Membrane properties of irNCs. (A) Membrane properties of four-factor irNCs. Single, action potential-like responses were recorded following current injections between −10 and 40 pA, in 10 pA steps. (B) Typical action potentials recorded in the five-factor group. The five-factor group of mature irNCs under the depolarization current released action potentials. (C) In the voltage-clamp recording, an inward current was induced by voltage stimulation, with the membrane potential held at −50 mV and voltage steps between −70 and 30 mV, which was inhibited by TTX. (D) A gap remained between the action potential amplitude and frequency between the five-factor group and embryonic stem cell-derived neurons. irNCs, induced resembled neuronal cells; TTX, tetrodotoxin.