Subunit-selective modulation of GABA(A) receptors by the non-steroidal anti-inflammatory agent, mefenamic acid
Por:
Halliwell R.F., Thomas P., Patten D., James C.H., Martinez-Torres A., Miledi R., Smart T.G.
Publicada:
1 ene 1999
Resumen:
Mefenamic acid (MFA) has anti-convulsant and pro-convulsant effects in vivo, and has been shown to potentiate and inhibit GABA(A) (?-aminobutyric acid) receptors in vitro. In this study, whole-cell currents were recorded from Xenopus oocytes and human embryonic kidney (HEK) cells expressing human recombinant GABA(A) receptors to resolve the molecular mechanisms by which MFA modulates GABA(A) receptor function. We demonstrate that MFA potentiated GABA-activated currents for ?1?2?2S (EC50 = 3.2 ± 0.5 ?M), but not for ?1?1?2S receptors. MFA also enhanced GABA-activated responses and directly activated ?1?2/?3 GABA(A) receptors, but inhibited responses to GABA on ?1?1 constructs (IC50 = 40 ± 7.2 ?M). A comparison of ?1, ?2 and ?3 subunits suggested that the positive modulatory action of MFA involved asparagine (N) 290 in the second transmembrane domain (TM2) of the ?2 and ?3 subunits. Mutation of N290 to serine (S) markedly reduced modulation by MFA in ?1?2(N290S)?2S receptors, whereas ?1?1(S290N)?2S constructs revealed potentiated responses to GABA (EC50 = 7.8 ± 1.7 ?M) and direct activation by MFA. The potentiation by MFA displayed voltage sensitivity. The direct activation, potentiation and inhibitory aspects of MFA action were predominantly conferred by the ? subunits as the spontaneously active homomeric ?1 and ?3 receptors were susceptible to modulation by MFA. Molecular comparisons of MFA, loreclezole and etomidate, agents which exhibit similar selectivity for GABA(A) receptors, revealed their ability to adopt similar structural conformations. This study indicates that N290 in TM2 of ?2 and ?3 subunits is important for the regulation of GABA(A) receptor function by MFA. Our data provide a potential molecular mechanism for the complex central effects of MFA in vivo.
Filiaciones:
Halliwell R.F.:
Dept. of Biological Sciences, University of Durham, South Road, Durham, United Kingdom
Thomas P.:
Dept. of Pharmacology, School of Pharmacy, 29-39 Brunswick Square, London, United Kingdom
Patten D.:
Dept. of Biological Sciences, University of Durham, South Road, Durham, United Kingdom
James C.H.:
Dept. of Pharmaceutical Chemistry, School of Pharmacy, 29-39 Brunswick Square, London, United Kingdom
Martinez-Torres A.:
Laboratory of Cellular and Molecular Neurobiology, Dept. of Psychobiology, University of California, Irvine, CA, United States
Miledi R.:
Laboratory of Cellular and Molecular Neurobiology, Dept. of Psychobiology, University of California, Irvine, CA, United States
Smart T.G.:
Dept. of Pharmacology, School of Pharmacy, 29-39 Brunswick Square, London, United Kingdom
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