Multiple roles for the first transmembrane domain of GABA(A) receptor subunits in neurosteroid modulation and spontaneous channel activity

作者：Baker Carrie; Sturt Brianne L; Bamber Bruce A^*

来源：Neuroscience Letters, 2010, 473(3): 242-247.

DOI：10.1016/j.neulet.2010.02.058

• GABA(A) receptor
• Neurosteroid
• PS
• THDOC
• Direct activation
• Spontaneous opening

Neurosteroids exert potent physiological effects by allosterically modulating synaptic and extrasynaptic GABA(A) receptors. Some endogenous neurosteroids, such as 3 alpha, 21-dihydroxy-5 beta-pregnan-20-one (5 alpha, 3 alpha-THDOC), potentiate GABA(A) receptor function by interacting with a binding pocket defined by conserved residues in the first and fourth transmembrane (TM) domains of alpha subunits. Others, such as pregnenolone sulfate (PS), inhibit GABA(A) receptor function through as-yet unidentified binding sites. Here we investigate the mechanisms of PS inhibition of mammalian GABA(A) receptors, based on studies of PS inhibition of the UNC-49 GABA receptor, a GABA(A)-like receptor from Caenorhabditis elegans. In UNC-49, a 19 residue segment of TM1 can be mutated to increase or decrease PS sensitivity over a 20-fold range. Surprisingly, substituting these UNC-49 sequences into mammalian alpha(1), beta(2), and gamma(2) subunits did not produce the corresponding effects on PS sensitivity of the resulting chimeric receptors. Therefore, it is unlikely that a conserved PS binding pocket is formed at this site. However we observed several interesting unexpected effects. First, chimeric gamma(2) subunits caused increased efficacy of 5 alpha, 3 alpha-THDOC potentiation; second, spontaneous gating of alpha(6)beta(2)delta receptors was blocked by PS, and reduced by chimeric beta(2) subunits; and third, direct activation of alpha(6)beta(2)delta receptors by 5 alpha, 3 alpha-THDOC was reduced by chimeric beta(2) subunits. These results reveal novel roles for non-alpha subunits in neurosteroid modulation and direct activation, and show that the beta subunit TM1 domain is important for spontaneous activity of extrasynaptic GABAA receptors.

• 出版日期2010-4-12