Membranes and Synaptosomes Used to Investigate Synaptic GABAergic Currents in Epileptic Patients

Among the most prevalent neurological disorders, epilepsy affects about 1% of the population worldwide. We previously found, using human epileptic tissues, that GABAergic neurotransmission impairment is a key mechanism that drives the pathological phenomena that ultimately lead to generation and recurrence of seizures. Using both a "microtransplantation technique" and synaptosomes preparations from drug-resistant temporal lobe epilepsies (TLEs), we used the technique of two-electrode voltage clamp to record GABA-evoked currents, focusing selectively on the synaptic "fast inhibition" mediated by low-affinity GABA_A receptors. Here, we report that the use-dependent GABA current desensitization (i.e., GABA rundown, which is evoked by applying to the cells consecutive pulses of GABA, at high concentration), which is a distinguishing mark of TLE, is mainly dependent on a dysfunction that affects synaptic GABA_A receptors. In addition, using the same approaches, we recorded a depolarized GABA reversal potential in synaptosomes samples from the human epileptic subicula of TLE patients. These results, which confirm previous experiments using total membranes, suggest an altered chloride homeostasis in the synaptic area. Finally, the lack of a Zn²⁺ block of GABA-evoked currents using the synaptosomes supports the enrichment of "synaptic fast inhibitory" GABA_A receptors in this preparation. Altogether, our findings suggest a pathophysiological role of low-affinity GABA_A receptors at the synapse, especially during the fast and repetitive GABA release underlying recurrent seizures.