Role of protein kinase Cα and mitogen-activated protein kinases in endothelin-1-stimulation of cytosolic phospholipase A2 in iris sphincter smooth muscle

We have investigated the roles of protein kinase C (PKC) and mitogen-activated protein kinases (MAPK) in the phosphorylation and activation of cytosolic phospholipase A(2) (cPLA(2)) in endothelin-1- (ET-1) stimulated cat iris sphincter smooth muscle (CISM) cells. We found that in these cells both PKC and p38 MAP kinases play a critical role in ET-1-induced cPLA2 phosphorylation and arachidonic acid (AA) release. Our findings indicate that stimulation of the endothelin-A- (ETA) receptor leads to: (1) activation of Gq protein which stimulates phospholipase C to hydrolyze the polyphosphoinositide PIP2 into diacylglycerol (DAG) and inositol trisphosphate (IP3) the DAG may then activate PKC to phosphorylate and activate cPLA(2); and (2) activation of Gi protein, which, through a series of kinases, leads to the stimulation of p38 MAPK and subsequently to phosphorylation and activation of cPLA(2). The ability of the activated ETA-receptor, which is coupled to both Gq and Gi proteins, to recruit and activate this complex signal transduction mechanism remains to he clarified.