Interaction of arginine vasopressin and angiotensin II on Ca2+ in vascular smooth muscle cells

Interaction of arginine vasopressin and angiotensin II on Ca 2+ in vascular smooth muscle cells. The non-osmotic release of arginine vasopressin (AVP) is associated with the concomitant activation of the renin-angiotensin and sympathetic nervous systems. In vivo studies suggest that a positive interaction may occur between AVP and angiotensin II (Ang II), and other Ca 2+ mobilizing hormones. In the present study, the cellular mechanisms of this interaction between AVP and Ang II in vascular smooth muscle cell (VSMC) were examined. These results support the existence of a positive interaction between AVP and Ang II on Ca 2+ mobilization in VSMC. In fact, the challenge of VSMC with combined AVP and Ang II, in a range from 5 × 10 -11 to 10 -8 M, enhanced cytosolic free Ca 2+ ([Ca 2+ ] i ) and 45 Ca 2+ efflux in a more than additive manner. This potentiation, which was not dependent of the presence of extracellular calcium, correlated with an increased VSMC shape change. Moreover, the combination of subthreshold doses of AVP and Ang II (5 × 10 -11 M), which do not release Ca 2+ alone, evoked a Ca 2+ mobilizing response. A subthreshold dose of Ang II also shifted to the left the concentration-response curve of the AVP-mediated 45 Ca 2+ efflux. Since there were no changes in receptor binding of either hormone by the other hormone and the interaction of the two hormones on the production of inositol phosphatides was additive, the AVP and All positive interaction on Ca 2+ mobilization on VSMC may occur at the level of the intracellular Ca 2+ -releasing mechanism itself. Such an interaction can occur at hormone concentrations below the Ca 2+ release threshold and may explain an increased functional response to the combination of pressor hormones compared to that of each hormone alone.