced by low Na+ solution. In HEK293 cells expressing the Na+/Ca2+ exchanger, 1 microM ouabain induced an increase in intracellular Ca2+, which was inhibited by SEA0400. The arrhythmic contractions induced by 3 microM ouabain were significantly reduced by SEA0400. These results provide pharmacological evidence that the Na+/Ca2+ exchanger is involved in ouabain-induced inotropy and arrhythmogenesis.
Asunto(s)
Compuestos de Anilina/farmacología , Antiarrítmicos/farmacología , Arritmias Cardíacas/fisiopatología , Cardiotónicos/farmacología , Inhibidores Enzimáticos/farmacología , Ouabaína/farmacología , Éteres Fenílicos/farmacología , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Intercambiador de Sodio-Calcio/fisiología , 1-Metil-3-Isobutilxantina/farmacología , Animales , Arritmias Cardíacas/inducido químicamente , Calcio/metabolismo , Línea Celular , Citoplasma/efectos de los fármacos , Citoplasma/metabolismo , Cobayas , Técnicas In Vitro , Contracción Miocárdica/efectos de los fármacos , Músculos Papilares , Inhibidores de Fosfodiesterasa/farmacologíaRESUMEN
The chronic atrioventricular block dog is a useful model for predicting the future onset of drug-induced long QT syndrome in clinical practice. To better understand the arrhythmogenic profile of this model, we recorded the action potentials of the isolated ventricular tissues in the presence and absence of the class III antiarrhythmic drug nifekalant. The action potential durations of the Purkinje fiber and free wall of the right ventricle were longer in the chronic atrioventricular block dogs than in the dogs with normal sinus rhythm. Nifekalant in concentrations of 1 and 10 microM prolonged the action potential durations of Purkinje fiber and the free wall in a concentration-dependent manner. The extent of prolongation was greater in the chronic atrioventricular block dogs than in the normal dogs. However, increase of temporal dispersion of ventricular repolarization including early afterdepolarization was not detected by nifekalant in either group of dogs, indicating lack of potential to trigger arrhythmias in vitro. These results suggest that the ventricular repolarization delay in the chronic atrioventricular block model by nifekalant may largely depend on the decreased myocardial repolarization reserve, whereas the trigger for lethal arrhythmia was not generated in the in vitro condition in contrast to the in vivo experiment.
Asunto(s)
Antiarrítmicos/farmacología , Arritmias Cardíacas/fisiopatología , Bloqueo Cardíaco/fisiopatología , Pirimidinonas/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Perros , Relación Dosis-Respuesta a Droga , Ventrículos Cardíacos/efectos de los fármacos , Microelectrodos , Ramos Subendocárdicos/efectos de los fármacosRESUMEN
The inotropic response to muscarinic receptor stimulation of isolated chick ventricular myocardium was examined at various developmental stages, and the receptor subtype involved was pharmacologically characterized. In embryonic chick ventricles, carbachol (CCh) produced positive inotropy at micromolar concentrations. In hatched chick ventricles, CCh produced negative inotropy at nanomolar concentrations. Neither positive nor negative inotropy was observed in the 19 - 21-day-old embryos. Both positive and negative inotropy were also observed with acetylcholine and oxotremoline-M. The CCh-induced positive inotropy in 7 - 9-day-old embryonic ventricles and the negative inotropy in 1 - 3-day-old hatched chick ventricles were antagonized by muscarinic receptor antagonists; pA(2) values for the positive and negative responses of pirenzepine were 7.5 and 7.2, those of AF-DX116 (11-[(2-[(diethylamino)methyl]-1-piperidinyl)acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4] benzodiazepine-6-one) were 6.8 and 6.9, those of 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) were 9.0 and 8.5, and those of himbacine were 7.0 and 8.0, respectively. CCh had no effect on action potential configuration. In conclusion, the positive inotropy is most likely mediated by muscarinic M(1) receptors and the negative inotropy is mostly likely mediated by muscarinic M(4) receptors.
