Alterations in membrane excitability of NG108-15 cells induced by differentiation. A: Representative traces show the membrane potential response to a depolarizing current injection (100 pA, 1 sec) under whole-cell current-clamp configuration. B: Action potential (AP) frequency in undifferentiated (day0) and differentiated NG108-15 cells. TTX: tetrodotoxin. Data are means ± SEM, n is the number of cells.