Differential regulation of chloride homeostasis and GABAergic transmission in the thalamus

Abstract

The thalamus is important for sensory integration with the ventrobasal thalamus (VB) as relay controlled by GABAergic projections from the nucleus reticularis thalami (NRT). Depending on the [Cl−]i primarily set by cation-chloride-cotransporters, GABA is inhibitory or excitatory. There is evidence that VB and NRT differ in terms of GABA action, with classical hyperpolarization in VB due to the expression of the Cl− extruder KCC2 and depolarizing/excitatory GABA action in the NRT, where KCC2 expression is low and Cl− accumulation by the Cl− inward transporter NKCC1 has been postulated. However, data on NKCC1 expression and functional analysis of both transporters are missing. We show that KCC2-mediated Cl− extrusion set the [Cl−]i in VB, while NKCC1 did not contribute substantially to Cl− accumulation and depolarizing GABA action in the NRT. The finding that NKCC1 did not play a major role in NRT neurons is of high relevance for ongoing studies on the therapeutic use of NKCC1 inhibitors trying to compensate for a disease-induced up-regulation of NKCC1 that has been described for various brain regions and disease states like epilepsy and chronic pain. These data suggest that NKCC1 inhibitors might have no major effect on healthy NRT neurons due to limited NKCC1 function.

NKCC-1 mediated Cl− uptake in immature CA3 pyramidal neurons is sufficient to compensate phasic GABAergic inputs

“…However, to our knowledge a detailed investigation of the kinetic properties of Cl − -transport has only been published for Cajal-Retzius cells 4 and immature spinal-cord motoneurons 7 as well as for mature cultured hippocampal 23 and thalamic neurons 32 . Whereas in mature hippocampal neurons the [Cl − ] i relaxation upon a massive [Cl − ] i increase occurs rather fast within ~ 30s 23 , in immature neurons a rather inefficient Cl − -transport was observed 4 , 7 .…”

Ectopic GABAA receptor β3 subunit determines Cl−/‐ATPase and chloride transport in HEK 293FT cells

“…However, a dominant role of the cotransporter is unlikely since the time constant is still ~ 10 min or longer [41], while recovery of GABA A R conductance after desensitization occurs at a time constant around 15 s [19,38]. Furthermore, the NKCC1 can make a small contribution to Cl − accumulation and GABAergic transmission [42].…”

Enhanced Na+‐K+‐2Cl‐ cotransporter 1 underlies motor dysfunction in huntington's disease

“…To avoid perturbation of the intracellular chloride concentration, we evaluated the GABA reversal potential ( E GABA ) of medium spiny neurons (MSNs) using the gramicidin‐perforated patch‐clamp recordings, detailed in the SI Methods. Notably, monitoring membrane leakage is critical during the measurement of E GABA . The integrity of the perforated patch configuration was assessed in cells by adding Alexa Fluor 594 to the pipette solution.…”