The human neuroblastoma cell line, IMR-32 possesses a GABAA receptor lacking the benzodiazepine modulatory site

• Published in: Neuropharmacology Vol. 32; no. 5; p. 455
• Main Authors: Anderson, S M, De Souza, R J, Cross, A J
• Format: Journal Article
• Language: English
• Published: England 01-05-1993
• Subjects: Animals; Azides - metabolism; Benzodiazepines - metabolism; Bridged Bicyclo Compounds - metabolism; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane - metabolism; Chloride Channels; Flunitrazepam - metabolism; Humans; Kinetics; Membrane Proteins - metabolism; Neuroblastoma - metabolism; Radioligand Assay; Rats; Receptors, GABA-A - metabolism; Tumor Cells, Cultured
• ISSN: 0028-3908
• DOI: 10.1016/0028-3908(93)90169-4

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.