Intracellular messenger for action of angiotensin II on fluid transport in rabbit proximal tubule.

These studies were designed to examine the cellular messenger that mediates the action of angiotensin II on fluid transport (Jv) in the rabbit proximal tubule. We measured the effects of angiotensin II on Jv, activation of adenylate cyclase, and the concentration of cytosolic free calcium (Cai) in the rabbit proximal tubule. In nine rabbit proximal convoluted tubules (PCT), angiotensin II, 10(-8) M and 10(-6) M, decreased Jv by 18 and 25%, P less than 0.05. In eleven rabbit proximal straight tubules (PST), 10(-8) and 10(-6) M angiotensin II decreased Jv by 20 and 23%, P less than 0.02. Angiotensin II did not affect lumen-to-bath phosphate fluxes in PCT or PST, and it did not activate adenylate cyclase in PST. In a preparation of proximal tubules (PCT and PST) loaded with aequorin, angiotensin II, 10(-8) and 10(-6) M, transiently increased Cai by 13 and 32%, P less than 0.001. We propose that Cai surges, activated by angiotensin II, are part of a cellular message that inhibits Jv in the rabbit proximal tubule.