EFFECTS OF INORGANIC ANIONS ON THE CONTRACTILITY OF VASCULAR SMOOTH MUSCLE

Abstract

Contractile responses of isolated loops of rabbit aorta tissues were first recorded in normal Krebs solution and subsequently in a modified Krebs medium in which chloride ions were substituted with equivalent amounts of one of the foreign anions, Br − , NO 3 − , I − , SCN − , or SO 4 2− . With potassium sulfate or noradrenaline as the stimulating agent, responses of the tissues exposed to these anions for 1 minute and for 16 minutes were recorded. Potassium-induced contractions were potentiated in the presence of Br − , NO 3 − , I − , and SCN − ions but were depressed in the presence of SO 4 2− ions. Responses to noradrenaline after 1-minute exposures were depressed in the presence of all the foreign anions whereas those induced after 16-minute exposures were potentiated by Br − and NO 2 − ions but were still depressed by I − , SCN − , and SO 4 2− ions. The alterations in contractility produced by foreign anions have been attributed to their influence on the binding, release, and rebinding of calcium ions. The differences between responses induced by K 2 SO 4 and noradrenaline in the presence of foreign anions can be related to the utilization of calcium from different binding sites in the cell membrane.