Ca2+-activated Cl− current is antiarrhythmic by reducing both spatial and temporal heterogeneity of cardiac repolarization

Abstract

The role of Ca2+-activated Cl− current (ICl(Ca)) in cardiac arrhythmias is still controversial. It can generate delayed afterdepolarizations in Ca2+-overloaded cells while in other studies incidence of early afterdepolarization (EAD) was reduced by ICl(Ca). Therefore our goal was to examine the role of ICl(Ca) in spatial and temporal heterogeneity of cardiac repolarization and EAD formation. Experiments were performed on isolated canine cardiomyocytes originating from various regions of the left ventricle; subepicardial, midmyocardial and subendocardial cells, as well as apical and basal cells of the midmyocardium. ICl(Ca) was blocked by 0.5 mmol/L 9-anthracene carboxylic acid (9-AC). Action potential (AP) changes were tested with sharp microelectrode recording. Whole-cell 9-AC-sensitive current was measured with either square pulse voltage-clamp or AP voltage-clamp (APVC). Protein expression of TMEM16A and Bestrophin-3, ion channel proteins mediating ICl(Ca), was detected by Western blot. 9-AC reduced phase-1 repolarization in every tested cell. 9-AC also increased AP duration in a reverse rate-dependent manner in all cell types except for subepicardial cells. Neither ICl(Ca) density recorded with square pulses nor the normalized expressions of TMEM16A and Bestrophin-3 proteins differed significantly among the examined groups of cells. The early outward component of ICl(Ca) was significantly larger in subepicardial than in subendocardial cells in APVC setting. Applying a typical subepicardial AP as a command pulse resulted in a significantly larger early outward component in both subepicardial and subendocardial cells, compared to experiments when a typical subendocardial AP was applied. Inhibiting ICl(Ca) by 9-AC generated EADs at low stimulation rates and their incidence increased upon beta-adrenergic stimulation. 9-AC increased the short-term variability of repolarization also. We suggest a protective role for ICl(Ca) against risk of arrhythmias by reducing spatial and temporal heterogeneity of cardiac repolarization and EAD formation.

β-adrenergic regulation of late Na+ current during cardiac action potential is mediated by both PKA and CaMKII

“…Rabbits were first injected with heparin (1000 U/kg) and then anesthetized with isoflurane inhalation (3–5%). After achieving deep anesthesia, a standard enzymatic technique was used to isolate ventricular myocytes at 37°C as previously described [33, 34]. Briefly, hearts were mounted on a Langendorff system and retrogradely perfused for 5 min with an oxygenated solution containing (in mmol/L): NaCl 138, KCl 5.4, CaCl 2 0.05, MgCl 2 1, NaH 2 PO 4 0.33, NaHCO 3 10, HEPES 10, glucose 6, pyruvic acid 2.5; at pH=7.4.…”

Late sodium current in human, canine and guinea pig ventricular myocardium

“…Single canine and human myocytes were obtained by enzymatic dispersion using the segment perfusion technique, as described previously [27]. Briefly, a wedge-shaped section of the ventricular wall supplied by the left anterior descending coronary artery was cannulated, dissected and perfused with a nominally Ca 2+ -free Joklik solution (Minimum Essential Medium Eagle, Joklik Modification, Sigma-Aldrich Co. St. Louis, MO, USA) for 5 min.…”

The transient receptor potential melastatin 4 channel inhibitor 9‐phenanthrol modulates cardiac sodium channel

“…Furthermore, a recent study indicated that 9‐phenanthrol can also inhibit the Ca 2+ ‐activated Cl − current conducted by the TMEM16A channel (Burris et al, ). However, this current contributes to phase 1 repolarization, inhibition of which may prolong APD and facilitate the occurrence of EADs (Hegyi et al, ). As a result, it is unlikely that the antiarrhythmic effect of 9‐phenanthrol is due to TMEM16A channel inhibition.…”