RESUMEN
BACKGROUND: Ventricular arrhythmias (VAs) demonstrate a prominent day-night rhythm, commonly presenting in the morning. Transcriptional rhythms in cardiac ion channels accompany this phenomenon, but their role in the morning vulnerability to VAs and the underlying mechanisms are not understood. We investigated the recruitment of transcription factors that underpins transcriptional rhythms in ion channels and assessed whether this mechanism was pertinent to the heart's intrinsic diurnal susceptibility to VA. METHODS AND RESULTS: Assay for transposase-accessible chromatin with sequencing performed in mouse ventricular myocyte nuclei at the beginning of the animals' inactive (ZT0) and active (ZT12) periods revealed differentially accessible chromatin sites annotating to rhythmically transcribed ion channels and distinct transcription factor binding motifs in these regions. Notably, motif enrichment for the glucocorticoid receptor (GR; transcriptional effector of corticosteroid signaling) in open chromatin profiles at ZT12 was observed, in line with the well-recognized ZT12 peak in circulating corticosteroids. Molecular, electrophysiological, and in silico biophysically-detailed modeling approaches demonstrated GR-mediated transcriptional control of ion channels (including Scn5a underlying the cardiac Na+ current, Kcnh2 underlying the rapid delayed rectifier K+ current, and Gja1 responsible for electrical coupling) and their contribution to the day-night rhythm in the vulnerability to VA. Strikingly, both pharmacological block of GR and cardiomyocyte-specific genetic knockout of GR blunted or abolished ion channel expression rhythms and abolished the ZT12 susceptibility to pacing-induced VA in isolated hearts. CONCLUSIONS: Our study registers a day-night rhythm in chromatin accessibility that accompanies diurnal cycles in ventricular myocytes. Our approaches directly implicate the cardiac GR in the myocyte excitability rhythm and mechanistically link the ZT12 surge in glucocorticoids to intrinsic VA propensity at this time.
Asunto(s)
Ritmo Circadiano , Miocitos Cardíacos , Receptores de Glucocorticoides , Animales , Receptores de Glucocorticoides/metabolismo , Receptores de Glucocorticoides/genética , Ratones , Miocitos Cardíacos/metabolismo , Masculino , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/fisiopatología , Arritmias Cardíacas/genética , Ratones Endogámicos C57BL , Canal de Sodio Activado por Voltaje NAV1.5/metabolismo , Canal de Sodio Activado por Voltaje NAV1.5/genética , Conexina 43/metabolismo , Conexina 43/genética , Ratones Noqueados , Potenciales de AcciónRESUMEN
Sepsis has emerged as a global health burden associated with multiple organ dysfunction and 20% mortality rate in patients. Numerous clinical studies over the past two decades have correlated the disease severity and mortality in septic patients with impaired heart rate variability (HRV), as a consequence of impaired chronotropic response of sinoatrial node (SAN) pacemaker activity to vagal/parasympathetic stimulation. However, the molecular mechanism(s) downstream to parasympathetic inputs have not been investigated yet in sepsis, particularly in the SAN. Based on electrocardiography, fluorescence Ca2+ imaging, electrophysiology, and protein assays from organ to subcellular level, we report that impaired muscarinic receptor subtype 2-G protein-activated inwardly-rectifying potassium channel (M2R-GIRK) signaling in a lipopolysaccharide-induced proxy septic mouse model plays a critical role in SAN pacemaking and HRV. The parasympathetic responses to a muscarinic agonist, namely IKACh activation in SAN cells, reduction in Ca2+ mobilization of SAN tissues, lowering of heart rate and increase in HRV, were profoundly attenuated upon lipopolysaccharide-induced sepsis. These functional alterations manifested as a direct consequence of reduced expression of key ion-channel components (GIRK1, GIRK4, and M2R) in the mouse SAN tissues and cells, which was further evident in the human right atrial appendages of septic patients and likely not mediated by the common proinflammatory cytokines elevated in sepsis.
