Characterization of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding to GABAA receptors in postmortem human brain.
OBJECTIVE
The aim of the present study was to determine whether binding of [(35)S]t-butylbicyclophosphorothionate ([(35)S]TBPS) to the convulsant binding site of GABA(A) receptors in human postmortem brain samples can be used as an in vitro index of the functional activation of these receptors.


METHODS
Postmortem stability of [(35)S]TBPS binding was assessed in rat brain samples harvested at various times after death and the binding properties of [(35)S]TBPS binding (K(D) and B(max)) were determined in human postmortem brain using radioligand binding studies. In addition, the ability of human brain [(35)S]TBPS binding to be allosterically modulated by compounds that bind at recognition sites distinct from the convulsant binding site was measured.


RESULTS
Whereas binding of [(3)H]Ro 15-1788 to the benzodiazepine binding site and [(3)H]muscimol to the agonist (GABA) binding site were retained over a 20 h postmortem interval, there was a significant decrease in the affinity and number of [(35)S]TBPS binding sites. Nevertheless, [(35)S]TBPS binding in human brain could be inhibited by TBPS, picrotoxin, loreclezole and pentobarbital and modulated by GABA with potencies comparable to those observed in rats. In addition, the GABA-induced reduction in human brain [(35)S]TBPS binding could be modulated by benzodiazepine site ligands in a manner that reflected their intrinsic efficacies.


CONCLUSIONS
These results suggest that allosteric coupling between the [(35)S]TBPS, GABA and benzodiazepine binding sites is preserved in postmortem human brain and that [(35)S]TBPS binding in this tissue may be used to study functional characteristics of native human GABA(A) receptors.
Atack
J R
JR
Neuroscience Research Centre, Merck Sharp and Dohme Research Laboratories, Terlings Park, Eastwick Road, Harlow, Essex, UK. JAtack@prdus.jnj.com
Ohashi
Y
Y
McKernan
R M
RM
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism*; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D003292:Convulsants / Q000378:metabolism*; D018756:GABA Antagonists / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*; D013462:Sulfur Radioisotopes / Q000378:metabolism; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D019086:Bridged Bicyclo Compounds, Heterocyclic; D003292:Convulsants; D018756:GABA Antagonists; D008024:Ligands; D011963:Receptors, GABA-A; D013462:Sulfur Radioisotopes; D005680:gamma-Aminobutyric Acid; C037476:tert-butylbicyclophosphorothionate