BETA(2)-ADRENERGIC RECEPTOR REGULATION OF THE CARDIAC L-TYPE CA2-LINE( CHANNEL COEXPRESSED IN A FIBROBLAST CELL)

To characterize the functional coupling of the beta(2)-AR to the cardi ac Ca2+ channel in a system with a single receptor subtype, we stably cotransfected a Chinese hamster fibroblast (CHW) cell line, which lack s beta(2)-ARs and Ca2+ channels, with the rabbit cardiac Ca2+ channel alpha(1) and beta(2) subunits and the human beta(2)-AR cDNAs. The effe cts of beta(2)-AR stimulation on the expressed Ca2+ channel current we re examined using the whole-cell patch-clamp technique. CHW cells tran sfected with the Ca2+ channel subunits displayed a voltage-dependent i nward current having properties typical of native cardiac L-type Ca2channels. The expressed current was increased by a phosphorylation-dep endent mechanism. CHW cells cotransfected with the Ca2+ channel subuni ts and the beta(2)-AR were responsive to isoproterenol (Iso) in a dose -dependent manner. Iso (10 mu M) increased peak Ca2+ channel current t o 172 +/- 5% (n = 17) of control amplitude, indicating that the expres sed Ca2+ channels are functionally coupled to the beta(2)-AR. The resu lts demonstrate unequivocally that beta(2)-ARs can modulate the activi ty of cardiac Ca2+ channels, independent of beta(1)-ARs. The results a lso demonstrate the usefulness of the CHW heterologous expression syst em, the first to reconstitute physiological modulation of an L-type Ca 2+ channel by the beta(2)-AR, for studying receptor subtype-specific r egulation of the Ca2+ channel.