NA,K-ATPASE IN EXCITATION-CONTRACTION COUPLING OF VASCULAR SMOOTH-MUSCLE FROM CATTLE

Abstract

Lowering the extracellular K+ content from 6 to 0.6 mM causes a rise, and elevation from 6 to 8.5 mM a fall of 45Ca2+ efflux from the vascular smooth muscle cells of the arteria carotis communis of cattle. A level of 17 mM K+ has no influence. Removal of extracellular Ca does not block these effects. Ouabain (10-4 M) also induces a rise in Ca2+ efflux, additional K reduction then being without effect; 10-9 M ouabain is of no influence. The 45Ca2+ efflux kinetics correlates with the activity of the isolated Na, K-ATPase. Tonus increases of the vascular strips by 10-4 M ouabain and K deficiency cannot be blocked by 4 mM La or removal of extracellular Ca. Unlike Na, K stimulates the active Ca2+ binding and the activity of the Ca-ATPase of the microsomal fraction. The active Ca2+ binding of the mitochondria is stimulated by both ions. The plasma membrane Na, K-pump can regulate the tonus of big arteries through alteration of Ca2+ storage processes.