STUDIES ON THE INTRINSIC ACTIVITY (EFFICACY) OF HUMAN ADRENERGIC-RECEPTORS - COEXPRESSION OF BETA(1) AND BETA(2) REVEALS A LOWER EFFICACY FOR THE BETA(1) RECEPTOR

Through co-expression of the human beta1 and beta2 adrenergic receptors in a single tester cell (the murine L fibroblast) and through assaying the effect of the beta1 and beta2 selective blockers CGP 20712A and ICI 118551 on isoproterenol-stimulated adenylyl cyclase, it is shown that the maximal stimulation achievable with a given cell density of beta1 adrenergic receptor is less than that obtained with the same density of the beta2 adrenergic receptor It is concluded that the efficacy of the 2 receptors differs in that the beta1 adrenergic receptor has a lower efficacy (or intrinsic activity) than does the beta2 adrenergic receptor.