Asunto(s)
Contracción Miocárdica/efectos de los fármacos , Receptores Muscarínicos/fisiología , Potenciales de Acción/efectos de los fármacos , Alcaloides/farmacología , Animales , Carbacol/farmacología , Embrión de Pollo , Relación Dosis-Respuesta a Droga , Furanos/farmacología , Ventrículos Cardíacos , Naftalenos/farmacología , Piperidinas/farmacología , Pirenzepina/análogos & derivados , Pirenzepina/farmacología , Receptores Muscarínicos/clasificaciónRESUMEN
We developed a method to quantitatively evaluate the potency of Na+/Ca2+ exchanger (NCX) inhibitors with fluorescence microscopy in NCX1-transfected HEK 293 cells. The reverse mode and forward mode NCX activities were measured as the ascending slope of the early phase increase in cytoplasmic Ca2+ concentration after change to low Na+ extracellular solution and the descending rate (inverse of the exponential time constant) on return to normal solution, respectively. Both modes of NCX were inhibited by SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline) and KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate), and the concentration-inhibition relationships for both inhibitors were in good agreement with those previously reported in voltage clamped cardiomyocytes.
Asunto(s)
Fluorescencia , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Intercambiador de Sodio-Calcio/metabolismo , Compuestos de Anilina/farmacología , Animales , Calcio/metabolismo , Bovinos , Línea Celular , Proteínas Fluorescentes Verdes/química , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Humanos , Transporte Iónico/efectos de los fármacos , Cinética , Éteres Fenílicos/farmacología , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Sodio/farmacología , Intercambiador de Sodio-Calcio/genética , Tiourea/análogos & derivados , Tiourea/farmacología , Transfección/métodosRESUMEN
Mechanisms for the atria-specific action potential-prolonging action of NIP-142 ((3R*,4S*)-4-cyclopropylamino-3,4-dihydro-2,2-dimethyl-6-(4-methoxyphenylacetylamino)-7-nitro-2H-1-benzopyran-3-ol), a benzopyran compound that terminates experimental atrial arrhythmia, was examined. In isolated guinea-pig atrial tissue, NIP-142 reversed the shortening of action potential duration induced by either carbachol or adenosine. These effects were mimicked by tertiapin, but not by E-4031. NIP-142 concentration-dependently blocked the human G protein-coupled inwardly rectifying potassium channel current (GIRK1/4 channel current) expressed in HEK-293 cells with an EC50 value of 0.64 microM. At higher concentrations, NIP-142 blocked the human ether a go-go related gene (HERG) channel current with an EC50 value of 44 microM. In isolated guinea-pig papillary muscles, NIP-142 had no effect on the negative inotropic effect of carbachol under beta-adrenergic stimulation, indicating lack of effect on the muscarinic receptor and Gi protein. These results suggest that NIP-142 directly inhibits the acetylcholine-activated potassium current.
