Tyrosine kinase signaling pathways modulate angiotensin II-induced calcium ([Ca2+](i)) transients in vascular smooth muscle cells

Tyrosine kinases have been implicated in vascular smooth muscle cell proliferation and contraction. Underlying mechanisms may involve Ca2+-dependent pathways. This study assesses relationships between angiotensin II (Ang II)-stimulated phospholipase C-mediated Ca2+ transients and tyrosine kinase-dependent pathways in vascular smooth muscle cells. Intracellular free Ca2+ concentration ([Ca2+](i)) was measured in primary cultured unpassaged vascular smooth muscle cells derived from mesenteric resistance vessels of Wistar-Kyoto rats with the use of fura 2 methodology. [Ca2+](i) effects of Ang II (1 nmol/L) were determined in vascular smooth muscle cells in which tyrosine kinase pathways were stimulated by insulin (70 mu U/mL; 0.5 nmol/L), insulin-like growth factor-I (1 ng/mL; 0.13 nmol/L), or platelet-derived growth factor-BB (1 ng/mL; 0.04 nmol/L) and in cells in which tyrosine kinase was inhibited by specific inhibitors (1 mu mol/L tyrphostin A-23 and genistein). Ang II elicited a rapid and transient [Ca2+](i) response (from 94+/-8 to 239+/-5.8 nmol/L). Activation of the receptor tyrosine kinase by insulin, platelet-derived growth factor, and insulinlike growth factor-I significantly reduced (P<.01) Ang II-induced [Ca2+](i) to 161+/-7, 189+/-3.7, and 183+/-5 nmol/L, respectively. In the presence of tyrphostin A-23 and genistein, Ang II-stimulated [Ca2+](i) remained persistently elevated and failed to return to basal levels. Tyrphostin A 1; the inactive tyrphostin analogue, had no significant effect on Ang II-induced [Ca2+](i). This study demonstrates that activation of tyrosine kinase pathways reduces Ang II-elicited [Ca2+](i) responses, whereas tyrosine kinase inhibition prevents [Ca2+](i) recovery after agonist stimulation. Interaction between tyrosine kinase- and phospholipase C-dependent signaling pathways modulates vascular smooth muscle cell [Ca2+](i) responses to Ang II.