PHOSPHOLIPASE-C ACTIVATES PROTEIN-KINASE-C DURING INDUCTION OF SLOW NA CURRENT IN XENOPUS OOCYTES

Protein phosphorylation by protein kinase C (PKC) has recently been sh own to be a key event in the induction of the slow inward Na current o bserved during sustained depolarization of the Xenopus oocyte membrane . The present work investigates the possible pathways leading to PKC a ctivation. PKC is activated by a series of phospholipid metabolites, s uch as diacylglycerol (DAG) and arachidonic acid produced by phospholi pases C (PLC) and A(2) (PLA(2)) respectively. To test whether PKC acti vation was dependent upon the phospholipid metabolites produced either by PLC or by PLA(2), enzyme activity was reduced using selective inhi bitors. Results indicated that inhibition of PLA(2) activity and inhib ition of the enzymes involved in the arachidonic acid cascade failed t o affect Na current amplitude. On the other hand, PLC inhibition cause d a marked decrease of Na current amplitude. In another series of expe riments, Na current was fully restored, in spite of PLC inhibition, by directly enhancing PKC activity with a powerful activator phorbol 12- myristate 13-acetate. These data strongly suggest that PLC is involved in PKC activation during Na channel induction.