GABA and flunitrazepam binding to neuroblastoma cell membranes--effects of growth conditions, ethanol and pentobarbital.
Strain N2a neuroblastoma cells were grown in monolayer and in spinner culture in Coon's modified Hamms F12 medium, or in Dulbecco's modified Eagle Medium with either high (4.5 g/l) or low (1.0 g/l) glucose, and the specific binding of [3H]GABA and [3H]flunitrazepam were determined. GABA binding was highest in monolayer cells grown in low glucose Dulbecco's, and undetectable in monolayer or spinner cells grown in high glucose Dulbecco's. Binding of flunitrazepam was not sensitive to the medium or culture conditions. Flunitrazepam binding suggested the presence of a 'peripheral' benzodiazepine receptor, because: (a) binding was blocked by RO5-4864 but not clonazepam; (b) binding was not enhanced by 0.1 mM GABA or 50 mM Cl-; and (c) the Kd value was approximately 300 nM. Neither ethanol (100 mM) nor pentobarbital (0.2 mM) had any effect on the binding of GABA; flunitrazepam binding was not affected by ethanol but was decreased about 20% by pentobarbital. GABA, muscimol and veratridine did not alter the membrane potential of the cells, as measured by tetraphenylphosphonium accumulation. The data are discussed in terms of separate receptors for GABA and for benzodiazepines which are not incorporated into a GABA--benzodiazepine receptor--chloride ionophore complex.
D014151:Anti-Anxiety Agents / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D002460:Cell Line; D003470:Culture Media; D046508:Culture Techniques; D000431:Ethanol / Q000494:pharmacology*; D005445:Flunitrazepam / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009447:Neuroblastoma / Q000378:metabolism*; D010424:Pentobarbital / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D014151:Anti-Anxiety Agents; D003470:Culture Media; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D000431:Ethanol; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D010424:Pentobarbital