RT Journal Article SR Electronic T1 Bicuculline and Gabazine Are Allosteric Inhibitors of Channel Opening of the GABAA Receptor JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 625 OP 634 DO 10.1523/JNEUROSCI.17-02-00625.1997 VO 17 IS 2 A1 Shinya Ueno A1 John Bracamontes A1 Chuck Zorumski A1 David S. Weiss A1 Joe Henry Steinbach YR 1997 UL http://www.jneurosci.org/content/17/2/625.abstract AB Anesthetic drugs are known to interact with GABAAreceptors, both to potentiate the effects of low concentrations of GABA and to directly gate open the ion channel in the absence of GABA; however, the site(s) involved in direct gating by these drugs is not known. We have studied the ability of alphaxalone (an anesthetic steroid) and pentobarbital (an anesthetic barbiturate) to directly activate recombinant GABAA receptors containing the α1, β2, and γ2L subunits. Steroid gating was not affected when either of two mutated β2 subunits [β2(Y157S) and β2(Y205S)] are incorporated into the receptors, although these subunits greatly reduce the affinity of GABA binding. These observations indicate that steroid binding and subsequent channel gating do not require these particular residues, as already shown for barbiturates. Bicuculline or gabazine (two competitive antagonists of GABA binding) reduced the currents elicited by alphaxalone and pentobarbital from wild-type GABAA receptors; however, gabazine produced only a partial block of responses to pentobarbital or alphaxalone, and bicuculline only partially blocked responses to pentobarbital. These observations indicate that the blockers do not compete with alphaxalone or pentobarbital for a single class of sites on the GABAAreceptor. Finally, at receptors containing α1β2(Y157S)γ2L subunits, both bicuculline and gabazine showed weak agonist activity and actually potentiated responses to alphaxalone. These observations indicate that the blocking drugs can produce allosteric changes in GABAA receptors, at least those containing this mutated β2 subunit. We conclude that the sites for binding steroids and barbiturates do not overlap with the GABA-binding site. Furthermore, neither gabazine nor bicuculline competes for binding at the steroid or barbiturate sites. The data are consistent with a model in which both gabazine and bicuculline act as allosteric inhibitors of channel opening for the GABAA receptor after binding to the GABA-binding site.