{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,22]],"date-time":"2026-02-22T04:29:52Z","timestamp":1771734592903,"version":"3.50.1"},"reference-count":71,"publisher":"Wiley","issue":"22","license":[{"start":{"date-parts":[[2015,11,14]],"date-time":"2015-11-14T00:00:00Z","timestamp":1447459200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["The Journal of Physiology"],"published-print":{"date-parts":[[2015,11,15]]},"abstract":"<jats:sec><jats:title>Key Points<\/jats:title><jats:p><jats:list list-type=\"bullet\"><jats:list-item><jats:p>Most barbiturates are anaesthetics but unexpectedly a few are convulsants whose mechanism of action is poorly understood.<\/jats:p><\/jats:list-item><jats:list-item><jats:p>We synthesized and characterized a novel pair of chiral barbiturates that are capable of photolabelling their binding sites on GABA<jats:sub>A<\/jats:sub>receptors. In mice the<jats:italic>S<\/jats:italic>\u2010enantiomer is a convulsant, but the<jats:italic>R<\/jats:italic>\u2010enantiomer is an anticonvulsant.<\/jats:p><\/jats:list-item><jats:list-item><jats:p>The convulsant<jats:italic>S<\/jats:italic>\u2010enantiomer binds solely at an inhibitory site. It is both an open state inhibitor and a resting state inhibitor. Its action is pH independent, suggesting the pyrimidine ring plays little part in binding. The inhibitory site is not enantioselective because the<jats:italic>R<\/jats:italic>\u2010enantiomer inhibits with equal affinity.<\/jats:p><\/jats:list-item><jats:list-item><jats:p>In contrast, only the anticonvulsant<jats:italic>R<\/jats:italic>\u2010enantiomer binds to the enhancing site on open channels, causing them to stay open longer. The enhancing site is enantioselective.<\/jats:p><\/jats:list-item><jats:list-item><jats:p>The<jats:italic>in vivo<\/jats:italic>actions of the convulsant<jats:italic>S<\/jats:italic>\u2010enantiomer are accounted for by its interactions with GABA<jats:sub>A<\/jats:sub>receptors.<\/jats:p><\/jats:list-item><\/jats:list><\/jats:p><\/jats:sec><jats:sec><jats:title>Abstract<\/jats:title><jats:p>Most barbiturates are anaesthetics but a few unexpectedly are convulsants. We recently located the anaesthetic sites on GABA<jats:sub>A<\/jats:sub>receptors (GABA<jats:sub>A<\/jats:sub>Rs) by photolabelling with an anaesthetic barbiturate. To apply the same strategy to locate the convulsant sites requires the creation and mechanistic characterization of a suitable agent. We synthesized enantiomers of a novel, photoactivable barbiturate, 1\u2010methyl\u20105\u2010propyly\u20105\u2010(m\u2010trifluoromethyldiazirinyl) phenyl barbituric acid (<jats:italic>m<\/jats:italic>TFD\u2010MPPB). In mice,<jats:italic>S\u2010m<\/jats:italic>TFD\u2010MPPB acted as a convulsant, whereas<jats:italic>R\u2010m<\/jats:italic>TFD\u2010MPPB acted as an anticonvulsant. Using patch clamp electrophysiology and fast solution exchange on recombinant human \u03b1<jats:sub>1<\/jats:sub>\u03b2<jats:sub>3<\/jats:sub>\u03b3<jats:sub>2L<\/jats:sub>GABA<jats:sub>A<\/jats:sub>Rs expressed in HEK cells, we found that<jats:italic>S\u2010m<\/jats:italic>TFD\u2010MPPB inhibited GABA\u2010induced currents, whereas<jats:italic>R\u2010m<\/jats:italic>TFD\u2010MPPB enhanced them.<jats:italic>S<\/jats:italic>\u2010<jats:italic>m<\/jats:italic>TFD\u2010MPPB caused inhibition by binding to either of two inhibitory sites on open channels with bimolecular kinetics. It also inhibited closed, resting state receptors at similar concentrations, decreasing the channel opening rate and shifting the GABA concentration\u2013response curve to the right.<jats:italic>R<\/jats:italic>\u2010<jats:italic>m<\/jats:italic>TFD\u2010MPPB, like most anaesthetics, enhanced receptor gating by rapidly binding to allosteric sites on open channels, initiating a rate\u2010limiting conformation change to stabilized open channel states. These states had slower closing rates, thus shifting the GABA concentration\u2013response curve to the left. Under conditions when most GABA<jats:sub>A<\/jats:sub>Rs were open, an inhibitory action of<jats:italic>R<\/jats:italic>\u2010<jats:italic>m<\/jats:italic>TFD\u2010MPPB was revealed that had a similar IC<jats:sub>50<\/jats:sub>to that of<jats:italic>S<\/jats:italic>\u2010<jats:italic>m<\/jats:italic>TFD\u2010MPPB. Thus, the inhibitory sites are not enantioselective, and the convulsant action of<jats:italic>S<\/jats:italic>\u2010<jats:italic>m<\/jats:italic>TFD\u2010MPPB results from its negligible affinity for the enhancing, anaesthetic sites. Interactions with these two classes of barbiturate binding sites on GABA<jats:sub>A<\/jats:sub>Rs underlie the enantiomers\u2019 different pharmacological activities in mice.<\/jats:p><\/jats:sec>","DOI":"10.1113\/jp270971","type":"journal-article","created":{"date-parts":[[2015,9,17]],"date-time":"2015-09-17T12:34:55Z","timestamp":1442493295000},"page":"4943-4961","source":"Crossref","is-referenced-by-count":10,"title":["Contrasting actions of a convulsant barbiturate and its anticonvulsant enantiomer on the \u03b1<sub>1<\/sub>\u03b2<sub>3<\/sub>\u03b3<sub>2L<\/sub>GABA<sub>A<\/sub>receptor account for their<i>in vivo<\/i>effects"],"prefix":"10.1113","volume":"593","author":[{"given":"Rooma","family":"Desai","sequence":"first","affiliation":[{"name":"Department of Anaesthesia, Critical Care and Pain Medicine Massachusetts General Hospital Boston MA 02114 USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Pavel 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