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This Article Full Text Full Text (PDF) All Versions of this Article: 567/2/365    most recent jphysiol.2005.088823v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wilkins, M. E. Articles by Smart, T. G. Search for Related Content PubMed PubMed Citation Articles by Wilkins, M. E. Articles by Smart, T. G.

¹ Department of Pharmacology, University College London, Medical Sciences Building, Gower Street, London WC1E 6BT, UK

Regulation of GABA_A receptors by extracellular pH exhibits a dependence on the receptor subunit composition. To date, the molecular mechanism responsible for the modulation of GABA_A receptors at alkaline pH has remained elusive. We report here that the GABA-activated current can be potentiated at pH 8.4 for both ß and ß subunit-containing receptors, but only at GABA concentrations below the EC₄₀. Site-specific mutagenesis revealed that a single lysine residue, K279 in the ß subunit TM2–TM3 linker, was critically important for alkaline pH to modulate the function of both 1ß2 and 1ß22 receptors. The ability of low concentrations of GABA to reveal different pH titration profiles for GABA_A receptors was also examined at acidic pH. At pH 6.4, GABA activation of ß receptors was enhanced at low GABA concentrations. This effect was ablated by the mutation H267A in the ß subunit. Decreasing the pH further to 5.4 inhibited GABA responses via ß receptors, whereas those responses recorded from ß receptors were potentiated. Inserting homologous ß subunit residues into the 2 subunit to recreate, in ß receptors, the proton modulatory profile of ß receptors, established that in the presence of ß2^H267, the mutation 2^T294K was necessary to potentiate the GABA response at pH 5.4. This residue, T294, is homologous to K279 in the ß subunit and suggests that a lysine at this position is an important residue for mediating the allosteric effects of both acidic and alkaline pH changes, rather than forming a direct site for protonation within the GABA_A receptor.

(Received 18 April 2005; accepted after revision 3 June 2005; first published online 9 June 2005)
Corresponding author T.G. Smart: Department of Pharmacology, University College London, Medical Sciences Building, Gower Street, London WC1E 6BT, UK. Email: t.smart{at}ucl.ac.uk