Asunto(s)
Lipopolisacáridos , Sepsis , Humanos , Animales , Ratones , Lipopolisacáridos/toxicidad , Lipopolisacáridos/metabolismo , Nodo Sinoatrial/fisiología , Canales de Potasio Rectificados Internamente Asociados a la Proteína G/genética , Canales de Potasio Rectificados Internamente Asociados a la Proteína G/metabolismo , Transducción de Señal/fisiología , Sepsis/inducido químicamente , Sepsis/metabolismoRESUMEN
Encoded by ANK2, ankyrin-B (AnkB) is a multifunctional adapter protein critical for the expression and targeting of key cardiac ion channels, transporters, cytoskeletal-associated proteins, and signaling molecules. Mice deficient for AnkB expression are neonatal lethal, and mice heterozygous for AnkB expression display cardiac structural and electrical phenotypes. Human ANK2 loss-of-function variants are associated with diverse cardiac manifestations; however, human clinical 'AnkB syndrome' displays incomplete penetrance. To date, animal models for human arrhythmias have generally been knock-out or transgenic overexpression models and thus the direct impact of ANK2 variants on cardiac structure and function in vivo is not clearly defined. Here, we directly tested the relationship of a single human ANK2 disease-associated variant with cardiac phenotypes utilizing a novel in vivo animal model. At baseline, young AnkBp.E1458G+/+ mice lacked significant structural or electrical abnormalities. However, aged AnkBp.E1458G+/+ mice displayed both electrical and structural phenotypes at baseline including bradycardia and aberrant heart rate variability, structural remodeling, and fibrosis. Young and old AnkBp.E1458G+/+ mice displayed ventricular arrhythmias following acute (adrenergic) stress. In addition, young AnkBp.E1458G+/+ mice displayed structural remodeling following chronic (transverse aortic constriction) stress. Finally, AnkBp.E1458G+/+ myocytes harbored alterations in expression and/or localization of key AnkB-associated partners, consistent with the underlying disease mechanism. In summary, our findings illustrate the critical role of AnkB in in vivo cardiac function as well as the impact of single AnkB loss-of-function variants in vivo. However, our findings illustrate the contribution and in fact necessity of secondary factors (aging, adrenergic challenge, pressure-overload) to phenotype penetrance and severity.
Asunto(s)
Ancirinas , Miocitos Cardíacos , Animales , Humanos , Ratones , Adrenérgicos/metabolismo , Ancirinas/metabolismo , Modelos Animales de Enfermedad , Canales Iónicos/metabolismo , Ratones Noqueados , Miocitos Cardíacos/metabolismo , Fenotipo , Envejecimiento/metabolismoRESUMEN
The spontaneous activity of the sinoatrial node initiates the heartbeat. Sino-atrial node dysfunction (SND) and sick sinoatrial (sick sinus) syndrome are caused by the heart's inability to generate a normal sinoatrial node action potential. In clinical practice, SND is generally considered an age-related pathology, secondary to degenerative fibrosis of the heart pacemaker tissue. However, other forms of SND exist, including idiopathic primary SND, which is genetic, and forms that are secondary to cardiovascular or systemic disease. The incidence of SND in the general population is expected to increase over the next half century, boosting the need to implant electronic pacemakers. During the last two decades, our knowledge of sino-atrial node physiology and of the pathophysiological mechanisms underlying SND has advanced considerably. This review summarizes the current knowledge about SND mechanisms and discusses the possibility of introducing new pharmacologic therapies for treating SND.
Asunto(s)
Síndrome del Seno Enfermo , Nodo Sinoatrial , Sistema de Conducción Cardíaco , HumanosRESUMEN
Human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes raise the possibility of generating pluripotent stem cells from a wide range of human diseases. In the cardiology field, hiPSCs have been used to address the mechanistic bases of primary arrhythmias and in investigations of drug safety. These studies have been focused primarily on atrial and ventricular pathologies. Consequently, many hiPSC-based cardiac differentiation protocols have been developed to differentiate between atrial- or ventricular-like cardiomyocytes. Few protocols have successfully proposed ways to obtain hiPSC-derived cardiac pacemaker cells, despite the very limited availability of human tissues from the sinoatrial node. Providing an in vitro source of pacemaker-like cells would be of paramount importance in terms of furthering our understanding of the mechanisms underlying sinoatrial node pathophysiology and testing innovative clinical strategies against sinoatrial node dysfunction (i.e., biological pacemakers and genetic- and pharmacological- based therapy). Here, we summarize and detail the currently available protocols used to obtain patient-derived pacemaker-like cells.
Asunto(s)
Células Madre Pluripotentes Inducidas , Células Madre Pluripotentes , Humanos , Miocitos Cardíacos , Diferenciación Celular/fisiología , Nodo SinoatrialRESUMEN
[Figure: see text].
