Chronic GABA exposure down-regulates GABA-benzodiazepine receptor-ionophore complex in cultured cerebral cortical neurons.
Cerebral cortical cultured neurons were characterized for GABA-benzodiazepine (BZ) receptor complex, and the effect of chronic exposure of cortical neurons to GABA on GABA-BZ receptor system was investigated. In the intact cells, the [3H]flunitrazepam binding was rapid and saturable, with an apparent Kd of 4.2 +/- 1.5 nM and Bmax of 776 +/- 54 fmol/mg protein. Specifically bound [3H]flunitrazepam was displaced in a concentration-dependent manner by various BZ receptor ligands such as Ro15-1788, DMCM, Ro15-4513, clonazepam, alprazolam, diazepam and zolpidem, and enhanced by GABA, muscimol and pentobarbital. GABA induced enhancement of 36Cl-influx in a concentration-dependent manner (EC50 = 9 +/- 2 microM). Chronic exposure of the cultured neurons to GABA resulted in a reduced [3H]flunitrazepam, [3H]GABA, [3H]Ro15-1788, [3H]Ro15-4513 and [35S]TBPS binding, a reduced enhancement of [3H]flunitrazepam binding by GABA, and a reduced GABA-induced 36Cl-influx susceptible to reversal by concomitant exposure of the cultures to R 5135, a GABAA-receptor antagonist. These findings indicate that cerebral cortical cultured neurons provide an ideal model to study GABA-BZ receptor complex using binding and 36Cl-influx assays, and chronic exposure of cortical cultures to GABA leads to a down-regulation of GABA-BZ receptor system. It is a GABAA receptor-mediated slow process.
Mehta
A K
AK
Department of Pharmacology, University of Texas Health Science Center, San Antonio 78284-7764.
Ticku
M K
MK
D000818:Animals; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects*; D002713:Chlorine; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D007476:Ionophores / Q000737:chemistry*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects*; D011868:Radioisotopes; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000737:chemistry / Q000187:drug effects*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D007476:Ionophores; D011868:Radioisotopes; D011963:Receptors, GABA-A; D002713:Chlorine; D005680:gamma-Aminobutyric Acid