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

ABSTRACT

How G-proteins inhibit N-type, voltage-gated, calcium-selective channels (Ca V 2.2) during presynaptic inhibition is a decades-old question. G-proteins Gßγ bind to intracellular Ca V 2.2 regions, but the inhibition is voltage-dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that Gßγ acts by selectively inhibiting a subset of the four different Ca V 2.2 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 Gßγ, Ca V 2.2 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 Gßγ inhibition of VSD-I and -IV underlies reluctant Ca V 2.2 gating and subsequent presynaptic inhibition.