Asunto(s)
Potenciales de Acción , Bloqueo Atrioventricular/metabolismo , Nodo Atrioventricular/metabolismo , Canales de Calcio Tipo L/metabolismo , Frecuencia Cardíaca , Canales Regulados por Nucleótidos Cíclicos Activados por Hiperpolarización/metabolismo , Miocitos Cardíacos/metabolismo , Resistencia Física , Animales , Bloqueo Atrioventricular/inducido químicamente , Bloqueo Atrioventricular/diagnóstico , Bloqueo Atrioventricular/fisiopatología , Nodo Atrioventricular/fisiopatología , Atropina , Biopsia , Canales de Calcio Tipo L/genética , Modelos Animales de Enfermedad , Electrocardiografía , Caballos , Canales Regulados por Nucleótidos Cíclicos Activados por Hiperpolarización/genética , Masculino , Ratones Endogámicos C57BL , MicroARNs/genética , MicroARNs/metabolismo , Condicionamiento Físico Animal , Propranolol , Natación , Transcripción GenéticaRESUMEN
Cardiac arrhythmias are a major cause of death and disability. A large number of experimental cell and animal models have been developed to study arrhythmogenic diseases. These models have provided important insights into the underlying arrhythmia mechanisms and translational options for their therapeutic management. This position paper from the ESC Working Group on Cardiac Cellular Electrophysiology provides an overview of (i) currently available in vitro, ex vivo, and in vivo electrophysiological research methodologies, (ii) the most commonly used experimental (cellular and animal) models for cardiac arrhythmias including relevant species differences, (iii) the use of human cardiac tissue, induced pluripotent stem cell (hiPSC)-derived and in silico models to study cardiac arrhythmias, and (iv) the availability, relevance, limitations, and opportunities of these cellular and animal models to recapitulate specific acquired and inherited arrhythmogenic diseases, including atrial fibrillation, heart failure, cardiomyopathy, myocarditis, sinus node, and conduction disorders and channelopathies. By promoting a better understanding of these models and their limitations, this position paper aims to improve the quality of basic research in cardiac electrophysiology, with the ultimate goal to facilitate the clinical translation and application of basic electrophysiological research findings on arrhythmia mechanisms and therapies.
Asunto(s)
Fibrilación Atrial , Técnicas Electrofisiológicas Cardíacas , Animales , Electrofisiología Cardíaca , Fenómenos Electrofisiológicos , Humanos , Modelos TeóricosRESUMEN
Ryanodine receptors are responsible for the massive release of calcium from the sarcoplasmic reticulum that triggers heart muscle contraction. Maurocalcin (MCa) is a 33 amino acid peptide toxin known to target skeletal ryanodine receptor. We investigated the effect of MCa and its analog MCaE12A on isolated cardiac ryanodine receptor (RyR2), and showed that they increase RyR2 sensitivity to cytoplasmic calcium concentrations promoting channel opening and decreases its sensitivity to inhibiting calcium concentrations. By measuring intracellular Ca2+ transients, calcium sparks and contraction on cardiomyocytes isolated from adult rats or differentiated from human-induced pluripotent stem cells, we demonstrated that MCaE12A passively penetrates cardiomyocytes and promotes the abnormal opening of RyR2. We also investigated the effect of MCaE12A on the pacemaker activity of sinus node cells from different mice lines and showed that, MCaE12A improves pacemaker activity of sinus node cells obtained from mice lacking L-type Cav1.3 channel, or following selective pharmacologic inhibition of calcium influx via Cav1.3. Our results identify MCaE12A as a high-affinity modulator of RyR2 and make it an important tool for RyR2 structure-to-function studies as well as for manipulating Ca2+ homeostasis and dynamic of cardiac cells.
