PT  - JOURNAL ARTICLE
AU  - P Molenaar
AU  - E Canale
AU  - R J Summers
TI  - Autoradiographic localization of beta-1 and beta-2 adrenoceptors in guinea pig atrium and regions of the conducting system.
DP  - 1987 Jun 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1048--1064
VI  - 241
IP  - 3
4099  - http://jpet.aspetjournals.org/content/241/3/1048.short
4100  - http://jpet.aspetjournals.org/content/241/3/1048.full
SO  - J Pharmacol Exp Ther1987 Jun 01; 241
AB  - [125I]Cyanopindolol binding to slide mounted guinea pig atrial sections was time-dependent (Ki = 2.4 X 10(8) M-1 min-1, K-1 = 1.2 X 10(-3) min-1) saturable (24-32 pM) and stereoselective with respect to the isomers of propranolol. Competition binding curves with the beta-1 selective antagonist CGP 20712A and beta-2 selective antagonist ICI 118,551 revealed the presence of beta-1 and beta-2 adrenoceptors in the proportions of 85 to 15%. X-ray film exposed to sections of guinea pig heart incubated previously with [125I]cyanopindolol with or without ICI 118,551 (70 nM) or CGP 20712A (100 nM) or (-)-propranolol (1 microM) showed a high density and even distribution of beta-1 adrenoceptors and a lower density and even distribution of beta-2 adrenoceptors over the myocardium. Beta-2 adrenoceptors also were located in the epicardium, the adventitia of the pulmonary artery, aorta, superior and inferior vena cava and the endothelium of the superior and inferior vena cava. Development of nuclear emulsion-coated coverslips confirmed these observations and, in addition, localized beta-2 adrenoceptors to nerve tissue and the aortic valve. In the papillary muscle and surrounding Purkinje cells there was a high density and even distribution of beta-1 and a much lower density of beta-2 adrenoceptors. The atrioventricular node, atrioventricular bundle and ventricular Purkinje system also contained both beta-1 and beta-2 adrenoceptors and in comparison with the surrounding myocardium, these tissues had a slightly greater density of beta-2 adrenoceptors.