Asunto(s)
Antiarrítmicos/farmacología , Función Atrial/efectos de los fármacos , Benzopiranos/farmacología , Carbacol/farmacología , Canales de Potasio Rectificados Internamente Asociados a la Proteína G/antagonistas & inhibidores , Potenciales de Acción/efectos de los fármacos , Adenosina/farmacología , Animales , Función Atrial/fisiología , Atropina/farmacología , Venenos de Abeja/farmacología , Carbacol/antagonistas & inhibidores , Línea Celular , Colforsina/farmacología , Relación Dosis-Respuesta a Droga , Canales de Potasio Éter-A-Go-Go/antagonistas & inhibidores , Canales de Potasio Éter-A-Go-Go/fisiología , Canales de Potasio Rectificados Internamente Asociados a la Proteína G/fisiología , Cobayas , Humanos , Técnicas In Vitro , Contracción Miocárdica/efectos de los fármacos , Músculos Papilares/efectos de los fármacos , Músculos Papilares/fisiología , Técnicas de Placa-Clamp , Bloqueadores de los Canales de Potasio/farmacología , Factores de TiempoRESUMEN
The cardioprotective effects of SEA0400, a novel Na(+)-Ca(2+) exchanger inhibitor, were examined in isolated guinea pig myocardial tissue and ventricular myocytes. In a coronary-perfused right ventricular tissue preparation, SEA0400 had no cardiosuppressive effect during normoxia and experimental ischemia, but enhanced the recovery of contractile force during reperfusion. SEA0400 had no effect on tissue ATP content during normoxia, but attenuated its decrease during ischemia. Treatment of ventricular myocytes with an ischemia mimetic solution (high K(+), glucose free, pH 6.0, gassed with N(2)) resulted in the depolarization of the mitochondrial membrane potential and an increase in cytoplasmic and mitochondrial Ca(2+) concentration, which had a similar time course. SEA0400 significantly delayed these changes. These results suggest that SEA0400 maintains mitochondrial function and tissue ATP content during ischemia through the inhibition of cytoplasmic and mitochondrial Ca(2+) overload.
Asunto(s)
Compuestos de Anilina/farmacología , Calcio/metabolismo , Citoplasma/efectos de los fármacos , Mitocondrias Cardíacas/efectos de los fármacos , Isquemia Miocárdica/metabolismo , Daño por Reperfusión Miocárdica/prevención & control , Éteres Fenílicos/farmacología , Intercambiador de Sodio-Calcio/antagonistas & inhibidores , Adenosina Trifosfato/metabolismo , Animales , Citoplasma/metabolismo , Cobayas , Ventrículos Cardíacos/efectos de los fármacos , Ventrículos Cardíacos/metabolismo , Técnicas In Vitro , Potencial de la Membrana Mitocondrial/efectos de los fármacos , Mitocondrias Cardíacas/metabolismo , Contracción Miocárdica/efectos de los fármacos , Isquemia Miocárdica/fisiopatología , Daño por Reperfusión Miocárdica/metabolismo , Daño por Reperfusión Miocárdica/fisiopatología , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/metabolismo , Intercambiador de Sodio-Calcio/metabolismo , Factores de TiempoRESUMEN
The role of K(+) channels in nitric oxide (NO)-induced vasorelaxation has been largely investigated in resistance vessels where iberiotoxin-sensitive MaxiK channels play a predominant role. However, the nature of the K(+) channel(s) involved in the relaxation triggered by NO-releasing compounds [nitroglycerin, NTG; NOR 3 [(+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide]] or atrial natriuretic peptide (ANP) in the conduit vessel aorta has remained elusive. We now demonstrate that, in rat aorta, the relaxation due to these vasorelaxants is not affected by the MaxiK channel blocker iberiotoxin (10(-7)-10(-6) M) as was the control vascular bed used (mesenteric artery). The inability of iberiotoxin to prevent NO/ANP-induced aortic relaxations was not due to lower expression of MaxiK in aorta or due to the predominance of iberiotoxin-resistant channels in this conduit vessel. Aortic relaxations were strongly diminished by 4-aminopyridine (4-AP) (> or =5 x 10(-3) M) or by tetraethylammonium (>2 x 10(-3) M) at concentrations known to inhibit voltage-dependent K(+) (K(v)) 2-type channels but not by other K(+) channel inhibitors, glibenclamide, apamin, charybdotoxin, tertiapin, or E-4031 N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl-]carbonyl]phenyl]methanesulfonamide dihydrochloride). Consistent with a role of K(v)2-type channels, K(v) currents in A7r5 aortic myocytes were stimulated by NTG and inhibited by > or =5 x 10(-3) M 4-AP. Furthermore, immunocytochemistry, immunoblot, and real-time polymerase chain reaction analyses confirmed the presence of K(v)2.1 channels in aorta. K(v)2.1 transcripts were approximately 100-fold more abundant than K(v)2.2. Our results support low-affinity 4-AP-sensitive K(v) channels, assembled at least partially by K(v)2.1 subunit, as downstream effectors of NO/ANP-signaling cascade regulating aortic vasorelaxation and further demonstrate vessel-specific K(+) channel involvement in NO/ANP-induced relaxation.
