Adenylyl cyclase isoforms and signal integration in models of vascular smooth muscle cells

Adenylyl cyclases present a potential focal point for signal integration in vascular smooth muscle cells (VSMC) influencing contractile state and cell ular responses to vessel wall injury. In the present study, we examined the influence of the vasoactive peptide arginine vasopressin (AVP) on cAMP reg ulation in primary cultures of rat aortic VSMC and in the A7r5 arterial smo oth muscle cell line. In cultured VSMC and A7r5 cells, AVP had no effect on basal cAMP but differentially affected beta -adrenergic receptor-induced a ctivation of adenylyl cyclase. AVP synergistically increased (twofold) isop roterenol-stimulated cAMP production in VSMC but inhibited the effect of is oproterenol (50%) in the A7r5 cell line. The effects of AVP in both prepara tions were blocked when cells were pretreated with a selective V-1 vasopres sin receptor antagonist. Moreover, the actions of AVP in both models were d ependent on release of intracellular Call and were mimicked by elevation of Ca2+ with the ionophore A23187, suggesting that the responses to AVP invol ve Ca2+-mediated regulation of adenylyl cyclase stimulation. Adenylyl cycla se types I, III, and VIII are stimulated by Ca2+/calmodulin, whereas types V and VI are directly inhibited by Ca2+. RNA blot analysis for effector iso types indicated that both VSMC and A7r5 cells expressed types III, V, and V I. VSMC also expressed mRNA for type IV and VIII effectors, which could acc ount for the cell-specific responses to peptide hormone and Ca2+.