POTASSIUM RELAXATION OF VASCULAR SMOOTH-MUSCLE FROM SPONTANEOUSLY HYPERTENSIVE RATS

Abstract

Helical strips of tail artery from spontaneously hypertensive (SHR) and Kyoto Wistar normotensive rats (WKY) relaxed in response to K after contraction induced by norepinephrine in K-free solution. Helical strips from SHR consistently showed greater relaxation in response to the addition of K than those from WKY. The amplitude of K-induced relexation is an index of the activity of electrogenic Na-K transport and Na-K ATPase. The Na-K ATPase activity of SHR vascular smooth muscle is increased as compared to WKY. Ouabain eliminated K-induced relaxation in both SHR and WKY strips. K-induced relaxation in SHR was more sensitive to ouabain inhibition than in WKY. Relaxation induced by K in SHR and WKY strips varied with the length of incubation in K-free solution and the concentration of K added back. Apparently SHR have an increased intrinsic Na-K ATPase activity or an enzyme activity stimulated more by an elevated intracellular Na concentration due to incubation in K-free solution.