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- transporter 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 (EGABA) compared with the hippocampus proper or the neocortex. The NKCC1 blocker bumetanide or a temperature decrease of 10°C shifted the GABA-current FGABA 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.
|Number of pages||4|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - May 30 2006|
- Chloride transporter
- GABA receptors
- Xenopus oocytes
ASJC Scopus subject areas