To explore whether iN cells have functional membrane properties similar to neurons, we performed patch-clamp recordings of TauEGFP-positive cells on days 8, 12, and 20 after infection. Action potentials could be elicited by depolarizing the membrane in current clamp mode the majority of the iN cells analyzed (85.1%, n=47) (Fig. 1k–l). Six cells (14.2%, n=42) exhibited spontaneous action potentials, some as early as eight days after transduction (Fig. 1m). These action potentials could be blocked by tetradotoxin (TTX), a specific inhibitor of Na+ ion channels (Supplementary Fig. 3e). Moreover, in voltage-clamp mode we observed both fast, inactivating inward and outward currents, which likely correspond to opening of voltage-dependent K+- and Na+-channels, respectively, with a possible contribution of Ca2+-channels to the whole cell currents (Fig. 1l, Supplementary Fig. 3f). The resting membrane potentials (RMP) ranged between −30 and −69 mV with an average of ~−55 mV on day 20 (n=12, Fig. 3c, Supplementary Table 2,3). Additionally, we asked whether these cells possessed functional ligand-gated ion channels. iN cells responded to exogenous application of GABA, and this response could be blocked by
