MODULATION OF NA-KINASE-C IN CARDIAC-CELLS( CURRENT INACTIVATION BY STIMULATION OF PROTEIN)

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 ra t ventricular myocytes using whole-cell patch-clamp techniques. Perfus ion with 2 nmol/L PKCP caused a depolarizing shift in steady state hal f-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 inacti vation was slowed by PKCP (tau, 69.1 +/- 7.6 [control] versus 100.4 +/ - 5.1 ms). Open-channel inactivation, estimated by measuring I-Na deca y from peak current at test voltages between -10 and +30 mV was signif icantly slowed by PKCP. Recovery from inactivation was more rapid duri ng PKCP perfusion, with a shortening of both the fast (tau(f)) and slo w (tau(s)) components of tau (tau(f), 38.5 +/- 7.0 [control] versus 14 .2 +/- 4.7 ms; tau(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 inhi bitors chelerythrine chloride or staurosporine or by downregulation of PKC using phorbol ester preincubation. We conclude that the actions o f PKC on the Na+ channel result in slowing the development of inactiva tion and accelerating reactivation, resulting in less resting inactiva tion.