Allosteric modulation of [35S]TBPS-binding in the cerebral cortex of the rat during postnatal development.
The ontogenesis of the GABA-gated Cl- channel was investigated in the cerebral cortex of the rat by monitoring the binding parameters of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) at intervals after birth (1-90 days). To investigate the influence of the developmental changes in the content of GABA on [35S]TBPS-binding, the assays were carried out in unwashed membranes, in which the concentration of GABA was dependent on its content in vivo, and in repeatedly washed membranes in the presence of defined concentrations of exogenous GABA. At birth, the density (Bmax) of [35S]TBPS-binding sites in unwashed membranes was similar to that found in well-washed membranes. However, in unwashed membranes, the number of [35S]TBPS-binding sites increased by two-fold within 10 days after birth whereas in washed membranes it increased by four-fold during the same period. The higher density of [35S]TBPS-binding sites in washed membranes as compared with the unwashed counterparts persisted throughout development. In unwashed membranes, the apparent Kd for [35S]TBPS-binding increased with age whereas in washed membranes the affinity of [35S]TBPS for its binding sites remained constant throughout development. The binding of [35S]TBPS to the GABA-gated Cl- channel is allosterically modulated by drugs acting on different sites of the GABAA receptor complex. Thus, GABA and diazepam decrease [35S]TBPS-binding whereas the GABAA receptor antagonist, bicuculline, and the inverse agonist for benzodiazepine receptors, 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid methyl ester, increase it.(ABSTRACT TRUNCATED AT 250 WORDS)
Giorgi
O
O
Department of Toxicology, University of Cagliari, Italy.
Cancedda
E
E
Lecca
D
D
Orlandi
M
M
Corda
M G
MG
D000375:Aging / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000493:pharmacokinetics*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002540:Cerebral Cortex / Q000254:growth & development* / Q000378:metabolism*; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D003292:Convulsants / Q000493:pharmacokinetics*; D003975:Diazepam / Q000494:pharmacology; D005445:Flunitrazepam / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism; D013237:Stereoisomerism; D013462:Sulfur Radioisotopes; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D018118:Chloride Channels; D003292:Convulsants; D011963:Receptors, GABA-A; D013462:Sulfur Radioisotopes; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; C037476:tert-butylbicyclophosphorothionate; D003975:Diazepam; D001640:Bicuculline