RT Journal Article
SR Electronic
T1 Lactone Modulation of the γ-Aminobutyric Acid A Receptor: Evidence for a Positive Modulatory Site
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 114
OP 119
DO 10.1124/mol.52.1.114
VO 52
IS 1
A1 Williams, Korwyn L.
A1 Tucker, Joseph B.
A1 White, Geoffrey
A1 Weiss, David S.
A1 Ferrendelli, James A.
A1 Covey, Douglas F.
A1 Krause, James E.
A1 Rothman, Steven M.
YR 1997
UL http://molpharm.aspetjournals.org/content/52/1/114.abstract
AB The γ-aminobutyric acid-A (GABAA) receptor complex is allosterically modulated by a variety of substances, some of clinical importance. Barbiturates and neurosteroids augment GABA-currents and also directly gate the channel. A variety of γ-butyrolactone analogues also modulate GABA-induced currents, with some potentiating and others inhibiting. Because several γ-thiobutyrolactone analogues have biphasic effects on GABA currents, experiments with wild-type and picrotoxinin-insensitive GABAA receptors were performed to analyze whether some γ-thiobutyrolactones interact with two distinguishable sites on the GABAA receptor. β-Ethyl-β-methyl-γ-thiobutyrolactone inhibited GABA-induced currents at low concentrations (0.001–1 mm), but potentiated GABA-induced currents at higher concentrations (3–10 mm) in wild-type α1β2γ2-subunit containing ionophores. The related α-ethyl-α-methyl-γ-thiobutyrolactone potentiated submaximal GABA currents in wild-type receptors at both low and high concentrations (0.1–10 mm). Mutations in the second transmembrane domain of α1, β2, or γ2 conferred picrotoxinin-insensitivity onto GABAA receptor complexes. When these mutated α1, β2, or γ2 subunits were incorporated into the receptor complex, β-ethyl-β-methyl-γ-thiobutyrolactone potentiated GABA currents over the entire concentration range (0.1–10 mm). Neither the potentiating activity nor the EC50 of α-ethyl-α-methyl-γ-thiobutyrolactone changed in the mutant receptors. Further studies demonstrated that the mutations did not affect the EC50 of chlordiazepoxide or phenobarbital. These and our earlier results identify a modulatory site on the GABAA receptor distinct from that interacting with barbiturates, benzodiazepines, and steroids. Additionally, they show that the γ-butyrolactones probably interact at two different sites on the ionophore to produce opposite effects on GABA-mediated current.