Neuronal differentiation of human single-cell–derived clones. (A) Na⁺ currents; the tracings were elicited by 80-ms pulses from a holding potential of − 100 mV to test potentials ranging from − 50 to + 40 mV, in 10-mV increments, applied every 10 seconds (protocol in the inset); to the right is represented the corresponding I/V relationship. The potassium currents were blocked by equimolar substitution of intracellular K⁺ with Cs⁺. (B) Delayed rectifier potassium currents obtained using the same activation protocol described in panel A; to the right is the corresponding I/V relationship. Here, as for the recordings shown in panel C, the sodium current was blocked by TTX 1 μM. (C) A-type K⁺ currents; traces obtained with the inactivation protocol shown in the inset: a test potential to − 30 mV was preceded by a 180-ms conditioning step to potentials ranging from − 100 to − 10 mV, and the resulting peak amplitudes are represented to the right as a function of the conditioning potential (○). The peak currents obtained in the same cell with the activation protocol (from − 60 to + 40 mV in 10-mV increments, not shown) are represented to the right (▵). (D) Glutamic acid production. Fluorometric determination of glutamic acid production (expressed in pg and normalized for the seeded cell number) produced between day 10 and day 12 from 10 single-cell–derived clones, either in undifferentiated (▭) or differentiated state (). Results are expressed as mean (± SEM). *P < .01 versus single-cell–derived clones.