VASOPRESSIN INDUCES ARACHIDONIC-ACID RELEASE THROUGH PERTUSSIS-TOXIN-SENSITIVE GTP-BINDING PROTEIN IN AORTIC SMOOTH-MUSCLE CELLS - INDEPENDENCE FROM PHOSPHOINOSITIDE HYDROLYSIS

We previously reported that pertussis toxin (PTX) had little effect on arginine vasopressin-induced formation of inositol trisphosphate (IP3 ) in rat aortic smooth muscle cells [Kondo et al.: Biochemical and Bio physical Research Communications 161:677-682, 1989]. In the present st udy, we investigated the mechanism of vasopressin-induced arachidonic acid release in rat aortic smooth muscle cells. Vasopressin stimulated both the release of arachidonic acid and the formation of IP3 dose de pendently in the range between 10 pM and 1 muM. The effect of vasopres sin on arachidonic acid release was more potent than that on the forma tion of IP3. Quinacrine, a phospholipase A2 inhibitor, significantly s uppressed the vasopressin-induced arachidonic acid release but had lit tle effect on the formation of inositol phosphates. NaF, a GTP-binding protein activator, mimicked vasopressin by stimulating the arachidoni c acid release. The arachidonic acid release stimulated by a combinati on of vasopressin and NaF was not additive. PTX partially but signific antly suppressed the vasopressin-induced arachidonic acid release. In the cell membranes, PTX catalyzed ADP-ribosylation of a protein with a n Mr of about 40,000. Pretreatment of membranes with 0.1 muM vasopress in in the presence of 2.5 mM MgCl2 and 100 muM GTP markedly attenuated this PTX-catalyzed ADP-ribosylation of the protein in a time-dependen t manner. These results strongly suggest that PTX-sensitive GTP-bindin g protein is involved in the coupling of vasopressin receptor to phosp holipase A2 in primary cultured rat aortic smooth muscle cells. (C) 19 93 Wiley-Liss, Inc.