Modulation of Na + Current Inactivation by Stimulation of Protein Kinase C in Cardiac Cells

Abstract

Abstract Modulation of the inward Na + current ( I Na ) by protein kinase C (PKC) was investigated by intracellular perfusion of a peptide corresponding to the catalytic subunit of PKC (PKCP). The effects of PKC activation independent of membrane-receptor pathways were studied in neonatal rat ventricular myocytes using whole-cell patch-clamp techniques. Perfusion with 2 nmol/L PKCP caused a depolarizing shift in steady state half-inactivation relative to control (−83.2±1.3 versus −74.9±1.6 mV for control versus PKCP, respectively) without a change in current-voltage relationships or peak I Na . The development of resting inactivation was slowed by PKCP (τ, 69.1±7.6 [control] versus 100.4±5.1 ms). Open-channel inactivation, estimated by measuring I Na decay from peak current at test voltages between −10 and +30 mV was significantly slowed by PKCP. Recovery from inactivation was more rapid during PKCP perfusion, with a shortening of both the fast (τ f ) and slow (τ s ) components of τ (τ f , 38.5±7.0 [control] versus 14.2±4.7 ms; τ s , 163.4±47.9 [control] versus 51.3±9.2 ms). All of the effects of PKCP on I Na were antagonized by the PKC inhibitors chelerythrine chloride or staurosporine or by downregulation of PKC using phorbol ester preincubation. We conclude that the actions of PKC on the Na + channel result in slowing the development of inactivation and accelerating reactivation, resulting in less resting inactivation.