A critical GxxxA motif in the γ 6 calcium channel subunit mediates its inhibitory effect on Cav3.1 calcium current

The eight members of the calcium channel γ subunit family are integral membrane proteins that regulate the expression and behaviour of voltage and ligand gated ion channels. While a subgroup consisting of γ 2 , γ 3 , γ 4 and γ 8 (the TARPs) modulate AMPA receptor localization and function, the γ 1 and γ 6 subunits conform to the original description of these proteins as regulators of voltage gated calcium channels. We have previously shown that the γ 6 subunit is highly expressed in atrial myocytes and that it is capable of acting as a negative modulator of low voltage activated calcium current. In this study we extend our understanding of γ 6 subunit modulation of low voltage activated calcium current. Using engineered chimeric constructs, we demonstrate that the first transmembrane domain (TM1) of γ 6 is necessary for its inhibitory effect on Cav3.1 current. Mutational analysis is then used to identify a unique GxxxA motif within TM1 that is required for the function of the subunit strongly suggesting the involvement of helix–helix interactions in its effects. Results from co‐immunoprecipitation experiments confirm a physical association of γ 6 with the Cav3.1 channel in both HEK cells and atrial myocytes. Single channel analysis reveals that binding of γ 6 reduces channel availability for activation. Taken together, the results of this study provide both a molecular and a mechanistic framework for understanding the unique ability of the γ 6 calcium channel subunit to modulate low voltage activated (Cav3.1) calcium current density.