Modulation of brain Na+ channels by a G-protein-coupled pathway.

Abstract

Na+ channels in acutely dissociated rat hippocampal neurons and in Chinese hamster ovary (CHO) cells transfected with a cDNA encoding the a subunit of rat brain tpe IIA Na+ channel [14][15][16]. In heart, the opening of an inwardly rectifying K+ channel by muscarinic acetylcholine receptors requires GTP and a pertussis toxin (PTX)-sensitive G protein (17)(18)(19)(20), and 3-adrenergic receptors modulate Na+ channels by parallel pathways involving cAMP-dependent protein phosphorylation and possibly direct interaction with G, (21,22 EXPERIMENTAL PROCEDURES Cell Culture. Hippocampal neurons were acutely dissociated from 7-to 21-day-old Sprague-Dawley rats as described by Kuo and Bean (24). CNaIIA-1 cells were maintained as described (6).Electrophysiological Recording. Whole-cell voltage-clamp recordings (25) were obtained as described (6) using micropipettes with resistances of 1-2 Mfl in our internal solutions. Capacity transients were canceled and series resistance was compensated (>80%6) using the internal voltage-clamp circuitry. Remaining linear capacity transients as well as leakage currents were subtracted by the P/4 procedure. Conductance-voltage (g-V) relationships were calculated from peak current vs. voltage (I-V) relationships according to g = I/(V -Vr), where I is the peak current measured at voltage V, and Vr is the measured reversal potential. Normalized conductance-voltage relationships and inactivation curves were fit with a Boltzmann relation, 1/(1 + exp[(V -Vl/2)/k]), where

Computer simulations of high-pass filtering in zebrafish larval muscle fibres

“…The coordinates of the end of this line represent the steady-state values at which repetitive firing is obtained, and in the model this represents a convergence of the steady-state curves to bring about an increased overlap (Fig.·6). A number of studies have shown that some steady-state parameters and maximum current density of voltage-gated sodium channels can be modulated by intracellular enzymes such as tyrosine kinases and phosphatases (Alroy et al, 1999;Hilborn et al, 1998;Ratcliffe et al, 2000) or by second messengers such as Gprotein subunits (Ma et al, 1994(Ma et al, , 1997. However, the model reported here suggests that the inactivation rate of the sodium current must be at least quadrupled if the firing properties of the cell are to change from once-only firing to repetitive discharges.…”

Effects of Alcohols and Anesthetics on Recombinant Voltage-Gated Na+ Channels

“…Na ϩ channels can be modulated by PKA-and PKC-mediated phosphorylation (Cantrell and Catterall, 2001). Moreover, direct interaction of Na ϩ channels with G proteins might also modulate the function of Na ϩ channels (Ma et al, 1994(Ma et al, , 1997. Although propofol significantly inhibited the Na ϩ channels at the higher concentration, an important point is that propofol, at clinically relevant concentrations, did not show significant inhibition of Na ϩ channels expressed in Xenopus oocytes.…”

Activation of Go-proteins by Membrane Depolarization Traced by in Situ Photoaffinity Labeling of Gαo-proteins with [α32P]GTP-azidoanilide

“…Lanes 7 and 8, cross-linking in isolated membranes treated by GDP␤S (100 M) and by GTP␥S (100 M), respec- membrane potential and the activation of muscarinic (M1) receptors (72). Thus, in addition to activation of ion channels by stimulation of G-protein-coupled receptors (1,(73)(74)(75), receptor stimulation may be modulated by activation of voltage-gated ion channels. This in turn may result feedback mechanisms, producing long term changes in the membrane potential.…”