Stimulation of phospholipase C-mediated hydrolysis of phosphoinositides by endothelin in cultured rabbit aortic smooth muscle cells

Abstract

Incubation of the [ 3H]inositol-labeled cultured rabbit vascular smooth muscle cells (VSMCs) with either endothelin or angiotensin II caused a rapid formation of inositol mono-, bis- and trisphosphates (IP 1, IP 2 and IP 3, respectively). Time courses of the endothelin- and angiotensin II-induced formation of these inositol phosphates were similar. The maximal levels of IP 1, IP 2 and IP 3 formation induced by endothelin were about 50%, 25% and 40%, respectively, of those induced by angiotensin II. The doses of endothelin necessary for the half maximal and maximal extents of the formation of IP 1 were about 1 nM and 100 nM, respectively. Protein kinase C-activating 12- O -tetradecanoylphorbol-13-acetate (TPA) inhibited the endothelin-induced formation of IP 1 with the half maximal extent of inhibition seen at 3 nM. The inhibitory action of TPA was mimicked by another protein kinase C-activating phorbol ester, phorbol-12,13-dibutyrate, but not by 4α-phorbol-12,13-didecanoate, known to be inactive for this enzyme. These results indicate that endothelin causes the phospholipase C-mediated hydrolysis of phosphoinositides, though to a lesser extent than angiotensin II, in cultured VSMCs and suggest that protein kinase C modulates the signaling mechanism of endothelin to the phospholipase C.