ROLE OF INTRACELLULAR CALCIUM IN THE ANGIOTENSIN II-MEDIATED TYROSINEPHOSPHORYLATION AND DEPHOSPHORYLATION OF PLC-GAMMA-1

Angiotensin II induces the rapid temporal tyrosine phosphorylation and activation of phospholipase C-gamma 1 (PLC-gamma 1) and the elevation of intracellular calcium levels. To investigate the relationship of t hese intracellular signaling events, rat aortic smooth muscle cells we re treated with the calcium chelator BAPTA-AM, the calcium channel blo cker verapamil, the intracellular calcium antagonist TMB-8, and the ca lcium ionophore ionomycin. The effects of these agents on PLC-gamma 1 tyrosine phosphorylation were then measured. We found that treatment o f these cells with the calcium inhibitors augmented the basal level of PLC-gamma 1 tyrosine phosphorylation, without changing the peak level of tyrosine phosphorylation induced by angiotensin II. The rapid deph osphorylation of PLC-gamma 1 that follows angiotensin II stimulation w as prevented by these calcium antagonists. In contrast, angiotensin II -induced tyrosine phosphorylation of PLC-gamma 1 was inhibited by iono mycin. These results suggest that the angiotensin II-induced tyrosine phosphorylation of PLC-gamma 1 is calcium-independent, while the depho sphorylation is calcium-dependent. (C) 1997 Academic Press.