BASIC FGF-RESPONSIVE TELENCEPHALIC PRECURSOR CELLS EXPRESS FUNCTIONALGABA(A) RECEPTOR CL- CHANNELS IN-VITRO

We have previously described the expression of specific gamma-aminobut yric acid (GABA)(A) receptor subunits and their transcripts in the cor tical neuroepithelium (Ma and Barker, 1995, 1998), However, it is not clear whether neural precursor cells exposed to basic fibroblast growt h factor (bFGF) in vitro reproduce the biological properties of neuroe pithelial cells in vivo within the embryonic ventricular zone. In the present study, neural precursor cells were isolated from the telenceph alic neuroepithelium of embryonic day 13-13.5 rats and exposed to bFGF in serum-free medium. Basic FGF-responsive cells were capable of divi ding and differentiating into neurons and astrocytes, The rapidly divi ding cells formed multicellular spheres and then a rosette-like format ion in which a majority of cells expressed GABA(A) receptor alpha 4, b eta 1, or gamma 1 subunit proteins. We found in perforated patch-clamp recordings that GABA depolarized bromodeoxyundine (BrdU)(+) precursor cells, and under voltage-clamp induced a bicuculline-sensitive curren t that reversed at the Cl- equilibrium potential, GABA also increased cytoplasmic Ca2+ in a significant number of BrdU(+) cells that was blo cked by bicuculline, The bicuculline sensitivity of these pharmacologi cal effects implicates GABA(A) receptor/ Cl- channels, since bicuculli ne is a competitive GABA(A) antagonist at these channels in well-diffe rentiated cells. It is possible that the three GABA(A) receptor subuni ts (alpha 4, beta 1, and gamma 1) found in precursor cells form the Cl - channels detected electrophysiologically. The functional GABAA recep tor/Cl- channels and associated regulation of their cytoplasmic Ca2+ l evels via bicuculline-sensitive mechanisms may play significant roles in the regulation of neural cell proliferation in this model neuroepit helium. (C) 1998 John Wiley & Sons, Inc.