Asunto(s)
Calcio/metabolismo , Miocitos Cardíacos/efectos de los fármacos , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Venenos de Escorpión/farmacología , Nodo Sinoatrial/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Animales , Señalización del Calcio/efectos de los fármacos , Citoplasma/efectos de los fármacos , Citoplasma/metabolismo , Homeostasis , Humanos , Masculino , Ratones , Ratones Noqueados , Miocitos Cardíacos/metabolismo , Células Madre Pluripotentes , Ratas , Ratas Wistar , Retículo Sarcoplasmático/efectos de los fármacos , Retículo Sarcoplasmático/metabolismo , Venenos de Escorpión/química , Nodo Sinoatrial/citología , Nodo Sinoatrial/fisiología , PorcinosRESUMEN
The heart automaticity is a fundamental physiological function in vertebrates. The cardiac impulse is generated in the sinus node by a specialized population of spontaneously active myocytes known as "pacemaker cells." Failure in generating or conducting spontaneous activity induces dysfunction in cardiac automaticity. Several families of ion channels are involved in the generation and regulation of the heart automaticity. Among those, voltage-gated L-type Cav1.3 (α1D) and T-type Cav3.1 (α1G) Ca2+ channels play important roles in the spontaneous activity of pacemaker cells. Ca2+ channel channelopathies specifically affecting cardiac automaticity are considered rare. Recent research on familial disease has identified mutations in the Cav1.3-encoding CACNA1D gene that underlie congenital sinus node dysfunction and deafness (OMIM # 614896). In addition, both Cav1.3 and Cav3.1 channels have been identified as pathophysiological targets of sinus node dysfunction and heart block, caused by congenital autoimmune disease of the cardiac conduction system. The discovery of channelopathies linked to Cav1.3 and Cav3.1 channels underscores the importance of Ca2+ channels in the generation and regulation of heart's automaticity.
Asunto(s)
Canales de Calcio Tipo L/genética , Canales de Calcio Tipo L/metabolismo , Canales de Calcio Tipo T/genética , Canales de Calcio Tipo T/metabolismo , Canalopatías/genética , Canalopatías/metabolismo , Miocitos Cardíacos/metabolismo , Animales , Arritmias Cardíacas/genética , Arritmias Cardíacas/metabolismo , Frecuencia Cardíaca/genética , Humanos , Nodo Sinoatrial/metabolismo , Nodo Sinoatrial/patologíaRESUMEN
The above article was published online with an error in Fig. 1b. There is a doubled action potential at the far right of the left panel of the figure.
RESUMEN
Dysfunction of pacemaker activity in the sinoatrial node (SAN) underlies "sick sinus" syndrome (SSS), a common clinical condition characterized by abnormally low heart rate (bradycardia). If untreated, SSS carries potentially life-threatening symptoms, such as syncope and end-stage organ hypoperfusion. The only currently available therapy for SSS consists of electronic pacemaker implantation. Mice lacking L-type Cav1.3 Ca(2+) channels (Cav1.3(-/-)) recapitulate several symptoms of SSS in humans, including bradycardia and atrioventricular (AV) dysfunction (heart block). Here, we tested whether genetic ablation or pharmacological inhibition of the muscarinic-gated K(+) channel (IKACh) could rescue SSS and heart block in Cav1.3(-/-) mice. We found that genetic inactivation of IKACh abolished SSS symptoms in Cav1.3(-/-) mice without reducing the relative degree of heart rate regulation. Rescuing of SAN and AV dysfunction could be obtained also by pharmacological inhibition of IKACh either in Cav1.3(-/-) mice or following selective inhibition of Cav1.3-mediated L-type Ca(2+) (ICa,L) current in vivo. Ablation of IKACh prevented dysfunction of SAN pacemaker activity by allowing net inward current to flow during the diastolic depolarization phase under cholinergic activation. Our data suggest that patients affected by SSS and heart block may benefit from IKACh suppression achieved by gene therapy or selective pharmacological inhibition.
Asunto(s)
Canales de Calcio Tipo L/efectos de los fármacos , Proteínas de Unión al GTP/fisiología , Bloqueo Cardíaco/tratamiento farmacológico , Activación del Canal Iónico/fisiología , Síndrome del Seno Enfermo/tratamiento farmacológico , Animales , Canales de Calcio Tipo L/genética , Canales de Calcio Tipo L/fisiología , Humanos , Ratones , Ratones NoqueadosRESUMEN
Pacemaker activity of the sino-atrial node generates the heart rate. Disease of the sinus node and impairment of atrioventricular conduction induce an excessively low ventricular rate (bradycardia), which cannot meet the needs of the organism. Bradycardia accounts for about half of the total workload of clinical cardiologists. The 'sick sinus' syndrome (SSS) is characterized by sinus bradycardia and periods of intermittent atrial fibrillation. Several genetic or acquired risk factors or pathologies can lead to SSS. Implantation of an electronic pacemaker constitutes the only available therapy for SSS. The incidence of SSS is forecast to double over the next 50 years, with ageing of the general population thus urging the development of complementary or alternative therapeutic strategies. In recent years an increasing number of mutations affecting ion channels involved in sino-atrial automaticity have been reported to underlie inheritable SSS. L-type Cav 1.3 channels play a major role in the generation and regulation of sino-atrial pacemaker activity and atrioventricular conduction. Mutation in the CACNA1D gene encoding Cav 1.3 channels induces loss-of-function in channel activity and underlies the sino-atrial node dysfunction and deafness syndrome (SANDD). Mice lacking Cav 1.3 channels (Cav 1.3-/- ) fairly recapitulate SSS and constitute a precious model to test new therapeutic approaches to handle this disease. Work in our laboratory shows that targeting G protein-gated K+ (IKACh ) channels effectively rescues SSS of Cav 1.3-/- mice. This new concept of 'compensatory' ion channel targeting shines new light on the principles underlying the pacemaker mechanism and may open the way to new therapies for SSS.
