Current modulation and membrane targeting of the calcium channel alpha(1c)Subunit are independent functions of the beta subunit

1. The beta subunits of voltage-sensitive calcium channels facilitate the i ncorporation of channels into the plasma, membrane and modulate calcium cur rents. In order to determine whether these two effects of the beta subunit are interdependent or independent of each other we studied plasma membrane incorporation of the channel subunits with green fluorescent protein and im munofluorescence labelling, and current modulation with whole-cell and sing le-channel patch-clamp recordings in transiently transfected human embryoni c kidney tsA201 cells. 2. Coexpression of rabbit cardiac muscle alpha(1C) with rabbit skeletal mus cle beta(1a), rabbit heart/brain beta(2a) or rat brain beta(3) subunits res ulted in the colocalization of alpha(1C) with beta and in a marked transloc ation of the channel complexes into the plasma membrane. In parallel, the w hole-cell current density and single-channel open probability were increase d. Furthermore, the beta(2a) isoform specifically altered the voltage depen dence of current activation and the inactivation kinetics. 3. A single amino acid substitution in the beta subunit interaction domain of alpha(1C) (alpha(1C) Y467S) disrupted the colocalization and plasma, mem brane targeting of both subunits without affecting the beta subunit-induced modulation of whole-cell currents and single-channel properties. 4. These results show that the modulation of calcium currents by beta subun its can be explained by beta subunit-induced changes of single-channel prop erties, but the formation of stable alpha(1C)-beta complexes and their incr eased incorporation into the plasma membrane appear not to be necessary for functional modulation.