Beta-adrenergic receptors in guinea-pig myocardial tissue

Stereospecific binding sites for (-) [3H]-alprenolol, a beta-adrenergic antagonist, have been identified in guinea-pig myocardial broken cell preparations. The concentration of the sites was 0.3 pmoles per mg of protein and the dissociation constant (at 37 degrees C) 10(-8) M. A close correlation between the ability of various beta-adrenergic antagonists to compete with tracer alprenolol binding and to block the response of isoprenaline-stimulated myocardial adenylate cyclase has been found. Low affinity sites for the labelled beta-adrenergic antagonist in contrast to stereospecific sites are heat stable and do not discriminate between the (-) and the (+) forms of the beta-adrenergic antagonists. Adenylate cyclase in guinea-pig myocardial tissue is poorly stimulated by isoprenaline or 5'-guanylylimidodiphosphate. This is attributed to a high basal activity which could be lowered by a preincubation at 37 degrees C.