Asunto(s)
Canales de Calcio Tipo L/metabolismo , Canalopatías/metabolismo , Ventrículos Cardíacos/metabolismo , Animales , Bradicardia/genética , Bradicardia/metabolismo , Bradicardia/fisiopatología , Canales de Calcio Tipo L/genética , Canalopatías/genética , Canalopatías/fisiopatología , Frecuencia Cardíaca/genética , Frecuencia Cardíaca/fisiología , Ventrículos Cardíacos/fisiopatología , Humanos , Mutación/genética , Síndrome del Seno Enfermo/genética , Síndrome del Seno Enfermo/metabolismo , Síndrome del Seno Enfermo/fisiopatología , Nodo Sinoatrial/metabolismo , Nodo Sinoatrial/fisiopatologíaRESUMEN
Sick sinus syndrome and atrioventricular block are common clinical problems, often necessitating permanent pacemaker placement, yet the pathophysiology of these conditions remains poorly understood. Here we show that Transient Receptor Potential Melastatin 7 (TRPM7), a divalent-permeant channel-kinase of unknown function, is highly expressed in embryonic myocardium and sinoatrial node (SAN) and is required for cardiac automaticity in these specialized tissues. TRPM7 disruption in vitro, in cultured embryonic cardiomyocytes, significantly reduces spontaneous Ca(2+) transient firing rates and is associated with robust down-regulation of Hcn4, Cav3.1, and SERCA2a mRNA. TRPM7 knockdown in zebrafish, global murine cardiac Trpm7 deletion (KO(αMHC-Cre)), and tamoxifen-inducible SAN restricted Trpm7 deletion (KO(HCN4-CreERT2)) disrupts cardiac automaticity in vivo. Telemetered and sedated KO(αMHC-Cre) and KO(HCN4-CreERT2) mice show episodes of sinus pauses and atrioventricular block. Isolated SAN from KO(αMHC-Cre) mice exhibit diminished Ca(2+) transient firing rates with a blunted diastolic increase in Ca(2+). Action potential firing rates are diminished owing to slower diastolic depolarization. Accordingly, Hcn4 mRNA and the pacemaker current, I(f), are diminished in SAN from both KO(αMHC-Cre) and KO(HCN4-CreERT2) mice. Moreover, heart rates of KO(αMHC-Cre) mice are less sensitive to the selective I(f) blocker ivabradine, and acute application of the recently identified TRPM7 blocker FTY720 has no effect on action potential firing rates of wild-type SAN cells. We conclude that TRPM7 influences diastolic membrane depolarization and automaticity in SAN indirectly via regulation of Hcn4 expression.
Asunto(s)
Corazón/fisiología , Miocardio/metabolismo , Miocitos Cardíacos/fisiología , Canales Catiónicos TRPM/metabolismo , Animales , Calcio/metabolismo , Células Cultivadas , Canales Catiónicos Regulados por Nucleótidos Cíclicos/genética , Canales Catiónicos Regulados por Nucleótidos Cíclicos/metabolismo , Expresión Génica , Técnicas de Silenciamiento del Gen , Corazón/embriología , Frecuencia Cardíaca/genética , Frecuencia Cardíaca/fisiología , Canales Regulados por Nucleótidos Cíclicos Activados por Hiperpolarización , Potenciales de la Membrana/genética , Potenciales de la Membrana/fisiología , Ratones , Ratones Noqueados , Microscopía Confocal , Miocardio/citología , Miocitos Cardíacos/citología , Miocitos Cardíacos/metabolismo , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Nodo Sinoatrial/citología , Nodo Sinoatrial/embriología , Canales Catiónicos TRPM/genética , Pez Cebra/embriología , Pez Cebra/genética , Pez Cebra/fisiología , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/metabolismoRESUMEN
The sense of touch allows an organism to detect and respond to physical environmental stimuli. Mechanosensitive proteins play a crucial role in this process by converting the mechanical cue into a biological response. Recently, the Piezo family of stretch-activated ion channels has been identified as genuine mechanosensitive proteins. We set out to determine whether any of these genes are involved in touch response during zebrafish development. In situ hybridization indicates that piezo2b is specifically expressed in a subset of neurons (Rohon-Beard cells) responsible for detecting light touch. Using morpholino-mediated knockdown, we specifically targeted piezo2b and determined that it is involved in mediating touch-evoked response.
