Abstract

beta-Adrenergic receptor (beta AR) agonists modulate a number of intracellular effectors; for example, they stimulate adenylyl cyclase and Ca2+ channels, inhibit Na+ channels and Mg2+ efflux, and activate Na-H exchange. Regulation of adenylyl cyclase, Ca2+, Na+, and Mg2+ by the beta AR is mediated through receptor coupling to the GTP-binding protein Gs. We have previously determined, however, that beta AR stimulation of Na-H exchange occurs independently of receptor coupling to Gs. In the present study, we analyzed mutant beta ARs containing deletions of amino acid residues within the third cytoplasmic domain, to determine whether there is a structural basis for the ability of the beta AR to couple divergently to the Gs-dependent stimulation of adenylyl cyclase and the Gs-independent activation of Na-H exchange. Receptor constructs with deletions of residues 222-229 and 258-270, which were previously shown to be defective in coupling to Gs and adenylyl cyclase, retained an isoproterenol-induced activation of Na-H exchange that was similar in time course and magnitude to that observed with the wild-type beta AR. These results confirm our previous findings that the beta AR activates Na-H exchange independently of Gs, and they further suggest that distinct molecular determinants of the receptor divergently stimulate adenylyl cyclase and Na-H exchange.