G protein activation inhibits gating charge movement in rat sympathetic neurons.
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 (Q(max)) = 6.1 +/- 0.6 nC/microF, midpoint (V(h)) = -29.2 +/- 0.5 mV, and measure of steepness (k) = 8.4 +/- 0.4 mV. Intracellular dialysis with GTPgammaS produces a nonreversible approximately 34% decrease in Q(max), a approximately 10 mV shift in V(h), and a approximately 63% increase in k with respect to the control. Norepinephrine induces a approximately 7 mV shift in V(h) and approximately 40% increase in k. Overexpression of G protein beta(1)gamma(4) subunits produces a approximately 13% decrease in Q(max), a approximately 9 mV shift in V(h), and a approximately 28% increase in k. We correlate charge movement modulation with the modulated behavior of voltage-gated channels. Concurrently, G protein activation by transmitters and GTPgammaS also inhibit both Na(+) and N-type Ca(2+) channels. These results reveal an inhibition of gating charge movement by G protein activation that parallels the inhibition of both Na(+) and N-type Ca(2+) 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.
Hernández-Ochoa
Erick O
EO
Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, México D. F., México.
García-Ferreiro
Rafael E
RE
García
David E
DE
D000320:Adrenergic Fibers / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism
D024642:Potassium Channels, Voltage-Gated; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012964:Sodium; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium