Anomalous levels of Cl ⁻ transporters in the hippocampal subiculum from temporal lobe epilepsy patients make GABA excitatory

Abstract

The mRNA levels of NKCC1, an inwardly directed Na + , K + -2Cl − cotransporter that facilitates the accumulation of intracellular Cl − , and of KCC2, an outwardly directed K + -Cl − cotransporter that extrudes Cl − , were studied in surgically resected brain specimens from drug-resistant temporal lobe (TL) epilepsy (TLE) patients. Quantitative RT-PCR analyses of the mRNAs extracted from the human TLE-associated brain regions revealed an up-regulation of NKCC1 mRNA and a down-regulation of KCC2 mRNA in the hippocampal subiculum, compared with the hippocampus proper or the TL neocortex, suggesting an abnormal transcription of Cl − transporters in the TLE subiculum. In parallel experiments, cell membranes isolated from the same TLE-associated brain regions were injected into Xenopus oocytes that rapidly incorporated human GABA A receptors into their surface membrane. The GABA currents elicited in oocytes injected with membranes from the subiculum had a more depolarized reversal potential ( E GABA ) compared with the hippocampus proper or the neocortex. The NKCC1 blocker bumetanide or a temperature decrease of 10°C shifted the GABA-current E GABA more negative in oocytes injected with membranes from TLE hippocampal subiculum, matching the E GABA of TL neocortex-injected oocytes. We conclude that the anomalous expression of both Cl − transporters, KCC1 and NKCC2, in TLE hippocampal subiculum probably causes altered Cl − transport in the “epileptic” neurons, as revealed in the microtransplanted Xenopus oocytes, and renders GABA aberrantly “exciting,” a feature that may contribute to the precipitation of epileptic seizures.

Perturbed Chloride Homeostasis and GABAergic Signaling in Human Temporal Lobe Epilepsy

“…NKCC1 mRNA and a downregulation of KCC2 mRNA in the human epileptic subiculum compared with hippocampus and lateral neocortex (Palma et al, 2006). Our results with the antagonist bumetanide (Fig.…”

Global Optogenetic Activation of Inhibitory Interneurons during Epileptiform Activity

“…Depolarization of neurons would bring them closer to AP generation, whereas larger GABA release would increase intracellular chloride accumulation at the beginning of light stimulation, when ChR2-positive interneurons are firing, thereby readily triggering APs in pyramidal neurons. Such a shift in outcome of GABA A receptor activation has been reported for other models of epilepsy (Traub et al, 1995;Barmashenko et al, 2011) and in tissue from human epilepsy patients (Palma et al, 2006;Huberfeld et al, 2007).…”

Chloride Accumulation Drives Volume Dynamics Underlying Cell Proliferation and Migration

“…For example, hippocampal neurons from drug resistant temporal lobe epilepsy patients exhibit alterations in the expression of chloride transporters resulting in hyperexcitability (Palma et al 2006) as also observed following cortical injury in pyramidal neurons (Jin et al 2005), and astrocytes increase their resting chloride conductance in the case of reactive gliosis (MacVicar et al 1989;Walz and Wuttke 1999). Additionally, cells of the major primary brain tumors, gliomas, have a significant resting conductance for Cl Ϫ , which has been shown to be important for both the extensive proliferation and invasive migration of these cells (Habela and Sontheimer 2007;).…”