RGK GTPase-dependent CaV2.1 Ca2+ channel inhibition is independent of CaVβ-subunit-induced current potentiation

RGK (Rad-Gem-Rem) GTPases have been described as potent negative regulators of the Ca2+ influx via high-threshold voltage-activated Ca2+ channels. Recent work, mostly performed on CaV1.2 Ca2+ channels, has highlighted the crucial role played by the channel auxiliary CaVβ subunits and identified several GTPase and β-subunit protein domains involved in this regulation. We now extend these conclusions by producing the first complete characterization of the effects of Gem, Rem, and Rem2 on the neuronal CaV2.1 Ca2+ channels expressed with CaVβ1 or CaVβ2 subunits. Current inhibition is limited to a decrease in amplitude with no modification in the voltage dependence or kinetics of the current. We demonstrate that this inhibition can occur for CaVβ constructs with impaired capacity to induce current potentiation, but that it is lost for CaVβ constructs deleted for their β-interaction domain. The RGK C-terminal last ∼80 amino acids are sufficient to allow potent current inhibition and in vivo β-subunit/Gem intera...