The human neuroblastoma cell line, IMR-32 possesses a GABAA receptor lacking the benzodiazepine modulatory site.
GABAA receptors were identified in IMR-32 cell membranes by the binding of [35S]t-butyl-bicyclophosphorothionate ([35S]TBPS) to the chloride channel. GABA (IC50 2.2 microM), muscimol (IC50 0.8 microM), picrotoxin (IC50 1.7 microM), pentobarbitone (IC50 108 microM), etomidate (IC50 53 microM), chlormethiazole (IC50 98 microM) and Ro 5-3663 (IC50 280 microM) all inhibited [35S]TBPS binding. The potency of these drugs at the [35S]TBPS binding site in IMR-32 cell membranes did not correlate with their potency on [35S]TBPS binding to rat cortical membranes (linear correlation of pIC50 values, r = 0.75, NS). No specific binding of the benzodiazepine ligands [3H]flunitrazepam or [3H]Ro 15-4513 to IMR-32 cell membranes was observed. Chloride efflux from IMR-32 cells was studied using the fluorescent dye 6-methoxy-N-(3-sulphopropyl) quinolinium. Chloride efflux was stimulated by GABA and muscimol (0.1-100 microM) but not by the GABAB agonist baclofen (100 microM). In the absence of exogenous GABA chloride efflux was stimulated by chlormethiazole (1-100 microM) in a picrotoxin-sensitive manner. Flurazepam (1-100 microM) both alone and in the presence of GABA had no effect on chloride efflux. It is concluded that IMR-32 cells contain a functional GABAA receptor which differs from that in rat cortex both in its general pharmacology and specifically in the absence of the allosteric modulatory site sensitive to benzodiazepines.
Anderson
S M
SM
Astra Neuroscience Research Unit, London, U.K.
De Souza
R J
RJ
Cross
A J
AJ
D000818:Animals; D001386:Azides / Q000378:metabolism; D001569:Benzodiazepines / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels; D005445:Flunitrazepam / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D001386:Azides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D018118:Chloride Channels; D008565:Membrane Proteins; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D005445:Flunitrazepam; C037476:tert-butylbicyclophosphorothionate; C042957:Ro 15-4513