GABAAReceptor Pharmacology and Subtype mRNA Expression in Human Neuronal NT2-N Cells

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Abstract
Human NT2 teratocarcinoma cells differentiate into neuron-like NT2-N cells when treated with retinoic acid. GABA evoked concentration-dependent whole-cell currents in NT2-N cells with an EC50of 21.8 μmand a Hill slope of 1.2. GABAAreceptor (GABAR) currents reversed atECl−and did not display voltage-dependent rectification. GABAR single channels opened in bursts to a 23 pS main conductance level and a 19 pS subconductance level, with infrequent openings to a 27 pS conductance level. Kinetic properties of the main conductance level were similar to other native and recombinant GABAR channels. Diazepam and zolpidem enhanced GABAR currents with moderate affinity, whereas methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate inhibited GABAR currents. Loreclezole enhanced GABAR currents with high affinity, but furosemide antagonized GABAR currents with low affinity. The neurosteroids alphaxalone and pregnenolone sulfate appropriately modulated GABAR currents. Zinc blocked GABAR currents with low affinity, but lanthanum did not significantly alter NT2-N GABAR currents. Reverse transcription PCR (RT-PCR) performed on RNA from NT2-N cells clearly detected transcripts encoding human α2, α3, α5, β3, γ3, and π subtypes. The combined pharmacological and RT-PCR results are most consistent with a single or predominant GABAR isoform composed of an α2 and/or α3 subtype combined with the β3 and γ3 subtypes. The data do not rule out receptors containing combinations of α2 and/or α3 subtypes with the α5 subtype or receptors with both β1 and β3 subtypes. The presence or absence or the π subunit in functionally expressed receptors could not be determined.