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Voltage-dependent calcium (Ca2+) channels control a variety of physiological functions, such as excitation-contraction coupling in cardiac and smooth muscle, secretion of hormones and release of neurotransmitters.Studies on dissociated or cultured cells enabled us to compare their electrophysiological and pharmacological properties and their regulation in various tissues. Molecular genetics has provided a structural basis with which to observe the functional diversity of Ca2+ channels, which are composed of several subunits (α1, α2-δ, β, γ). Structure-function experiments, using expression in Xenopus oocytes, were designed to explain the molecular basis underlying this functional diversity. Six genes have been identified encoding the pore subunit (α1) which determines the basic profile, i.e. the pharmacology of any Ca2+ channel. However, using a reconstitution model, the auxiliary subunits, but mainly β subunits, for which four genes and several variants have been isolated, are able to modify the level of expression and the properties of a Ca2+ current directed by an α1 subunit. Our structure-function studies are mainly designed to investigate the functional consequences of α1—β interaction on electrophysiological and pharmacological properties, especially in the case of cardiovascular Ca2+ channels. These studies should lead to a better understanding of the molecular basis underlying the differences between cardiac and vascular Ca2+ channels and also their implication in pathophysiology. Functional expression of the various combinations of subunit isoforms and identification of the precise oligomeric structure of voltage-dependent Ca2+ channels in specific cell types should help in the development of new therapeutic drugs. [ABSTRACT FROM PUBLISHER]

Early studies in enzymatically isolated animal cardiomyocytes indicated the voltage-gated “L-type” Ca2+ currents (ICaL) can be upregulated following an increase of the frequency of activation. Recently, we evidenced a similar regulation of ICaL in human cardiomyocytes from both left and right ventricles and atria over a physiopathological range of stimulations (between 0.5 and 5 Hz). This regulation, enhanced by the β-adrenergic stimulation, may be involved in the frequency-dependent potentiation of cardiac contractile force in the human healthy myocardium. We show here that the frequency-dependent regulation of ICaL is controlled by the level of phosphorylation, as well as dephosphorylation, of the Ca2+ channels. It was enhanced following activation of the protein kinase A activated by intracellular cyclic AMP (cAMP). Therefore, we anticipate that all agents stimulating cAMP production will favor this process, which was demonstrated here by activating 5HT-4 receptors using serotonin. Alternatively, it was also enhanced by the phosphatase inhibitor okadaic acid which prevents Ca2+ channels dephosphorylation. Alteration or abnormal modulation by β-adrenergic receptor stimulation of the frequency-dependent facilitation of ICaL may partly explain the altered force-frequency relation described in heart failure. [ABSTRACT FROM AUTHOR]

We have used human β2 and β4 cDNA probes to map the genes encoding two isoforms of the regulatory β subunit of voltage-activated Ca2+ channels, viz. CACNB2 (β2) and CACNB4 (β4), to human chromosomes 10p12 and 2q22-q23, respectively, by fluorescence in situ hybridization. The gene encoding the β2 protein, first described as a Lambert-Eaton myasthenic syndrome (LEMS) antigen in humans, is found close to a region that undergoes chromosome rearrangements in small cell lung cancer, which occurs in association with LEMS. CACNB2 (β2) and CACNB4 (β4) genes are members of the ion-channel gene superfamily and it should now be possible to examine their loci by linkage analysis of ion-channel-related disorders. To date, no such disease-related gene has been assigned to 10p12 and 2q22-q23. [ABSTRACT FROM AUTHOR]

Introduction Sino-atrial node (SAN) pacemaker activity is generated by ion channels of the plasma membrane, such as hyperpolarization-activated “funny” f-(HCN), Ca 2+ channels and ryanodine receptor (RyR) – dependent Ca 2+ release from the sarcoplasmic reticulum (SR). It is currently disputed whether Ca 2+ release from RyRs could sustain viable pacemaker activity provided preserved SR Ca 2+ content. While working myocytes express L-type Ca v 1.2 channels to maintain SR Ca 2+ content, SAN cells express also L-type Ca v 1.3 and T-type Ca v 3.1 channels to generate pacemaking. Objectives We used mutant mice carrying concomitant ablation of Ca v 1.3 and Ca v 3.1 (Ca v 1.3 −/− /Ca v 3.1 −/− ) to study the importance of these channels in automaticity. We also investigated the role of f-HCN channels and RyR-dependent Ca 2+ release in residual pacemaker activity of mutant mice. Methods We employed in vivo telemetric recordings of heart rate (HR) in Ca v 1.3 −/− , Ca v 3.1 −/− and Ca v 1.3 −/− /Ca v 3.1 −/− mice. We studied the consequences of pharmacologic inhibition of f-HCN and TTX-sensitive Na + channels in mutant mice using Langendorff perfused hearts or optical mapping (OM) of the pacemaker impulse in intact SAN preparations (SANs). Results Ca v ablation reduced HR in mice: Ca v 3.1 −/− (−7.6%, n = 11), Ca v 1.3 −/− (−24.4%, n = 8), Ca v 1.3 −/− /Ca v 3.1 −/− (−35%, n = 11). In OM experiments on SANs, concomitant inhibition of f-HCN and Na v 1.1 channels slowed pacemaking in wild-type (−48%, n = 7) and Ca v 3.1 −/− (−37%, n = 7), while arresting automaticity in 4/6 of Ca v 1.3 −/− , 3/6 of Ca v 1.3 −/− /Ca v 3.1 −/− . When present, residual pacemaking was reduced by 82%. Similar results were obtained using isolated Ca v 1.3 −/− /Ca v 3.1 −/− pacemaker cells were automaticity arrested in 5/9 cells tested, or was reduced by 80% in 4/9 cells. Conclusion Heart automaticity is primarily generated by Ca v 1.3 and f-HCN channels. RyR-dependent Ca 2+ release cannot sustain automaticity following concomitant targeting of Ca v 1.3 and f-HCN channels. [ABSTRACT FROM AUTHOR]

