VASOPRESSIN-INDUCED ACTIVATION OF PROTEIN-KINASE-C IN RENAL EPITHELIAL-CELLS

Recent studies indicate that the actions of arginine vasopressin (AVP) and other agonists that stimulate electrogenic sodium transport in re nal epithelial A6 cells are linked to a Ca2+-mobilizing signal transdu ction mechanism that involves generation of inositol trisphosphate. Si nce diacylglycerol is the other product in this pathway, studies were performed to determine the possible rule of PKC in the stimulation of sodium transport. AVP induced a biphasic increase in diacylglycerol ge neration, characterized by an initial rapid rise and then a sustained elevation, and PKC activation, reflected by phosphorylation of a speci fic 80 kDa myristoylated alanine-rich PKC substrate (MARCKS). To deter mine the PKC isoform(s) involved in this process, immunoblot analysis was performed using antisera that recognize both classical PKC isoform s, XPKC-I and XPCK-II, cloned from Xenopus oocytes. The transcripts of both isoforms were expressed in the A6 cell. Since protein recognized by antisera was translocated from cytosol to the I?articulate fractio n after exposure to AVP, one or both isoforms were activated in the A6 cell. Further studies showed that cyclohexyladenosine and insulin, ad ditional agonists of sodium transport in A6 cells, also stimulated pho sphorylation of MARCKS, These results argue that Ca2+-dependent PKC is involved in the action of AVP, and that of other agonists, which stim ulate sodium transport. (C) 1998 Elsevier Science B.V.