Diminished arterial smooth muscle response to sodium nitroprusside during Na-K pump inhibition.

Helical strips of rabbit coronary and femoral arteries were used to determine whether Na-K pump inhibition would diminish relaxation in response to sodium nitroprusside. Ouabain (10(-5) M) decreased relaxation by 10(-7) M sodium nitroprusside from 87.0 +/- 5.4 to 65.2 +/- 9.1% in coronary, and from 62.0 +/- 6.9 to 32.8 +/- 3.3% in femoral artery strips. A low Na solution and a K-free solution also decreased relaxation by sodium nitroprusside. Relaxation in response to K+, an index of Na-K pump activity in arterial smooth muscle, was enhanced in the presence of sodium nitroprusside. These results may reflect an interaction between sodium nitroprusside and the sarcolemmal Na-K pump of arterial smooth muscle.