DIFFERENTIAL DISTRIBUTION OF BETA-1 AND BETA-2 ADRENERGIC-RECEPTORS IN CAT AND GUINEA-PIG HEART

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 2 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 1/4 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 contained twice as many receptors of the .beta.-1 type than did the ventricle of the guinea-pig heart. .beta.-2 selective drugs have more of an effect on chronotropy than on inotropy.