Brief Communication Characterization of /3j- and /32-Adrenoceptor Subtypes in the Rat Atrioventricular Node by Quantitative Autoradiography

We characterized /3-adrenoceptor subtypes in the atrioventricular node of the rat heart by quantitative autoradiography. Consecutive 16-/xm-thick sections from single rat hearts containing the atrioventricular node were incubated with increasing concentrations of [I]iodocyanopindolol. After exposure to [H]Ultrofilm, optical densities corresponding to the atrioventricular node were determined by computerized densitometry after comparison with [I]standards. The computer program LIGAND was used for analysis of receptor subtypes. Delineation of /3-adrenoceptor subtypes was achieved by incubating consecutive tissue sections with 50 pM [I]iodocyanopindolol in the presence of increasing concentrations of the /3,-selective antagonist atenolol or the /3,-selective antagonist ICI 118,551. The atrioventricular node contains a higher concentration of /3-adrenoceptors than the adjacent interventricular septum. We estimated that the proportions of /3,and /3,-adrenoceptors in the atrioventricular node were about 56% and 44% of the total binding capacity respectively. (Circulation Research 1988;62:173-177)