Effects of Strontium as Substitute for Extracellular Calcium on Contraction and Relaxation of Vascular Smooth Muscle

Abstract

Contraction of a muscle is activated by a rise in intracellular free-Ca²⁺ concentration (1). It was shown that there are different trigger mechanisms that activate the contractile apparatus of vascular smooth muscle by causing an increase in the intracellular Ca²⁺ concentration (2). The source of Ca²⁺ may be extracellular, intracellular, or both, depending on the type of trigger mechanisms (2,3). At present, the source of the activator Ca²⁺ of individual trigger mechanisms remains the subject of study. In contraction of various types of muscles, it is known that Sr²⁺ is effective as a substitute for external Ca²⁺ (4–7). The purpose of this report is to determine whether Sr²⁺ can substitute for external Ca²⁺ in inducing contraction and relaxation and to compare the effectiveness between Ca²⁺ and Sr²⁺ in several types of contraction and relaxation of vascular smooth muscle. The following different types of contraction were selected as representative samples to be studied: (1) spontaneous rhythmic contraction of rat portal vein, (2) spontaneous tonic contraction of rat skeletal muscle artery, (3) potassium-induced contraction of dog external jugular vein and dog mesenteric artery, and (4) norepinephrine-induced contraction of dog external jugular vein and dog mesentric artery.