MODULATION OF RECOMBINANT ALPHA(6)BETA(2)GAMMA(2) GABA(A) RECEPTORS BY NEUROACTIVE STEROIDS

The sensitivity of the recombinant alpha(6) beta(2) gamma(2) GABA(A) r eceptor expressed in HEK 293 cells to neuroactive steroids was studied . The steroids 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha-OH-DHP) , pregnenolone sulfate and 3 alpha-OH-DHP sulfate have different modul atory effects on [H-3]muscimol or [H-3]Ro15-4513 binding to the alpha( 6) beta(2) gamma(2) than to the alpha(1) beta(2) gamma(2) receptor. Bi nding of both radioactive ligands to the alpha(6) beta(2) gamma(2) rec eptor was maximally potentiated with each steroid used (10 nM) and dec reased with further increases in steroid concentration. Using whole-ce ll recording, the GABA response of clusters of transfected HEK 293 cel ls was strongly potentiated by 3 or 10 nM 3 alpha-OH-DHP. In contrast, this response was reduced by 100 nM 3 alpha-OH-DHP. This latter effec t appears to be related to the acceleration of the GABA response desen sitization, observed in isolated cells. 3 alpha-OH-DHP (10 or 100 nM) was able to activate a response in the absence of GABA. It is proposed that the interaction of neuroactive steroids with the alpha(6) beta(2 ) gamma(2) receptor involves at least two distinct binding sites. One of them might be located close to the GABA binding site.