Densitometric analysis of beta 1- and beta 2-adrenoceptors in guinea-pig atrioventricular conducting system.
Quantitative autoradiography was used to determine the densities of beta 1- and beta 2-adrenoceptors in the atrioventricular conducting system in guinea-pig. (-)[125I]Cyanopindolol (CYP) was used to label beta 1- and beta 2-adrenoceptors in the absence or presence of the beta 1-adrenoceptor selective antagonist CGP 20712A (100 nM) or the beta 2-adrenoceptor selective antagonist ICI 118,551 (70 nM) or the non-selective beta-adrenoceptor antagonist (-)-propranolol (1 microM). Protein in discrete anatomical regions was determined using a densitometric method based on the dye Coomassie brilliant blue G. In the atrioventricular conducting system the proportion of beta 2-adrenoceptors determined by inhibition of total (-)[125I]-CYP binding by CGP 20712A (100 nM) ranged from 32.5% (atrioventricular node) to 48.7% (left bundle branch). In the atrioventricular node (16.8 fmol/mg protein), bundle of His (12.1 fmol/mg protein), right (17.4 fmol/mg protein) and left (21.1 fmol/mg protein) bundle branches and Purkinje cells there was a higher density of beta 2-adrenoceptors than in the interventricular septum (8.4 fmol/mg protein) and right atria (8.3 fmol/mg protein). The medial smooth muscle of the aorta, aortic valve, adventitia of the aorta, nerve tissue, tricuspid and mitral valves contained only beta 2-adrenoceptors. It is speculated that the use of beta-adrenoceptor antagonists to control cardiac arrhythmias involving a defect in conduction in the atrioventricular node should take into consideration both beta 1- and beta 2-adrenoceptors.
Department of Pharmacology, University of Melbourne, Parkville, Vic., Australia.
P
P
Molenaar
F D
FD
Russell
T
T
Shimada
R J
RJ
Summers
D000319:Adrenergic beta-Antagonists; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000473:pathology; D001283:Atrioventricular Node / Q000032:analysis*; D001345:Autoradiography; D003720:Densitometry; D005260:Female; D006168:Guinea Pigs; D006329:Heart Conduction System / Q000032:analysis*; D008297:Male; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D011506:Proteins / Q000032:analysis*; D011689:Purkinje Cells; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D012394:Rosaniline Dyes; D013194:Staining and Labeling
D000319:Adrenergic beta-Antagonists; D011506:Proteins; D011943:Receptors, Adrenergic, beta; D012394:Rosaniline Dyes; C047975:cyanopindolol; D011433:Propranolol; D010869:Pindolol; C004692:coomassie Brilliant Blue