Asunto(s)
Canales Iónicos/metabolismo , Tacto , Proteínas de Pez Cebra/metabolismo , Animales , Canales Iónicos/antagonistas & inhibidores , Canales Iónicos/genética , Morfolinos/farmacología , Neuronas/metabolismo , Neuronas/fisiología , Pez Cebra , Proteínas de Pez Cebra/antagonistas & inhibidores , Proteínas de Pez Cebra/genéticaRESUMEN
BACKGROUND: Transient receptor potential (TRP) channels are a superfamily of broadly expressed ion channels with diverse physiological roles. TRPC1, TRPC3, and TRPC6 are believed to contribute to cardiac hypertrophy in mouse models. Human mutations in TRPM4 have been linked to progressive familial heart block. TRPM7 is a divalent-permeant channel and kinase of unknown function, recently implicated in the pathogenesis of atrial fibrillation; however, its function in ventricular myocardium remains unexplored. METHODS AND RESULTS: We generated multiple cardiac-targeted knockout mice to test the hypothesis that TRPM7 is required for normal ventricular function. Early cardiac Trpm7 deletion (before embryonic day 9; TnT/Isl1-Cre) results in congestive heart failure and death by embryonic day 11.5 as a result of hypoproliferation of the compact myocardium. Remarkably, Trpm7 deletion late in cardiogenesis (about embryonic day 13; αMHC-Cre) produces viable mice with normal adult ventricular size, function, and myocardial transcriptional profile. Trpm7 deletion at an intermediate time point results in 50% of mice developing cardiomyopathy associated with heart block, impaired repolarization, and ventricular arrhythmias. Microarray analysis reveals elevations in transcripts of hypertrophy/remodeling genes and reductions in genes important for suppressing hypertrophy (Hdac9) and for ventricular repolarization (Kcnd2) and conduction (Hcn4). These transcriptional changes are accompanied by action potential prolongation and reductions in transient outward current (Ito; Kcnd2). Similarly, the pacemaker current (If; Hcn4) is suppressed in atrioventricular nodal cells, accounting for the observed heart block. CONCLUSIONS: Trpm7 is dispensable in adult ventricular myocardium under basal conditions but is critical for myocardial proliferation during early cardiogenesis. Loss of Trpm7 at an intermediate developmental time point alters the myocardial transcriptional profile in adulthood, impairing ventricular function, conduction, and repolarization.
Asunto(s)
Eliminación de Gen , Sistema de Conducción Cardíaco/fisiología , Miocardio/citología , Miocitos Cardíacos/fisiología , Canales Catiónicos TRPM/deficiencia , Función Ventricular/fisiología , Potenciales de Acción/fisiología , Factores de Edad , Animales , Ratones , Ratones de la Cepa 129 , Ratones Noqueados , Canales Catiónicos TRPM/genética , Factores de TiempoRESUMEN
Cardiac automaticity is a fundamental physiological function in vertebrates. Heart rate is under the control of several neurotransmitters and hormones and is permanently adjusted by the autonomic nervous system to match the physiological demand of the organism. Several classes of ion channels and proteins involved in intracellular Ca(2+) handling contribute to pacemaker activity. Voltage-dependent T-type Ca(2+) channels are an integral part of the complex mechanism underlying pacemaking. T-type channels also contribute to impulse conduction in mice and humans. Strikingly, T-type channel isoforms are co-expressed in the cardiac conduction system with other ion channels that play a major role in pacemaking such as f- (HCN4) and L-type Cav1.3 channels. Pharmacologic inhibition of T-type channels reduces the spontaneous activity of isolated pacemaker myocytes of the sino-atrial node, the dominant heart rhythmogenic centre. Target inactivation of T-type Cav3.1 channels abolishes I Ca,T in both sino-atrial and atrioventricular myocytes and reduces the daily heart rate of freely moving mice. Cav3.1 channels contribute also to automaticity of the atrioventricular node and to ventricular escape rhythms, thereby stressing the importance of these channels in automaticity of the whole cardiac conduction system. Accordingly, loss-of-function of Cav3.1 channels contributes to severe form of congenital bradycardia and atrioventricular block in paediatric patients.
