M-SULFONATE BENZENE DIAZONIUM CHLORIDE - A NOVEL GABA(A) RECEPTOR ANTAGONIST

A previously identified irreversible affinity label for the gamma-amin obutyric acid (GABA) binding site in rat brain membranes, m-sulphonate benzene diazonium chloride (MSBD), was characterized in functional st udies using patch clamp and two-electrode voltage clamp recording tech niques. MSBD did not exhibit any agonist activity on native GABA(A) re ceptors in cultured sympathetic ganglionic neurones but acted as an an tagonist of GABA-induced membrane currents. Recombinant GABA(A) recept ors composed of alpha 1, beta 1 and gamma 2S subunits were expressed i n Xenopus oocytes following microinjection with cDNAs. Equilibrium dos e-response curve analyses established that MSBD was a partially revers ible, apparently non-competitive GABA(A) receptor antagonist. The IC50 for MSBD was estimated from an inhibition curve as 87 +/- 3 mu M. In addition, the onset and recovery from MSBD-induced inhibition was inde pendent of GABA(A) receptor activation. The relatively simple structur e of this novel GABA(A) receptor antagonist, MSBD, is compared with kn own agonists and antagonists at the GABA(A) receptor. MSBD may be a us eful pharmacological tool which could be used to deduce further inform ation about the structure and function of agonist and antagonist bindi ng sites on the GABA(A) receptor.