The main determinant of furosemide inhibition on GABA(A) receptors is located close to the first transmembrane domain.

Inhibitory GABA(A) receptors are regulated by numerous allosteric modulators, the most receptor-subtype specific of which is furosemide. It recognises receptors of the subunit composition alpha6beta2/3gamma2, restricted to cerebellar granule cells. To locate furosemide's site of action we constructed chimeras of the furosemide-sensitive alpha6 and the furosemide-insensitive alpha1 subunit, and expressed and studied them together with the beta3 and gamma2 subunits in Xenopus oocytes by the two-electrode voltage clamp technique. The inhibition of GABA-induced currents by furosemide mainly depended on a short domain proximal to the first transmembrane region of the alpha6 subunit.