SPARE BETA-ADRENOCEPTORS FOR INOTROPIC EFFECTS OF CATECHOLAMINES IN KITTEN VENTRICLE

β-Adrenoceptors of ventricular membranes of kitten heart were labelled reversibly with (-)-3H-propranolol (binding constant 6 nM). Bound (-)-3H-propranolol was displaced with β-adrenoceptor blocking agents and catecholamines. Displacement constants KD(M) of the blockers were of the same of magnitude as their constants KB obtained from the antagonism of inotropic effects of catecholamines in papillary muscels. KD's of catecholamines were, however, 2 orders of magnitude larger than concentrations causing half maximal inotropic effects, indicating large spare β-adrenoceptor capacity. © 1978 Springer-Verlag.