Angiotensin II Potentiates Vasopressin-Dependent cAMP Accumulation in CHO Transfected Cells. Mechanisms of Cross-Talk Between AT 1A and V 2 Receptors

Abstract

The V 2 vasopressin and the AT 1A angiotensin II receptors are respectively coupled to the adenylyl cyclase and the phosphoinositide pathways. The cross-talk between these two receptors and their transduction pathways were investigated in CHO cells transfected with cDNA of both AT 1A and V 2 receptors. In these cells, angiotensin II induced an increase in intracellular calcium, and vasopressin a rise in intracellular cAMP accumulation. The simultaneous addition of angiotensin II and vasopressin potentiated the production of cAMP by the V 2 receptor. This potentiation was dose-dependent and, at a concentration of 10 −7M angiotensin II, the accumulation of cAMP was 4-fold greater than that induced by 10 −7M vasopressin alone. Such cross-talk occurred in the presence and absence of cyclic nucleotide phosphodiesterase inhibitors, indicating that inhibition of phosphodiesterase activity was not the principal cause of potentiation. This was confirmed by the absence of calcium-inhibitable isoforms of phosphodiesterases in CHO cells. The addition of angiotensin II to forskolin, which stimulates the adenylyl cyclase, did not modify the production of cAMP. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), partially mimicked, and staurosporine, an inhibitor of PKC, partially inhibited the effect of angiotensin II on vasopressin. Chelation of intracellular calcium with BAPTA-AM markedly reduced the potentiation of V 2 receptor by angiotensin II. However, increase in intracellular calcium with thapsigargin did not modify the cAMP accumulation induced by vasopressin. It was concluded that, in CHO cells, activation of the AT 1A receptor by angiotensin II potentiates the V 2 receptor through activation of protein kinase C in the presence of intracellular calcium at a step located between the receptor and the adenylyl cyclase.