Abstract

A human beta-adrenergic receptor cDNA was transfected and expressed in transformed Chinese hamster fibroblasts (CHW). The expressed receptor exhibited a typical beta 2-adrenergic selectivity for agonists and antagonists as assessed by radioligand binding and adenylate cyclase activation. Guanine nucleotide-sensitive high affinity binding of the agonist, isoproterenol, indicated effective coupling of the expressed receptor to a guanine nucleotide-regulatory protein. The level of expression of beta 2-AR in various cell clones varied over 200-fold and was positively correlated with the levels of beta 2-AR mRNA. In cells expressing between 0.04 and 3.0 pmol of beta 2-AR/mg of membrane protein, the efficacy of isoproterenol for stimulating adenylate cyclase increased with increasing numbers of expressed receptors but reached a plateau and started to decrease in clones with higher beta 2-AR density (3.0-8.0 pmol/mg of membrane protein). Preincubation of beta 2-AR-expressing cells with isoproterenol for 15 min led to significant reduction in the level of isoproterenol-sensitive adenylate cyclase activity. This agonist-induced desensitization was also accompanied by phosphorylation of the beta 2-AR. These data indicate that the expressed human beta 2-AR displays typical functional characteristics of adenylate cyclase-coupled receptors including agonist-induced desensitization. Moreover, the availability of this series of cellular clones, which differ markedly in their density of beta 2-AR, provides a unique set of biological reagents for future studies of beta 2-AR function and regulation.