Isolation of Plasma Membranes from Rat Mesenteric Veins: A Comparison of Their Physical and Biochemical Properties with Arterial Membranes

Abstract

Plasma membranes were isolated from smooth muscles of rat mesenteric veins. The plasma membrane fraction is relatively pure according to its morphological and enzymatic characteristics. The membrane distribution, enzymatic activities, as well as calcium accumulation by the plasma membrane fraction from venous smooth muscle were compared to those from arterial smooth muscle. The isolated venous smooth muscle plasma membranes formed primarily closed vesicles which were capable of accumulating Ca²⁺ in the presence of ATP suggesting active transport of Ca²⁺ across the membrane vesicles. Evidence obtained from several approaches by studying the effect of A23187, phosphate ions and hypotonic shock on the Ca²⁺ accumulation in the presence of ATP revealed that there is an active transport of Ca²⁺ across isolated vascular smooth muscle membrane vesicles in addition to binding of Ca²⁺. However, venous smooth muscle plasma membrane fraction appears to be different from arterial smooth muscle plasma membrane fraction in its lower activity of alkaline phosphatase, greater Ca²⁺ binding and lower Ca²⁺ transport. These and previous studies show that the plasma membrane of vascular muscles may play an important role in the steady state regulation of cellular calcium concentration during excitation-contraction coupling, especially in small arteries and veins.