Phosphatase inhibitors remove the run-down of gamma-aminobutyric acid type A receptors in the human epileptic brain.

The properties of gamma-aminobutyric acid (GABA) type A receptors (GABA(A) receptors) microtransplanted from the human epileptic brain to the plasma membrane of Xenopus oocytes were compared with those recorded directly from neurons, or glial cells, in human brains slices. Cell membranes isolated from brain specimens, surgically obtained from six patients afflicted with drug-resistant temporal lobe epilepsy (TLE) were injected into frog oocytes. Within a few hours, these oocytes acquired GABA(A) receptors that generated GABA currents with an unusual run-down, which was inhibited by orthovanadate and okadaic acid. In contrast, receptors derived from membranes of a nonepileptic hippocampal uncus, membranes from mouse brain, or recombinant rat alpha 1 beta 2 gamma 2-GABA receptors exhibited a much less pronounced GABA-current run-down. Moreover, the GABA(A) receptors of pyramidal neurons in temporal neocortex slices from the same six epileptic patients exhibited a stronger run-down than the receptors of rat pyramidal neurons. Interestingly, the GABA(A) receptors of neighboring glial cells remained substantially stable after repetitive activation. Therefore, the excessive GABA-current run-down observed in the membrane-injected oocytes recapitulates essentially what occurs in neurons, rather than in glial cells. Quantitative RT-PCR analyses from the same TLE neocortex specimens revealed that GABA(A)-receptor beta 1, beta 2, beta 3, and gamma 2 subunit mRNAs were significantly overexpressed (8- to 33-fold) compared with control autopsy tissues. Our results suggest that an abnormal GABA-receptor subunit transcription in the TLE brain leads to the expression of run-down-enhanced GABA(A) receptors. Blockage of phosphatases stabilizes the TLE GABA(A) receptors and strengthens GABAergic inhibition. It may be that this process can be targeted to develop new treatments for intractable epilepsy.