Monovalent and Divalent Ions in Vascular Tissue

Abstract

Steep transmembrane concentration gradients in vascular smooth muscle for all ions are maintained by energy-requiring pumps. The Na⁺ gradient appears to dominate the distribution of the other ions primarily because it controls cell hydration and energizes the transport of sugars, amino acids, and Ca⁺⁺, Mg⁺⁺, and H⁺. The Na⁺ gradient is a closely regulated constant (about ten to one) and is not perturbed except by changes in the limited permeability of the vascular smooth muscle membrane to Na⁺ or in the activity of its transport enzyme, the Na⁺-K⁺ATPase. Increased permeability to Na⁺ has been seen in vascular smooth muscle and in erythrocytes in salt-dependent forms of experimental hypertension, as well as in essential hypertension. A compensatory increase in Na⁺ transport (extrusion) has been seen. This increase in transport can be produced by a moderate increase in aldosterone acting alone or by a lesser increase acting synergistically with vasopressin.