Asunto(s)
Aorta Torácica/fisiología , Factor Natriurético Atrial/fisiología , Arterias Mesentéricas/fisiología , Óxido Nítrico/fisiología , Canales de Potasio con Entrada de Voltaje/fisiología , Vasodilatación/fisiología , Animales , Aorta Torácica/efectos de los fármacos , Aorta Torácica/metabolismo , Factor Natriurético Atrial/metabolismo , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Membrana Celular/fisiología , Inhibidores Enzimáticos/farmacología , Guanilato Ciclasa , Immunoblotting , Técnicas In Vitro , Canales de Potasio de Gran Conductancia Activados por el Calcio/biosíntesis , Masculino , Arterias Mesentéricas/efectos de los fármacos , Arterias Mesentéricas/metabolismo , Óxido Nítrico/metabolismo , Donantes de Óxido Nítrico/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio con Entrada de Voltaje/antagonistas & inhibidores , Ratas , Ratas Sprague-Dawley , Ratas Wistar , Receptores Citoplasmáticos y Nucleares/antagonistas & inhibidores , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/efectos de los fármacos , Guanilil Ciclasa Soluble , Vasodilatación/efectos de los fármacosAsunto(s)
Calcio/análisis , Microscopía Confocal , Miocardio/química , Animales , Miocardio/citología , RatasRESUMEN
T-type Ca(2+) channels are present in cardiovascular, neuronal, and endocrine systems; and they are now receiving attention as novel therapeutic targets. Many drugs and compounds non-specificaly block T-type Ca(2+) channels. Certain dihydropyridine compounds, such as efonidipine, have blocking activity on both L-type and T-type Ca(2+) channels which possibly underlies their excellent clinical profiles such as minimum reflex tachycardia and renal protection. Selective inhibitors of T-type Ca(2+) channels, such as non-hydrolyzable mibefradil and R(-)-efonidipine, are powerful pharmacological tools for further studies and may lead to the development of novel therapeutic strategies.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo T/efectos de los fármacos , Diseño de Fármacos , Animales , Canales de Calcio Tipo L/efectos de los fármacos , Dihidropiridinas/farmacología , Humanos , Mibefradil/farmacología , Nitrofenoles/farmacología , Compuestos Organofosforados/farmacologíaRESUMEN
The functional role of the sodium-calcium exchanger in mouse ventricular myocardium was evaluated with a newly developed specific inhibitor, SEA0400. Contractile force and action potential configuration were measured in isolated ventricular tissue preparations, and cell shortening and Ca2+ transients were measured in indo-1-loaded isolated ventricular cardiomyocytes. SEA0400 increased the contractile force, cell shortening and Ca2+ transient amplitude, and shortened the late plateau phase of the action potential. alpha-adrenergic stimulation by phenylephrine produced a sustained decrease in contractile force, cell shortening and Ca2+ transient amplitude, which were all inhibited by SEA0400. Increasing the contraction frequency resulted in a decrease in contractile force in the absence of drugs (negative staircase phenomenon). This frequency-dependent decrease was attenuated by SEA0400 and enhanced by phenylephrine. Phenylephrine increased the Ca2+ sensitivity of contractile proteins in isolated ventricular cardiomyocytes, while SEA0400 had no effect. These results provide the first pharmacological evidence in the mouse ventricular myocardium that inward current generated by Ca2+ extrusion through the sodium-calcium exchanger during the Ca2+ transient contributes to the action potential late plateau, that alpha-adrenoceptor-mediated negative inotropy is produced by enhanced Ca2+ extrusion through the sodium-calcium exchanger, and that the negative staircase phenomenon can be explained by increased Ca2+ extrusion through the sodium-calcium exchanger at higher contraction frequencies.