Inhibition of calcium by magnesium in the contraction of rat aortic smooth muscle. I. Mathematical model of calcium and magnesium binding.

A mathematical model of the effect of calcium and magnesium binding on muscle tension was developed. The model was tested on aortic smooth muscle tissue obtained from rats fed magnesium-sufficient (Mg: 650 ppm) and magnesium-deficient (Mg: 4.5 ppm) diets. Ca2+ binding constants of 2.51 X 10(3) and 2.3 X 10(3) M-1 were obtained for aortae from magnesium-sufficient and magnesium-deficient rats, respectively. The corresponding Mg2+ binding constants were 0.6 X 10(3) and 0.4 X 10(3) M-1. The data indicate that Mg2+ is a competitive inhibitor of Ca2+ in tension development in rat aortic smooth muscle tissue.