Abstract

The concentrations of beta-1 and beta-2 adrenergic receptors were determined in membranes prepared from the left ventricles and right atria of cat and guinea-pig hearts. The relative densities of the two receptor subtypes were determined by analyzing the kinetics of inhibition of specific [125I]iodohydroxybenzylpindolol binding by drugs previously found to show in vitro selectivity for beta-1 or beta-2 receptors. The right atria (including the sinoatrial node) from hearts of both species contained both beta-1 and beta-2 adrenergic receptors. Although beta-1 receptors predominated, approximately one-quarter of the beta adrenergic receptors in the atria were of the beta-2 subtype. The ventricles contained essentially only beta-1 adrenergic receptors. The densities of beta-1 and beta-2 adrenergic receptors were similar in the atria from both species. The cat left ventricle, however, contained twice as many receptors of the beta-1 type than did the ventricle of the guinea-pig heart. These results may explain previous findings that beta-2 selective drugs have more of an effect on chronotropy than on inotropy.