Beta 2-adrenergic receptor regulation of the cardiac L-type Ca2+ channel coexpressed in a fibroblast cell line.

Abstract

To characterize the functional coupling of the beta 2-AR to the cardiac Ca2+ channel in a system with a single receptor subtype, we stably cotransfected a Chinese hamster fibroblast (CHW) cell line, which lacks 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 effects of beta 2-AR stimulation on the expressed Ca2+ channel current were examined using the whole-cell patch-clamp technique. CHW cells transfected with the Ca2+ channel subunits displayed a voltage-dependent inward current having properties typical of native cardiac L-type Ca2+ channels. The expressed current was increased by a phosphorylation-dependent mechanism. CHW cells cotransfected with the Ca2+ channel subunits and the beta 2-AR were responsive to isoproterenol (Iso) in a dose-dependent manner. Iso (10 microM) increased peak Ca2+ channel current to 172 +/- 5% (n = 17) of control amplitude, indicating that the expressed Ca2+ channels are functionally coupled to the beta 2-AR. The results demonstrate unequivocally that beta 2-ARs can modulate the activity of cardiac Ca2+ channels, independent of beta 1-ARs. The results also demonstrate the usefulness of the CHW heterologous expression system, the first to reconstitute physiological modulation of an L-type Ca2+ channel by the beta 2-AR, for studying receptor subtype-specific regulation of the Ca2+ channel.