Inhibition of the Vasodilator Effect of Hypercapnic Acidosis by Hypercalcemia in Dogs and Rats

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Abstract
The vasodilator effect of local hypercapnic acidosis, produced by intra-arterial infusion of an acid buffer solution consisting of a mixture of glycine and hydrochloric acid, in the perfused hind limb and in the perfused gastrocnemius muscle of anesthetized dogs was examined at normal plasma calcium concentration and during elevation of the plasma calcium concentration produced by intra-arterial infusion of calcium chloride. Hypercalcemia inhibited the vasodilator action of hypercapnic acidosis so that the effect was not apparent until venous blood pH decreased below 7. The dilator effect of local application of acidified Ringer's solution on arterioles of the cremaster muscle of the rat was also inhibited by elevation of the plasma calcium concentration induced by intravenous administration of calcium chloride. The available evidence suggests that this inhibition of the dilator effect of hypercapnic acidosis by calcium ions is related to competition between calcium and hydrogen ions for binding at one or more cellular sites such as the sarcolemma, the sarcoplasmic reticulum, or the contractile proteins of vascular smooth muscle.