Dissecting the Molecular Determinants of GABA_A Receptors Current Rundown, a Hallmark of Refractory Human Epilepsy

GABA(A) receptors-(Rs) are fundamental for the maintenance of an efficient inhibitory function in the central nervous system (CNS). Their dysfunction is associated with a wide range of CNS disorders, many of which characterized by seizures and epilepsy. Recently, an increased use-dependent desensitization due to a repetitive GABA stimulation (GABA(A) current rundown) of GABA(A)Rs has been associated with drug-resistant temporal lobe epilepsy (TLE). Here, we aimed to investigate the molecular determinants of GABA(A) current rundown with two different heterologous expression systems (Xenopus oocytes and human embryonic kidney cells; HEK) which allowed us to manipulate receptor stoichiometry and to study the GABA(A) current rundown on different GABA(A)R configurations. To this purpose, we performed electrophysiology experiments using two-electrode voltage clamp in oocytes and confirming part of our results in HEK. We found that different degrees of GABA(A) current rundown can be associated with the expression of different GABA(A)R beta-subunits reaching the maximum current decrease when functional alpha 1 beta 2 receptors are expressed. Furthermore, the blockade of phosphatases can prevent the current rundown observed in alpha 1 beta 2 GABA(A)Rs. Since GABA(A)R represents one important therapeutic target in the treatment of human epilepsy, our results could open new perspectives on the therapeutic management of drug-resistant patients showing a GABAergic impairment.