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

Abstract

An increase in intracellular Ca2+ concentration ([Ca2+]i) augments late sodium current ( INa.L) in cardiomyocytes. This study tests the hypothesis that both Ca2+-calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) mediate the effect of increased [Ca2+]i to increase INa.L. Whole cell and open cell-attached patch clamp techniques were used to record INa.L in rabbit ventricular myocytes dialyzed with solutions containing various concentrations of [Ca2+]i. Dialysis of cells with [Ca2+]i from 0.1 to 0.3, 0.6, and 1.0 μM increased INa.L in a concentration-dependent manner from 0.221 ± 0.038 to 0.554 ± 0.045 pA/pF ( n = 10, P < 0.01) and was associated with an increase in mean Na+ channel open probability and prolongation of channel mean open-time ( n = 7, P < 0.01). In the presence of 0.6 μM [Ca2+]i, KN-93 (10 μM) and bisindolylmaleimide (BIM, 2 μM) decreased INa.L by 45.2 and 54.8%, respectively. The effects of KN-93 and autocamtide-2-related inhibitory peptide II (2 μM) were not different. A combination of KN-93 and BIM completely reversed the increase in INa.L as well as the Ca2+-induced changes in Na+ channel mean open probability and mean open-time induced by 0.6 μM [Ca2+]i. Phorbol myristoyl acetate increased INa.L in myocytes dialyzed with 0.1 μM [Ca2+]i; the effect was abolished by Gö-6976. In summary, both CaMKII and PKC are involved in [Ca2+]i-mediated augmentation of INa.L in ventricular myocytes. Inhibition of CaMKII and/or PKC pathways may be a therapeutic target to reduce myocardial dysfunction and cardiac arrhythmias caused by calcium overload.