Calcium Efflux in Rat Tail Artery during Potassium Induced Relaxation

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Abstract
The mechanism by which the concentration of activator Ca2+ is decreased during K induced relaxation of vascular smooth muscle is investigated. Helically cut strips of rat tail artery were mounted between a fixed base and force transducers; isometric contractions were recorded. The arterial strips relaxed in response to K after contraction induced by norepinephrine in K-free solution. The efflux of 45Ca2+ from the strips was stimulated by norepinephrine during the K-free cycle. This increase in efflux was prevented during K induced relaxation. D-600 [.alpha.-isopropyl-.alpha. [(N-methyl-N-homoveratryl)-.gamma.-aminopropyl]-3,4,5-trimethoxyphenyllacetonitrile], an inhibitor of transmembrane Ca2+ flux, reduced the magnitude of K induced relaxation by 35%. Relaxation in response to K is due to a decrease in membrane permeability to Ca2+ coupled with an increase in Ca2+ sequestration at intracellular sites.