Analysis of angiotensin‐stimulated sodium transport in cultured smooth muscle cells from rat aorta

Angiotensin peptides (AI, AII, AIII) increased the rate of Na + accumulation by smooth muscle cells (SMC) cultured from rat aorta. The stimulatory effect of All on Na + uptake was observed which Na + exodus via the Na + /K + pump was blocked either by ouabain or by the removal of extracellular K + . All was at least ten times more potent than AIII and about 100 times more potent than AI in stimulating Na + uptake. Saralasin had little effect on Na + uptake by itself but almost completely blocked the increase caused by All. The stimulation of net Na + entry by AI, but not AII, was prevented by protease inhibitors. The stimulation of Na + uptake was almost completely blocked by amiloride. Tetrodotoxin, which prevented veratridine from increasing Na + uptake, had no effect on the response to AII. Angiotensin increased the rate of ouabain‐sensitive 86 Rb + uptake (Na + /K + pump activity) but had no effect on ouabain‐sensitive ATPase activity in frozen‐thawed SMC or in microsomal membranes isolated from cultured SMC. The stimulation of ouabain‐sensitive 86 Rb + uptake by All was blocked by saralasin. Omitting Na + from the external medium prevented All from increasing 86 Rb + uptake. All had no effect on cell volume or cyclic AMP levels in the cultured SMC. These results suggest that angiotensin peptides activate an amiloride‐sensitive Na + transporter which supplies the Na + /K + pump with more Na + , its rate‐limiting substrate.