Ouabain binding and potassium relaxation in aortas from renal hypertensive rabbits

This study was designed to characterize the electrogenic sodium pump in vascular smooth muscle from one-kidney one-clip (1K-1C), renal hypertensive rabbits. Two measures of the electrogenic pump were used: 1) [3H]ouabain binding and 2) potassium-induced relaxation. The binding study indicated a significant increase in the affinity of pump sites for ouabain in aortic strips from hypertensive rabbits compared with those from normotensive rabbits (Scatchard analysis). The maximal binding capacity of the binding sites was similar in the two groups of animals, whereas the concentration of ouabain at which half-maximal binding occurred was lower in the aortic strips from hypertensive rabbits. Aortic strips from hypertensive rabbits showed greater sensitivity to the relaxant effect of potassium after incubation in potassium-free solution. The potassium-induced relaxation in aortic strips from hypertensive rabbits was more sensitive to the inhibitory effect of ouabain than that in strips from normotensive rabbits. These results suggest that the increased sensitivity to potassium and ouabain in vascular smooth muscle from hypertensive rabbits is due to an increased affinity of the pump sites for these substances.