Current modulation and membrane targeting of the calcium channel alpha1C subunit are independent functions of the beta subunit.

1. The beta subunits of voltage-sensitive calcium channels facilitate the incorporation of channels into the plasma membrane and modulate calcium currents. 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 immunofluorescence labelling, and current modulation with whole-cell and single-channel patch-clamp recordings in transiently transfected human embryonic kidney tsA201 cells. 2. Coexpression of rabbit cardiac muscle alpha1C with rabbit skeletal muscle beta1a, rabbit heart/brain beta2a or rat brain beta3 subunits resulted in the colocalization of alpha1C with beta and in a marked translocation of the channel complexes into the plasma membrane. In parallel, the whole-cell current density and single-channel open probability were increased. Furthermore, the beta2a isoform specifically altered the voltage dependence of current activation and the inactivation kinetics. 3. A single amino acid substitution in the beta subunit interaction domain of alpha1C (alpha1CY467S) disrupted the colocalization and plasma membrane 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 subunits can be explained by beta subunit-induced changes of single-channel properties, but the formation of stable alpha1C-beta complexes and their increased incorporation into the plasma membrane appear not to be necessary for functional modulation.