We have characterized the profile of membrane currents in an immortalized human neural stem cell line, HB1.F3 cells, using whole-cell patch clamp technique. Human neural stem cell line generated from primary cell cultures of embryonic human telencephalon using a replication-incompetent retroviral vector containing v-myc expresses nestin, a cell type-specific marker for neural stem cells. The human neural stem cells expressed both outward and inward K(+) currents with no evidence for Na(+) currents. The density of the outward, delayed rectifying type K(+) current was 1.8 +/- 0.015 nA/pF, and that of the inwardly rectifying K(+) current was 0.37 +/- 0.012 nA/pF (at 30 mM of [K(+)](o)). In order to induce neuronal differentiation of the neural stem cells, a full-length coding region of NeuroD, a neurogenic transcription factor, was transfected into HB1.F3 cells. Introduction of NeuroD induced expression of Na(+) currents with the current density of 0.042 +/- 0.011 nA/pF. The presence of two types of K(+) currents and expression of Na(+) currents induced by NeuroD appear to reflect the characteristic physiological features of human neural stem cells.