G protein activation inhibits gating charge movement in rat sympathetic neurons

Abstract

G protein-coupled receptors (GPCRs) control neuronal functions via ion channel modulation. For voltage-gated ion channels, gating charge movement precedes and underlies channel opening. Therefore, we sought to investigate the effects of G protein activation on gating charge movement. Nonlinear capacitive currents were recorded using the whole cell patch-clamp technique in cultured rat sympathetic neurons. Our results show that gating charge movement depends on voltage with average Boltzmann parameters: maximum charge per unit of linear capacitance ( Qmax) = 6.1 ± 0.6 nC/μF, midpoint ( Vh) = −29.2 ± 0.5 mV, and measure of steepness ( k) = 8.4 ± 0.4 mV. Intracellular dialysis with GTPγS produces a nonreversible ∼34% decrease in Qmax, a ∼10 mV shift in Vh, and a ∼63% increase in k with respect to the control. Norepinephrine induces a ∼7 mV shift in Vh and ∼40% increase in k. Overexpression of G protein β1γ4 subunits produces a ∼13% decrease in Qmax, a ∼9 mV shift in Vh, and a ∼28% increase in k. We correlate charge movement modulation with the modulated behavior of voltage-gated channels. Concurrently, G protein activation by transmitters and GTPγS also inhibit both Na+ and N-type Ca2+ channels. These results reveal an inhibition of gating charge movement by G protein activation that parallels the inhibition of both Na+ and N-type Ca2+ currents. We propose that gating charge movement decrement may precede or accompany some forms of GPCR-mediated channel current inhibition or downregulation. This may be a common step in the GPCR-mediated inhibition of distinct populations of voltage-gated ion channels.