Differential expression of voltage-gated Ca2+ conductances in human neuroblastoma NB69 cells cultured in defined serum-free and astrocyte-conditioned media.

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) and in "astroglial-conditioned" media (CM). Cells expressed the microtubule associated protein 1A when plated in both media, indicating neuronlike differentiation. Cells of similar sizes and shapes were selected for recordings. Different sets of voltage-gated Ca2+ current types were usually expressed in DM- and CM-plated cells. DM-plated cells exhibited a high-voltage-activated current (HVAC) in isolation, whereas 43% of the CM-plated cells also displayed the low-voltage-activated current (LVAC). The membrane surface density of the HVAC was about twofold higher in CM than in DM-plated cells and increased with plating time from 10 and 16pA/pF (days 1-4) to 24 and 37 pA/pF (days 5-10) in DM- and CM-plated cells, respectively. However, the amplitude of the LVAC did not change significantly with culture age. In conclusion, NB69 cells expressed HVAC in isolation when plated in DM, whereas both HVAC and LVAC were present in many CM-plated cells, suggesting that the CM contained diffusible factors secreted by astroglial cells which: (1) could induce the appearance of the LVAC and (2) increased HVAC current expression.