On the Existence of a Na†-Ca2† Exchange System in the Cell Membrane of Vascular Smooth Muscle

Publisher Website
Google Scholar
Abstract
Summary: Ca2† uptake was studied in Na†-loaded cell membrane vesicles isolated from blood vessels of several species. A rapid uptake of Ca2† was observed in an isotonic KCI medium when there was an outwardly directed Na† concentration gradient created across the membrane. Elimination of the Na† concentration gradient by including Na† or the sodium ionophore monensin in the assay medium resulted in drastic reduction of Ca2† uptake in the vesicles. This Ca2† uptake was found to be specific for Na† since other monovalent cations did not substitute Na†. Employing this approach, a Na†-Ca2† exchange system was demonstrated in dog mesenteric artery, rat mesenteric artery, rat aorta, and rabbit aorta. The apparent Km for free Ca2† of this process in these smooth muscles varies from 1.61 to 2.72 μM and the apparent maximum velocity varies from 7 to 16 nmol/min/mg protein. The results of the study with isolated membrane vesicles indicate the existence of a Na†-Ca2† exchange in the cell membrane of vascular smooth muscle.

This publication has 0 references indexed in Scilit: