DIFFERENTIAL EXPRESSION OF VOLTAGE-GATED CA2-FREE AND ASTROCYTE-CONDITIONED MEDIA( CONDUCTANCES IN HUMAN NEUROBLASTOMA NB69 CELLS CULTURED IN DEFINED SERUM)

Voltage-gated Ca2+ conductances were investigated with the whole-cell patch-clamp technique-either using Ca2+ or Ba2+ as charge carriers-in NB69 human neuroblastoma cells plated in ''defined'' serum-free (DM) a nd in ''astroglial-conditioned'' media (CM). Cells expressed the micro tubule associated protein 1A when plated in both media, indicating neu ronlike differentiation. Cells of similar sizes and shapes were select ed for recordings. Different sets of voltage-gated Ca2+ current types were usually expressed in DM- and CM-plated cells. DM-plated cells exh ibited a high-voltage-activated current (HVAC) in isolation, whereas 4 3% of the CM-plated cells also displayed the low-voltage-activated cur rent (LVAC). The membrane surface density of the HVAC was about twofol d higher in CM than in DM-plated cells and increased with plating time from 10 and 16pA/pF (days 1-4) to 24 and 37pA/pF (days 5-10) in DM- a nd CM-plated cells, respectively. However, the amplitude of the LVAC d id not change significantly with culture age. In conclusion, NB69 cell s expressed HVAC in isolation when plated in DM, whereas both HVAC and LVAC were present in many CM-plated cells, suggesting that the CM con tained diffusible factors secreted by astroglial cells which: (I) coul d induce the appearance of the LVAC and (2) increased HVAC current exp ression. (C) 1997 Wiley-Liss, Inc.