Asunto(s)
Nodo Atrioventricular/fisiología , Canales de Calcio Tipo T/fisiología , Frecuencia Cardíaca/fisiología , Nodo Sinoatrial/fisiología , Potenciales de Acción/fisiología , Animales , Arritmias Cardíacas/diagnóstico , Arritmias Cardíacas/fisiopatología , Síndrome de Brugada , Trastorno del Sistema de Conducción Cardíaco , Sistema de Conducción Cardíaco/anomalías , Sistema de Conducción Cardíaco/fisiología , Sistema de Conducción Cardíaco/fisiopatología , HumanosRESUMEN
Mechanosensitivity is an inherent property of virtually all cell types, allowing them to sense and respond to physical environmental stimuli. Stretch-activated ion channels represent a class of mechanosensitive proteins which allow cells to respond rapidly to changes in membrane tension; however their identity has remained elusive. The piezo genes have recently been identified as a family of stretch-activated mechanosensitive ion channels. We set out to determine the role of piezo1 during zebrafish development. Here we report that morpholino-mediated knockdown of piezo1 impairs erythrocyte survival without affecting hematopoiesis or differentiation. Our results demonstrate that piezo1 is involved in erythrocyte volume homeostasis, disruption of which results in swelling/lysis of red blood cells and consequent anemia.
Asunto(s)
Volumen de Eritrocitos/genética , Homeostasis/genética , Canales Iónicos/genética , Proteínas de Pez Cebra/genética , Pez Cebra/sangre , Pez Cebra/genética , Animales , Eritropoyesis/genética , Regulación del Desarrollo de la Expresión Génica , Técnicas de Silenciamiento del Gen , Canales Iónicos/metabolismo , Pez Cebra/embriología , Proteínas de Pez Cebra/metabolismoRESUMEN
Bradyarrhythmias including sinus bradycardia and atrioventricular (AV) block are frequently encountered in endurance athletes especially at night. While these are well tolerated by the young athlete, there is evidence that generally from the fifth decade of life onward, such arrhythmias can degenerate into pathological symptomatic bradycardia requiring pacemaker therapy. For many years, athletic bradycardia and AV block have been attributed to high vagal tone, but work from our group has questioned this widely held assumption and demonstrated a role for intrinsic electrophysiological remodeling of the sinus node and the AV node. In this article, we argue that bradyarrhythmias in the veteran athlete arise from the cumulative effects of exercise training, the circadian rhythm and aging on the electrical activity of the nodes. We consider contemporary strategies for the treatment of symptomatic bradyarrhythmias in athletes and highlight potential therapies resulting from our evolving mechanistic understanding of this phenomenon.
Asunto(s)
Atletas , Bradicardia , Humanos , Bradicardia/terapia , Bradicardia/fisiopatología , Bradicardia/etiología , Bradicardia/diagnóstico , Frecuencia Cardíaca/fisiología , ElectrocardiografíaRESUMEN
L-type voltage-gated calcium channels are involved in multiple physiological functions. Currently available antagonists do not discriminate between L-type channel isoforms. Importantly, no selective blocker is available to dissect the role of L-type isoforms Cav1.2 and Cav1.3 that are concomitantly co-expressed in the heart, neuroendocrine and neuronal cells. Here we show that calciseptine, a snake toxin purified from mamba venom, selectively blocks Cav1.2 -mediated L-type calcium currents (ICaL) at concentrations leaving Cav1.3-mediated ICaL unaffected in both native cardiac myocytes and HEK-293T cells expressing recombinant Cav1.2 and Cav1.3 channels. Functionally, calciseptine potently inhibits cardiac contraction without altering the pacemaker activity in sino-atrial node cells, underscoring differential roles of Cav1.2- and Cav1.3 in cardiac contractility and automaticity. In summary, calciseptine is a selective L-type Cav1.2 Ca2+ channel blocker and should be a valuable tool to dissect the role of these L-channel isoforms.