Deficiency of external Ca and Mg increases membrane permeability in the vascular smooth muscle of rabbit aorta.

Effects of a 60 min incubation in Ca- and/or Mg-deficient solutions on the ion contents in vascular smooth muscle of rabbit aorta were examined. In Mg-deficient solution, resting tone of the muscle did not change. Ca-deficient solution increased, whereas Ca- and Mg-deficient solution decreased the resting tone. Ca-deficient solution increased and Ca- and Mg-deficient solution further increased cellular Na content whereas Ca-deficient solution decreased and Ca- and Mg-deficient solution further decreased the cellular K content. Mg-deficient solution did not change the ion contents. Application of hyperosmotic 160 mM NaCl elicited a contraction and a decrease in wet weight of the tissue in normal and Mg-deficient solutions. In Ca-deficient solution both the contraction and the loss of wet weight were attenuated. In Ca- and Mg-deficient solution, the contraction became smaller and the change in the wet weight was not observed. Loss of tissue Mg in Mg-deficient solution was increased when Ca was removed from the medium. Cellular 45Ca uptake increased after a 60 min treatment of the muscle in Ca-deficient solution and in Ca- and Mg-deficient solution. It is concluded that Ca- and Mg-depletion increases membrane permeability to mono- and divalent cations in rabbit aorta. Although Mg depletion alone does not seem to change the membrane permeability, Mg decreases the membrane permeability in the absence of Ca.