Influence of Magnesium on Calcium- and Potassium-Related Responses in Vascular Smooth Muscle

Abstract

The influence of Mg on Ca- and K-related responses of rabbit aortic strips was studied. Aortic strips bathed in either a K-free or 60.0 mM K solution were less sensitive to Ca in the presence of 1.2 mM Mg. Ca induced greater maximum tension in the aortic strips in the presence of Mg when bathed in 60.0 mM K. Addition of K to a K-free medium induced a slight relaxation at low concentrations (45Ca uptake was stimulated at all K concentrations producing a contraction. Mg depressed this increase in uptake. ⁴⁵Ca efflux was more rapid into a 50.0 mM than into 0.0 mM K solution. Mg delayed ⁴⁵Ca efflux. It is concluded from these data that Mg has two components in its effect on the Ca associated with K responses. One is a competition with Ca at extracellular sites probably at the membrane, and the other is intracellular, probably a competition with Ca at sequestration sites.