Calcium Efflux in Rat Tail Artery during Potassium Induced Relaxation

The current study investigates the mechanism by which the concentration of activator Ca²⁺ is decreased during potassium induced relaxation of vascular smooth muscle. 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 potassium after contraction induced by norepinephrine in potassium-free solution. The efflux of ⁴⁵Ca²⁺ from the strips was stimulated by norepinephrine during the potassium-free cycle. This increase in efflux was prevented during potassium induced relaxation. D-600, an inhibitor of transmembrane Ca²⁺ flux, reduced the magnitude of potassium induced relaxation by 35%. These observations suggest that relaxation in response to potassium is the result of a decrease in membrane permeability to Ca²⁺ coupled with an increase in Ca²⁺ sequestration at intracellular sites.