Cyclothiazide binding to the GABAA receptor.
In order to explore the molecular interaction between cyclothiazide (CTZ) and gamma-aminobutyric acidA (GABAA) receptors, possibly underlying inhibition of GABAA receptor currents, [3H]-CTZ was synthesized. Binding of [3H]-CTZ to rat brain synaptic membranes could be observed only in the presence of the GABAA receptor antagonist (-)[1S,9R]-bicuculline methiodide (BMI) (EC(50,BMI)=500+/-80microM). GABA decreased [(3)H]-CTZ binding induced by the presence 300microM and 3mM BMI with IC(50,GABA) values of 300+/-50microM and 5.0+/-0.7mM, respectively. Binding of CTZ to [3H]-CTZ labeled sites was characterized by IC(50,CTZ) values of 0.16+/-0.03muM ([BMI]=300microM) and 7.0+/-0.5microM ([BMI]=3mM). Binding of the diastereomeric fraction [3H]-(3R,1'S,4'S,5'R+3S,1'R,4'R,5'S)-CTZ induced by 3mM BMI was quantitatively the more significant in cerebrocortical and hippocampal membranes. It was characterized by IC(50,CTZ)=80+/-15nM and IC(50,GABA)=13+/-3mcapital EM, Cyrillic. In the absence of BMI, CTZ (1mM) significantly decreased GABA-induced enhancement of [3H]-flunitrazepam binding. Our findings suggest that functional inhibition may occur through binding of CTZ to an allosteric site of GABAA receptors. This allosteric site is possibly emerged in the receptor conformation, stabilized by BMI binding.
Szárics
Eva
E
Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary. szeva@chemres.hu
Simon
Agnes
A
Visy
Júlia
J
Simon-Trompler
Edit
E
Banka
Zoltán
Z
Héja
László
L
Hársing
László Gábor
LG
Blaskó
Gábor
G
Kardos
Julianna
J
D000818:Animals; D001581:Benzothiadiazines / Q000737:chemistry / Q000494:pharmacology*; D001921:Brain / Q000166:cytology; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000648:ultrastructure; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium / Q000493:pharmacokinetics; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics
D001581:Benzothiadiazines; D018691:Excitatory Amino Acid Antagonists; D011963:Receptors, GABA-A; D014316:Tritium; D005680:gamma-Aminobutyric Acid; C004639:cyclothiazide