The possibility of a role of the sarcolemmal Na-K pump of arterial smooth muscle in the mechanism of action of adenosine was explored in this study. Isolated helical strips of rabbit coronary and femoral arteries were suspended in organ baths with physiological salt solution, and isometric contractions were recorded. Concentration-dependent relaxations produced by adenosine were attenuated during Na-K pump inhibition. Ouabain (1 X 10(-5) M) significantly increased the adenosine ED50 values from 9.6 X 10(-8) M to 2.9 X 10(-7) M and from 9.4 X 10(-7) M to 8.4 X 10(-6) M in coronary and femoral artery strips, respectively. Similar results were obtained by substitution of LiCl for NaCl in the bathing solution and with a K-free solution. These effects were not attributable to augmented initial active tension, time-dependent changes in adenosine response or the release of norepinephrine from adrenergic nerve terminals. In addition, adenosine enhanced potassium-induced relaxation, an index of Na-K pump activity in isolated vascular strips. The data suggest that sarcolemmal Na-K pump activity may contribute directly or indirectly to the mechanism of action of adenosine.