Acute myocardial infarction (AMI) is the major cause of cardiovascular mortality worldwide. Early reperfusion is the only treatment recommended to reduce infarct size (IS). However, reperfusion presents also deleterious effects such as ischemia-reperfusion (IR) injury due to irreversible apoptotic death of cardiomyocytes. Most ischemic episodes are triggered by an increase in heart rate (HR) that induces an imbalance between myocardial oxygen delivery and consumption. The BEAUTIFUL clinical trial has demonstrated that moderate HR reduction diminishes the frequency of AMI episodes in patients with stable coronary artery disease and increased HR at rest. The HCN-mediated If current and the Cav1.3-mediated L-type Ca2+ currents play important roles in the generation of automaticity and HR, therefore they are interesting targets for selective control of HR and cardioprotection during AMI.The aim of our study was to investigate if targeting Cav1.3 channels could be an efficient strategy to reduce IS. Cav1.3 -/- mice was used as a genetic model of Cav1.3 inhibition because of the lack of selective blocker. Ivabradine, the selective f-channel blocker, was used for pure HR reduction as a positive control. Results show that selective HR decrease (40%) in an in vivo mouse model of acute MI is associated with reduced IR injury. Ivabradine administration 30 minutes before ischemia significantly reduced IS (35%). Cav1.3 -/- mice presented reduced IS (30%) compared to WT mice. In addition, preliminary results show that Girk4 -/- mice, a genetic model of moderate tachycardia (10%) displayed increased IS (45%) compared to control mice. In conclusion, results suggest a direct relationship between HR and IR injury and that inhibition of Cav1.3 channels constitutes a promising strategy to reduce both HR and IS. [ABSTRACT FROM AUTHOR]

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

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 Ca v 1.2 and Ca v 1.3 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 Ca v 1.2 -mediated L-type calcium currents (I CaL ) at concentrations leaving Ca v 1.3-mediated I CaL unaffected in both native cardiac myocytes and HEK-293T cells expressing recombinant Ca v 1.2 and Ca v 1.3 channels. Functionally, calciseptine potently inhibits cardiac contraction without altering the pacemaker activity in sino-atrial node cells, underscoring differential roles of Ca v 1.2- and Ca v 1.3 in cardiac contractility and automaticity. In summary, calciseptine is a selective L-type Ca v 1.2 Ca 2+ channel blocker and should be a valuable tool to dissect the role of these L-channel isoforms., (© 2024. The Author(s).)

Background: Acute myocardial infarction (AMI) is the major cause of cardiovascular mortality worldwide. Most ischemic episodes are triggered by an increase in heart rate, which induces an imbalance between myocardial oxygen delivery and consumption. Developing drugs that selectively reduce heart rate by inhibiting ion channels involved in heart rate control could provide more clinical benefits. The Ca v 1.3-mediated L-type Ca 2+ current ( I Cav1.3 ) play important roles in the generation of heart rate. Therefore, they can constitute relevant targets for selective control of heart rate and cardioprotection during AMI., Objective: We aimed to investigate the relationship between heart rate and infarct size using mouse strains knockout for Ca v 1.3 ( Ca v 1.3 -/- ) L-type calcium channel and of the cardiac G protein gated potassium channel ( Girk4 -/- ) in association with the funny (f)-channel inhibitor ivabradine., Methods: Wild-type (WT), Ca v 1.3 +/- , Ca v 1.3 -/- and Girk4 -/- mice were used as models of respectively normal heart rate, moderate heart rate reduction, bradycardia, and mild tachycardia, respectively. Mice underwent a surgical protocol of myocardial IR (40 min ischemia and 60 min reperfusion). Heart rate was recorded by one-lead surface ECG recording, and infarct size measured by triphenyl tetrazolium chloride staining. In addition, Ca v 1.3 -/- and WT hearts perfused on a Langendorff system were subjected to the same ischemia-reperfusion protocol ex vivo , without or with atrial pacing, and the coronary flow was recorded., Results: Ca v 1.3 -/- mice presented reduced infarct size (-29%), while Girk4 -/- displayed increased infarct size (+30%) compared to WT mice. Consistently, heart rate reduction in Ca v 1.3 +/- or by the f-channel blocker ivabradine was associated with significant decrease in infarct size (-27% and -32%, respectively) in comparison to WT mice., Conclusion: Our results show that decreasing heart rate allows to protect the myocardium against IR injury in vivo and reveal a close relationship between basal heart rate and IR injury. In addition, this study suggests that targeting Ca v 1.3 channels could constitute a relevant target for reducing infarct size, since maximal heart rate dependent cardioprotective effect is already observed in Ca v 1.3 +/- mice., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Delgado-Betancourt, Chinda, Mesirca, Barrere, Covinhes, Gallot, Vincent, Bidaud, Kumphune, Nargeot, Piot, Wickman, Mangoni and Barrère-Lemaire.)