NA2+-CA2+ EXCHANGE AND CA2+ CHANNEL CHARACTERISTICS IN BOVINE AORTA AND CORONARY-ARTERY SMOOTH-MUSCLE SARCOLEMMAL MEMBRANES

Tension generation and Ca2+ flux in smooth muscle varies depending upon the diameter of a vessel and its location. The purpose of the present investigation was to determine if the biochemical characteristics of the Na+-Ca2+ exchanger and the Ca2+ channel differ in sarcolemmal membrane preparations isolated from a large conduit vessel (thoracic aorta) or from large and small coronary arteries. We also investigated the possibility of differences between sarcolemmal membranes isolated from coronary arteries dissected from the right and left ventricles. The purification of the sarcolemmal membranes was of a similar magnitude amongst the different groups. Contamination of the sarcolemmal membranes with other membranous organelles was negligible and similar amongst the groups. The K-m and V-max of Na+-dependent Ca2+ uptake in sarcolemmal vesicles was similar amongst the groups. Calcium channel characteristics were examined by measuring [H-3] PN200-110 binding to sarcolemmal vesicles. The right coronary artery membranes from both large and small caliber vessels exhibited a higher K-d and the small right coronary artery sarcolemmal preparation had a lower maximal binding density for [H-3] PN200-110. The results suggest that the right coronary artery, and in particular the small diameter right coronary artery, possesses altered Ca2+ channel characteristics in isolated sarcolemmal membranes.