Phorbol ester inhibits arginine vasopressin activation of phospholipase C and promotes contraction of, and prostaglandin production by, cultured mesangial cells

We have previously shown that arginine vasopressin (AVP) causes a rapid (5-10 min) contractile response in cultured mesangial cells plated onto slippery substrata such as poly(hydroxyethyl methacrylate)-coated dishes. This contraction is associated with an increase in the levels of inositol trisphosphate (InsP₃), diacylglycerol and prostaglandin E₂ (PGE₂). We now report that agents which are known to activate protein kinase C, i.e. phorbol 12-myristate 13-acetate (PMA) and oleolylacetylglycerol (OAG), also contract mesangial cells; however, the contractile response is slow to develop (15-30 min). The inactive phorbol ester, 4α-phorbol 12,13-didecanoate, did not elicit contraction. PMA and OAG did not increase InsP₃ release in mesangial cells. However, pretreatment of mesangial cells with PMA inhibited the formation of InsP₃. This inhibition could not be explained by a reduction in AVP binding since PMA treatment did not influence the number of affinity or [³H]AVP binding sites in intact cells. PMA alone stimulated PGE₂ production in mesangial cells to a degree similar to AVP. Contrary to what seen with InsP₃, pretreatment of cells with PMA before AVP had an additive effect on arachidonic acid release and PGE₂ production. Thus, there is an apparent dissociation of phospholipase C activity from that of phospholipase A₂.