Direct Inhibition of CaV2.3 by Gem Does Not Requiere a Direct Alpha1E/Beta Interaction

Abstract

and Gem/Kir (RGK) sub-family of small GTP-binding protein include e the most potent endogenous inhibitor of High-Voltage Activated (HVA) calcium channels. RGK proteins use several mechanisms to inhibit calcium current (I CA): i) they promote dynamin-dependent endocytocys; ii) the lower the Po of the channel: ii) and they voltage sensor or reduction of charge. All RGK proteins associate directly with Ca 2þ channel b subunits (Cavb), and the binding between CaVa1 / Cavb has been shown to be essential for their inhibitory action for CaV1.2 and Ca V 2.1 and Ca V 2.2. In this study, we investigated inhibition of Ca V 2.3 Ca 2þ channels by RGK proteins. We found that when Xenopus laevis oocytes expressing Cav2.3 channels were injected with purified Gem protein, but not Rem, calcium currents where significantly decreased. This reduction was accompanied by a right shift in the conductance-voltage (GV curve) relationship of the channel. Furthermore, Gem also decreases the number of channels in the plasma membrane, evidenced by a reduction in maximal charge movement after injection of purified protein. The kinetic and voltage dependence of the reduced charge movement was not affected and thus immobilization of a subset of voltage-sensor seems unlikely. Surprisingly both effects are not dependent on the binding between CaVa1 to Cavb since CaV2.3 were expressed alone. Thus unlike than other neuronal calcium channels, Gem inhibit Cav2.3 channels in a CaVb-independent manner and through two synergistic mechanisms: a increase in voltage for activation and a decrease in the number of channels.