Calcium current modulation by the γ1 subunit depends on alternative splicing of CaV1.1

Area of Science:

• Molecular and Cellular Physiology
• Ion Channel Function and Regulation

Background:

• Skeletal muscle voltage-gated calcium channel CaV1.1 is essential for excitation-contraction coupling.
• CaV1.1 function is modulated by its pore-forming α1S subunit and auxiliary subunits (α2δ-1, γ1).
• Alternative splicing of exon 29 in CaV1.1a alters its properties, reducing current density and shifting activation.

Purpose of the Study:

• To investigate the role of the γ1 subunit in modulating CaV1.1 splice variant function.
• To elucidate the mechanism by which exon 29 inclusion affects CaV1.1 current density and voltage dependence.

Main Methods:

• Generation of HEK293 cell lines stably expressing CaV1.1 splice variants (CaV1.1a, CaV1.1e) and auxiliary subunits (α2δ-1, β3, STAC3).
• Electrophysiological recordings to measure current density and voltage dependence of activation and inactivation.
• Molecular structure modeling to predict interactions between CaV1.1 and γ1 subunits.

Main Results:

• Coexpression of γ1 with CaV1.1a, but not CaV1.1e, significantly reduced current density (>50%).
• γ1 shifted the voltage dependence of inactivation to negative potentials for both splice variants.
• Structural modeling suggested direct interactions, but alanine substitutions did not abolish the γ1-dependent current reduction, indicating an allosteric mechanism.

Conclusions:

• The γ1 subunit's current-reducing effect on CaV1.1 is specifically dependent on the inclusion of exon 29.
• Exon 29 inclusion likely induces structural rearrangements in CaV1.1a that allosterically enhance γ1's inhibitory action.
• This study reveals a novel regulatory mechanism for skeletal muscle calcium channel function critical for physiological processes.