Figure 1.

TTX-sensitive transient and persistent Na⁺ currents identified in SGNs cultured from hearing mice. A, Current responses recorded using K⁺-filled patch electrodes, from a representative rapidly-adapting P14 SGN during 200-ms voltage steps. A transient inward Na⁺ current (I_NaT) was followed by LVA and HVA outward K⁺ currents. B, Current response from the same cell during a voltage ramp (between −143 and +47 mV, duration 400 ms) before (control) and after bath application of 100 nM DTX-K. DTX-K blocked the LVA K⁺ current, revealing a small inward current activated at potentials positive to −65 mV (detailed in the inset). C, Current responses recorded using K⁺-filled patch electrodes, from a representative nonadapting P14 SGN during 200-ms voltage steps (protocol described in A). Activation of I_NaT was followed by activation of HVA K⁺ currents. LVA K⁺ currents were absent from this cell. D, Current responses from the same SGN, during a voltage ramp before (control) and after bath application of 100 nM TTX. A TTX-sensitive inward current activated at potentials positive to −65 mV (difference current, detailed in the inset). E, TTX-subtracted currents recorded from the SGN in D, during 200-ms depolarizing voltage steps. A voltage step to −53 mV activated a small persistent inward current (I_NaP), whereas the voltage step to −33 mV activated a large I_NaT (*, peak current cropped for clarity) and a small I_NaP. F, Comparison of the voltage dependence of TTX-sensitive I_NaT and I_NaP (measured at the arrow in E) in this SGN.