Species Differences in the Inhibitory Effect of Ouabain on High K-Induced Contraction in the Ileal Longitudinal Muscle

Abstract

Effects of ouabain on a high K-induced contraction and intracellular Na and K contents of the ileal longitudinal muscle preparations isolated from various animal species was compared. In muscles of various animals (monkey, dog, cat, rabbit, guinea-pig, rat and mouse), the high K-induced contraction was inhibited by verapamil (5 X 10(-8) M) or ouabain (3 X 10(-6) M), and both the inhibitions were antagonized by an increase in external Ca in a competitive manner. Species differences were shown in the ouabain effect but not in the verapamil one. Regarding the sensitivity to ouabain, the muscles were divided into two groups, that is, the muscle from monkey, rabbit, guinea-pig or dog belongs to the high sensitivity group, and that from cat, rat or mouse belongs to the low one. The order of sensitivities of the muscles to ouabain in the relaxation was consistent with that in Na,K-ATPase inhibition, as reported by Repke et al. (1965). Intracellular Na contents of muscles were increased by an addition of ouabain to the high K solution, and the rate and amount of the accumulation of intracellular Na varied in these muscles. Except for the cat muscle, a high correlation was noted between the ouabain-induced relaxation and the amount of intracellular Na accumulation. However, the regression coefficients were variable: 4.1 in the monkey muscle, 2.2 in the rat one, and about 1.0 in the others. That is, the monkey muscle showing the high regression coefficient value probably has a high sensitivity to the inhibition of intracellular Na in the high K-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)