Contribution of the Na–K–Cl Cotransporter on GABA_AReceptor-Mediated Presynaptic Depolarization in Excitatory Nerve Terminals

Abstract

GABA(A) receptor-mediated responses manifest as either hyperpolarization or depolarization according to the intracellular Cl(-) concentration ([Cl(-)](i)). Here, we report a novel functional interaction between the Na-K-Cl cotransporter (NKCC) and GABA(A) receptor actions on glutamatergic presynaptic nerve terminals projecting to ventromedial hypothalamic (VMH) neurons. The activation of presynaptic GABA(A) receptors depolarizes the presynaptic nerve terminals and facilitates spontaneous glutamate release by activating TTX-sensitive Na(+) channels and high-threshold Ca(2+) channels. This depolarizing action of GABA was caused by an outwardly directed Cl(-) driving force for GABA(A) receptors; that is, the [Cl(-)](i) of glutamatergic nerve terminals was higher than that predicted for a passive distribution. The higher [Cl(-)](i) was generated by bumetanide-sensitive NKCCs and was responsible for the GABA-induced presynaptic depolarization. Thus, GABA(A) receptor-mediated modulation of spontaneous glutamatergic transmission may contribute to the development and regulation of VMH function as well as to the excitability of VMH neurons themselves.

Estimate of the Chloride Concentration in a Central Glutamatergic Terminal: A Gramicidin Perforated-Patch Study on the Calyx of Held

“…Neither bumetanide nor furosemide, blockers of the common somatic and dendritic Na ϩ -and K ϩ -dependent Cl Ϫ transporters, altered the Cl Ϫ concentration. This contrasts with glutamate terminals in the ventromedial hypothalamus where Cl Ϫ uptake was sensitive to these drugs (Jang et al, 2001), but is consistent with a study in the lateral superior olive, where NKCC1 was not responsible for accumulating Cl Ϫ in neonatal neuronal soma (Balakrishnan et al, 2003). Replacing intracellular K ϩ with Cs ϩ increased [Cl Ϫ ] i , suggesting the disruption of a Cl Ϫ transporter coupled to K ϩ transport (Kakazu et al, 2000), although it does not distinguish between alteration of inwardversus outward-directed transport.…”

“…Activation of presynaptic Cl Ϫ -permeable GABA or glycine receptors depolarizes terminals, leading to inhibition (Saridaki et al, 1989;Zhang and Jackson, 1993;Rudomin and Schmidt, 1999) or facilitation (Jang et al, 2001(Jang et al, , 2006Turecek and Trussell, 2001) of transmitter release; evidence suggests that the polarity of modulation depends on the amount of depolarization, which is partly determined by [Cl Ϫ ] i . In vitro biochemical experiments have shown that glutamate loading into synaptic vesicles is stimulated by low [Cl Ϫ ] (ϳ4 -10 mM) and inhibited by [Cl Ϫ ] Ͼϳ20 mM (Naito and Ueda, 1985;Tabb et al, 1992;Takamori et al, 2000;Varoqui et al, 2002).…”

Allopregnanolone enhancement of GABAergic transmission in rat medial preoptic area neurons

“…Immediately preceding dissociation, slices were transferred to a 35-mm culture dish (Primaria 3801, Becton Dickinson), and the region of the MPOA was identified under a binocular microscope (SMZ-1; Nikon). Details of the mechanical dissociation have been described previously (12). Briefly, mechanical dissociation was accomplished using a custom-built vibration device and a fire-polished glass pipette oscillating at a frequency of ϳ3-5 Hz (0.1-0.2 mm).…”

The Chloride Transporter Na+-K+-Cl−Cotransporter Isoform-1 Contributes to Intracellular Chloride Increases afterIn VitroIschemia

“…NKCC-1 is the isoform of NKCC that is expressed ubiquitously in the brain and in other tissues; NKCC-2, the other isoform of this transporter, is expressed only in the kidney (Russell, 2000). This transporter helps maintain the Cl Ϫ gradient in neurons and is hypothesized to influence neuronal excitability through the regulation of [Cl Ϫ ] i (Sung et al, 2000;Jang et al, 2001;Beck et al, 2003). For instance, NKCC-1 activity is believed to be primarily responsible for depolarizing responses produced by GABA A receptors in dorsal root ganglion neurons (Alvarez-Leefmans et al, 1988, 2001Sung et al, 2000) and odorant receptors in olfactory receptor neurons (Reisert et al, 2005).…”