Vasopressin stimulates tyrosine phosphorylation by activation of PKC in the rat smooth muscle cell line, A-10.

Arginine vasopressin (AVP)-induced tyrosine phosphorylation was studied in a rat smooth muscle cell line, A-10, by western blotting, using a monoclonal antibody against phosphotyrosine. AVP stimulated the phosphorylation of several cellular proteins of molecular mass 60-130 kDa in a time- and dose-dependent manner. Phosphorylation was mediated largely by V(1)receptor subtype since it was inhibited by selective V(1)antagonist and was only partially elicited by the V(2)agonist, desmopressin. Heterotrimeric G-proteins seemed to be involved in the phosphorylation mechanism because fluoraluminates, an activator of heterotrimeric G-proteins (and thus an uncoupler of the receptor-G-protein interaction) inhibited the AVP-induced phosphorylation. The protein kinase C (PKC) inhibitors: staurosporine, H7 and GF109203X are able to block the AVP-stimulated phosphorylation. The last of these has been shown to be one of the most selective inhibitors of PKC. These results indicate that PKC is upstream of the phosphorylation, a motion which is supported by the fact that the AVP-stimulated phosphorylation was downregulated by phorbol esters.