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

Abstract

During CNS development, changes occur in expression of GABA(A) receptor subunit subtypes and GABA(A) receptor pharmacological and biophysical properties. We used reverse transcription PCR and whole-cell-recording techniques to determine whether GABA(A) 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 alpha5, beta3, gamma3, and pi subtype mRNAs were detected. NT2 GABA(A) receptor currents had a maximal amplitude of 52 pA and an EC(50) of 4.0 microM, 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 GABA(A) receptor subtype mRNAs were detected. Maximal peak whole-cell currents were approximately 50-fold larger than NT2 cell currents, and the GABA EC(50) was higher (39.7 microM). In 13 week NT2-N cells, diazepam, zolpidem, loreclezole, and lanthanum had only small effects on GABA(A) receptor currents, and the zinc IC(50) 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 EC(50,) and zinc IC(50) but that currents were robustly enhanced by diazepam, zolpidem, and loreclezole. During differentiation of NT2 cells to NT2-N cells, GABA(A) receptors underwent changes in subunit expression and pharmacology that were similar to many of the developmental changes in GABA(A) receptors that occur in CNS neurons.