Electrical and G-protein Regulation of CaV2.2 (N-type) Channels

Abstract

How G-proteins inhibit N-type, voltage-gated, calcium-selective channels (CaV2.2) during presynaptic inhibition is a decades-old question. G-proteins G{beta}{gamma} bind to intracellular CaV2.2 regions, but the inhibition is voltage-dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that G{beta}{gamma} acts by selectively inhibiting a subset of the four different CaV2.2 voltage-sensor domains (VSDs I-IV). During regular "willing" gating, VSDs I and IV activation resemble pore opening, VSD III activation is hyperpolarized, and VSD II appears unresponsive to depolarization. In the presence of G{beta}{gamma}, CaV2.2 gating is "reluctant": pore opening and VSD-I activation are strongly and proportionally inhibited, VSD IV is modestly inhibited while VSD III is not. We propose that G{beta}{gamma} inhibition of VSD-I and -IV underlies reluctant CaV2.2 gating and subsequent presynaptic inhibition.