Stable Expression and Coupling of Cardiac L-Type Ca 2+ Channels With β 1 -Adrenoceptors

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Abstract
A number of neurotransmitters modulate cardiac dihydropyridine-sensitive L-type Ca2+ channels through several homologous G protein–coupled receptors. Previous studies that have examined receptor–Ca2+ channel interactions have suffered because of the coexpression of various receptor subtypes in native cells. To study the functional coupling of a particular receptor subtype to these channels, rabbit cardiac Ca2+ channel α1 and skeletal β and α2/δ subunits were stably expressed in baby hamster kidney cells. In this stable cell line, Ca2+ channels remained at high levels (>1000 fmol/mg protein, or 2700 channels per cell) over extended times. The expressed recombinant Ca2+ channels displayed the voltage dependence of activation and inactivation, unitary conductance, and pharmacology characteristic of native cardiac L-type Ca2+ channels. Subsequent coexpression of the β1-adrenoceptors (150 to 300 fmol/mg protein) with the Ca2+ channels resulted in cell responsiveness to the extracellular application of isoproterenol. These results indicate that heterogeneous expression in mammalian cells provides a useful system for studying both biophysical analysis of Ca2+ channel properties and receptor-coupled regulatory processes.