Autoradiographic localization and densitometric analysis of beta-1 and beta-2 adrenoceptors in the canine left anterior descending coronary artery.

The location and proportions of beta-1 and beta-2 adrenoceptors in canine coronary arteries (0.5-2 mm) has been examined by autoradiography. X-ray film and nuclear emulsion-coated coverslips were exposed to sections of coronary artery previously incubated with [125I]iodocyanopindolol (50 pM) in the absence and presence of ICI 118,551 (70 nM) to block beta-2 adrenoceptors, CGP 20712A (100 nM) to block beta-1 adrenoceptors or (-)-propranolol (1 microM) to define nonspecific binding. The medial smooth muscle of the coronary artery had an even distribution of beta-1 adrenoceptors and two populations of beta-2 adrenoceptors, one evenly distributed and the other highly localized. Beta-2 adrenoceptors were also located on nerve tissue and in the adventitia. There was no evidence for localization of beta adrenoceptors on endothelial cells. Quantitative autoradiography was performed using computer-assisted image processing and the program AVID. The binding of [125I]cyanopindolol was saturable (KD = 50 pM) and competition binding curves with the beta-1 selective antagonist CGP 20712A and beta-2 selective antagonist ICI 118,551 showed beta-1 and beta-2 adrenoceptors in the proportions of 85:15% in both 0.5- and 2-mm arteries.