Inhibition of potassium-induced contracture of the isolated rat aorta by amiloride

Potassium contractures of helically cut strips of rat aorta were recorded isometrically. Contractures induced by KCl 40 mmol/l were decreased dose-dependently by amiloride (1.7 X 10(-5) to 1.4 X 10(-4) mol/l) added to the bath 10 min before the depolarization. Ouabain (10(-3) mol/l) antagonized this effect. Contractures induced by using, instead of normal Krebs solution, a solution in which potassium was replaced by sodium (Krebs potassium) were also decreased dose-dependently by amiloride, but the slope of the linear log dose-effect curve line was steeper. When arteries were incubated in a solution deprived of sodium and calcium (isotonicity maintained by choline), the intensity of consecutive contractures by Krebs potassium decreased progressively. Incubation in a normal Krebs solution restored the normal contractures; amiloride added at the same time prevented this restoration. These findings are in agreement with the assumption that sodium-calcium exchange plays an important part in the contracture of vascular smooth muscles.