LYSOPHOSPHATIDYLCHOLINE MODULATES CARDIAC I-NA VIA MULTIPLE PROTEIN-KINASE PATHWAYS

Lysophosphatidylcholine (LPC) is a naturally occurring intracellular p hospholipid metabolite that has been implicated in arrhythmogenesis du ring ischemia. LPC has been shown to affect the cardiac Na+ current (I -Na), but the mechanism of modulation remains undescribed. Recently, l ow concentrations of LPC have been shown to activate protein kinase C (PKC) independent of the receptor-delineated pathway. The purposes of this study were to describe the effects of intracellularly introduced LPC on I-Na and to determine if these effects were mediated by kinases . Modulation of I-Na was studied in ventricular cells with LPC (1 nmol /L to 1 mu mol/L) internally applied using whole-cell patch-clamp tech niques. Intracellular LPC caused a dose-dependent depolarizing shift o f steady state inactivation that was accompanied by a change in slope factor. The development of resting inactivation from closed states was delayed 40%, whereas the recovery from inactivation was significantly accelerated. These results were mimicked by another bioactive lipid, lysophosphatidylethanolamine, or by a peptide analogue of PKC, which i s a potent stimulator of endogenous PKC activity. Maximal recruitable current was significantly increased by LPC but not by PKC activation. Some of the effects of LPC on I-Na could be partially inhibited by the specific PKC inhibitor chelerythrine chloride or by downregulation of PKC with phorbol ester pretreatment. However, genistein, a specific t yrosine kinase inhibitor, completely inhibited all the modulation of I -Na caused by LPC. These data suggest that LPC modulates I(Na)caused b y LPC. These data suggest that LPC modulates I-Na in cardiac myocytes by a pathway that involves both PKC-dependent and tyrosine kinase-depe ndent phosphorylation.