Stable expression and coupling of cardiac L-type Ca²⁺ channels with β₁-adrenoceptors

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 sub-types 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.