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 upo n the diameter of a vessel and its location. The purpose of the presen t investigation was to determine if the biochemical characteristics of the Na+-Ca2+ exchanger and the Ca2+ channel differ in sarcolemmal mem brane preparations isolated from a large conduit vessel (thoracic aort a) or from large and small coronary arteries. We also investigated the possibility of differences between sarcolemmal membranes isolated fro m coronary arteries dissected from the right and left ventricles. The purification of the sarcolemmal membranes was of a similar magnitude a mongst the different groups. Contamination of the sarcolemmal membrane s with other membranous organelles was negligible and similar amongst the groups. The K-m and V-max of Na+-dependent Ca2+ uptake in sarcolem mal vesicles was similar amongst the groups. Calcium channel character istics were examined by measuring [H-3] PN200-110 binding to sarcolemm al vesicles. The right coronary artery membranes from both large and s mall caliber vessels exhibited a higher K-d and the small right corona ry artery sarcolemmal preparation had a lower maximal binding density for [H-3] PN200-110. The results suggest that the right coronary arter y, and in particular the small diameter right coronary artery, possess es altered Ca2+ channel characteristics in isolated sarcolemmal membra nes.