Calmodulin kinase II and protein kinase C mediate the effect of increased intracellular calcium to augment late sodium current in rabbit ventricular myocytes

Abstract

[Ca 2ϩ ]i from 0.1 to 0.3, 0.6, and 1.0 M increased I Na.L in a concentration-dependent manner from 0.221 Ϯ 0.038 to 0.554 Ϯ 0.045 pA/pF (n ϭ 10, P Ͻ 0.01) and was associated with an increase in mean Na ϩ channel open probability and prolongation of channel mean open-time (n ϭ 7, P Ͻ 0.01). In the presence of 0.6 M [Ca 2ϩ ]i, KN-93 (10 M) and bisindolylmaleimide (BIM, 2 M) decreased I Na.L by 45.2 and 54.8%, respectively. The effects of KN-93 and autocamtide-2-related inhibitory peptide II (2 M) were not different. A combination of overload, is a pathological occurrence in the heart and is reported to be related to ischemia, hypoxia, oxidative stress, cardiac hypertrophy, heart failure, and elevated catecholamine levels (7,11,28,35,49). Intracellular Ca 2ϩ overload results in cardiac mechanical and electrical dysfunction (44). Many pathological conditions that lead to intracellular Ca 2ϩ overload in ventricular myocytes are also associated with an increase in the late or persistent sodium current (I Na.L ) (1, 17, 18, 21, 23, 24, 26, 40 -42, 47, 48, 53). I Na.L is created when inactivation-resistant sodium channels continue to open for long periods during the action potential plateau. Maltsev et al. (25) reported that an increase in the level of [Ca 2ϩ ] i from baseline to 1 M increased the amplitude of I Na.L in dog ventricular myocytes via a mechanism involving activation of Ca 2ϩ -calmodulin-dependent protein kinase II (CaMKII). Elevated [Ca 2ϩ ] i is also reported to activate protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) (31, 39, 52), and the PKC activation is associated with an increase in I Na.L (3,4,10,14,27,29,48,50,51).An increase in the amplitude of I Na.L may prolong action potential duration, increase the transmural dispersion of repolarization, and cause cardiac arrhythmias (2). An increase in I Na.L also raises the intracellular sodium concentration and subsequently increases [Ca 2ϩ ] i via the reverse mode of the Na ϩ -Ca 2ϩ exchanger to cause further Ca 2ϩ influx (18,20). Reduction of the extracellular Na ϩ concentration or inhibition of I Na.L was shown to attenuate the increase in [Ca 2ϩ ] i (8,12,15,22,32,36,37,43). Inhibition of I Na.L is therefore a potential therapeutic target for the treatment of cardiac arrhythmias and myocardial dysfunction associated with intracellular Ca 2ϩ overload (5,6,16,33,34,45,46). In this study we tested the hypothesis that both CaMKII and PKC mediate the augmentation of I Na.L in the presence of an increased [Ca 2ϩ ] i . Using rabbit ventricular myocytes, we measured whole cell Na ϩ current and single Na ϩ channel activities, the latter with a novel open cell-attached patch technique. I Na.L and single Na ϩ channel activities were investigated under conditions mimicking the physiological and pathological conditions of normal and increased [Ca 2ϩ ] i . In cells with increased [Ca 2ϩ ] i , agents that modulate the functions of CaMKII, PKC, and MAPK were used to determine the relative contributions of these signali...

Post-translational modifications of the cardiac Na channel: contribution of CaMKII-dependent phosphorylation to acquired arrhythmias

“…Indeed, it is conceivable that increased PKC activity fuels an increase in mitochondrial ROS, which constitutively activate CaMKII to regulate I Na . Both CaMKII and PKC appeared to be involved in the Ca-dependent increase in I Na,L observed in rabbit cardiomyocytes (63).…”

Voltage-Gated Sodium Channel Phosphorylation at Ser571 Regulates Late Current, Arrhythmia, and Cardiac Function In Vivo

“…24 Among its numerous targets, CaMKII phosphorylates Na v to regulate the magnitude of I Na,L , as well as other properties including steady-state inactivation and recovery from inactivation. 21, 25–28 Although the molecular mechanism remains under investigation, several potential sites for CaMKII phosphorylation have been identified in the DI-DII linker of Na v 1.5, the predominant cardiac Na v alpha subunit. 22, 26, 29, 30 Na v 1.5 Ser571 first emerged as a potential CaMKII phosphorylation site from a functional screen in heterologous cells.…”

An Emerging Antiarrhythmic Target: Late Sodium Current

“…Resultantly, CaMKII upregulation facilitates INa,L that is reversible with CaMKII inhibitors. The link between increased CaMKII activity and facilitated INa,L was confirmed in both healthy and diseased myocardium by others [157,176,177].…”