The PDZ-binding motif of the beta2-adrenoceptor is essential for physiologic signaling and trafficking in cardiac myocytes

β 1 - and β 2 -adrenergic receptors (AR) regulate cardiac myocyte function through distinct signaling pathways. In addition to regulating cardiac rate and contractility, β 1 AR and β 2 AR may play different roles in the pathogenesis of heart failure. Studies on neonatal cardiac myocytes from β 1 AR and β 2 AR knockout mice suggest that subtype-specific signaling is determined by subtype-specific membrane targeting and trafficking. Stimulation of β 2 ARs has a biphasic effect on contraction rate, with an initial increase followed by a sustained G i -dependent decrease. Recent studies show that a PDZ domain-binding motif at the carboxyl terminus of human β 2 AR interacts with ezrin-binding protein 50/sodium–hydrogen exchanger regulatory factor, a PDZ-domain-containing protein. The human β 2 AR carboxyl terminus also binds to N -ethylmaleimide-sensitive factor, which does not contain a PDZ domain. We found that mutation of the three carboxyl-terminal amino acids in the mouse β 2 AR (β 2 AR-AAA) disrupts recycling of the receptor after agonist-induced internalization in cardiac myocytes. Nevertheless, stimulation of the β 2 AR-AAA produced a greater contraction rate increase than that of the wild-type β 2 AR. This enhanced stimulation of contraction rate can be attributed in part to the failure of the β 2 AR-AAA to couple to G i . We also observed that coupling of endogenous, wild-type β 2 AR to G i in β 1 AR knockout myocytes is inhibited by treatment with a membrane-permeable peptide representing the β 2 AR carboxyl terminus. These studies demonstrate that association of the carboxyl terminus of the β 2 AR with ezrin-binding protein 50/sodium–hydrogen exchanger regulatory factor, N -ethylmaleimide-sensitive factor, or some related proteins dictates physiologic signaling specificity and trafficking in cardiac myocytes.