ClC-2 Voltage-Gated Channels Constitute Part of the Background Conductance and Assist Chloride Extrusion

Abstract

The function of voltage-gated chloride channels in neurons is essentially unknown. The voltage-gated chloride channel ClC-2 mediates a chloride current in pyramidal cells of the hippocampus. We directly show that ClC-2 assists chloride extrusion after high chloride load. Furthermore, the loss of this chloride channel leads to a dramatic increase of the input resistance of CA1 pyramidal cells, making these cells more excitable. Surprisingly, basal synaptic transmission, as judged from recordings of field EPSPs, was decreased. This difference was eliminated when GABAergic inhibition was blocked. Recordings from hippocampal interneurons revealed ClC-2-mediated currents in a subset of these cells. An observed increase in GABAergic inhibition could thus be explained by an increase in the excitability of interneurons, caused by the loss of ClC-2. Together, we suggest a dual role for ClC-2 in neurons, providing an additional efflux pathway for chloride and constituting a substantial part of the background conductance, which regulates excitability. In ClC-2 knock-out mice, an increased inhibition seemingly balances the hyperexcitability of the network and thereby prevents epilepsy.

ClC-2 Channels Regulate Neuronal Excitability, Not Intracellular Chloride Levels

“…1C); this replicates Figure 2f of Földy et al (2010) and Figure 2 of Rinke et al (2010). To summarize, our model reproduced ClC-2 rectification properties (Staley, 1994) and the voltage-clamp data that are the basis for concluding that ClC-2 contributes to intracellular Cl Ϫ homeostasis (Földy et al, 2010;Rinke et al, 2010 (Fig. 1D).…”

“…Other cotransporters and exchangers may contribute to maintaining low [Cl Ϫ ] i , but ion channels are typically ill suited for this purpose because, when open, they let ions run down their gradients. Despite this, the voltage-and chloride-sensitive channel ClC-2 has been proposed to help regulate [Cl Ϫ ] i because inward rectification should, in principal, cause it to act as one-way Cl Ϫ exit valve (Staley, 1994;Földy et al, 2010;Rinke et al, 2010;Smart, 2010). Chloride efflux via ClC-2 nevertheless requires an appropriate driving force; specifically, E Cl must be less negative than (i.e., depolarized relative to) V. Those conditions exist when V is manipulated directly by voltage-clamp and high-Cl Ϫ pipette solutions and/or KCC2 blockade render E Cl unnaturally depolarized, but tend not to occur under physiological conditions.…”

“…Driving force normally promotes Cl Ϫ influx, which means an imperfect exit valve could leak Cl Ϫ into the cell. Indeed, experiments have suggested that ClC-2 reduces excitability by contributing to leak conductance (Madison et al, 1986;Rinke et al, 2010 To resolve these issues, we built a computational model that tracks V and [Cl Ϫ ] i using ClC-2 parameters characterized in CA1 pyramidal cells (Staley, 1994). After validating our model by comparison against past voltage-clamp experiments, we tested it under physiological conditions (i.e., in current clamp, without pipette dialysis, with KCC2 intact).…”

Brain white matter oedema due to ClC-2 chloride channel deficiency: an observational analytical study

“…1,5 Information about the localisation of ClC-2 within the brain comes from rodent studies, which have detected ClC-2 in oligodendrocytes, astrocytes (especially in endfeet), and pyramidal and non-pyramidal neurons in the hippocampus. 6,7 Evidence suggests that ClC-2 modulates postsynaptic responses to GABA by aff ecting intracellular chloride concentration in neurons 8 and that ClC-2 regulates neuronal excitability, 9,10 but the physiological relevance of these fi ndings has not been confi rmed.…”

Funktionen der GABAergen Übertragung im unreifen Gehirn

“…1A). Dieser ist in den meisten Neuronen des adulten ZNS durch den K + /Cl --Kotransporter KCC2 (SLC12A5) repräsentiert (Rivera et al, 1999;Hübner et al, 2001 (Rinke et al, 2010).…”