GABAA Receptors Expressed in Undifferentiated Human Teratocarcinoma NT2 Cells Differ from Those Expressed by Differentiated NT2-N Cells

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Abstract
During CNS development, changes occur in expression of GABAA receptor subunit subtypes and GABAAreceptor pharmacological and biophysical properties. We used reverse transcription PCR and whole-cell–recording techniques to determine whether GABAA receptor expression and function also changed during retinoic acid–induced differentiation of human Ntera 2 (NT2) teratocarcinoma cells into neuron-like cells (NT2-N cells). In undifferentiated NT2 cells only α5, β3, γ3, and π subtype mRNAs were detected. NT2 GABAA receptor currents had a maximal amplitude of 52 pA and an EC50 of 4.0 μm, were relatively insensitive to enhancement by zolpidem and diazepam, and were enhanced by loreclezole and inhibited by lanthanum, zinc, and furosemide. In contrast, in NT2-N cells after 13 weeks of retinoic acid treatment, all GABAA receptor subtype mRNAs were detected. Maximal peak whole-cell currents were ∼50-fold larger than NT2 cell currents, and the GABA EC50was higher (39.7 μm). In 13 week NT2-N cells, diazepam, zolpidem, loreclezole, and lanthanum had only small effects on GABAA receptor currents, and the zinc IC50 for current inhibition was significantly higher than that for NT2 cells. In a previous study, we showed that NT2-N cells after 5 weeks of retinoic acid treatment had moderate peak currents, GABA EC50, and zinc IC50 but that currents were robustly enhanced by diazepam, zolpidem, and loreclezole. During differentiation of NT2 cells to NT2-N cells, GABAA receptors underwent changes in subunit expression and pharmacology that were similar to many of the developmental changes in GABAA receptors that occur in CNS neurons.