Sodium and Potassium Currents of Type I Spiral Ganglion Cells from Rat

Ion channel activity of acutely dissociated type I spiral ganglion cells isolated from rats was investigated using the whole-cell variation of the patch clamp technique. Tetrodotoxin-sensitive sodium current and tetraethylammonium-sensitive potassium current were recorded. With a holding potential of -80 mV, peak sodium currents were generated by depolarizations to membrane potentials more positive than -50 mV. Potassium currents were elicited at membrane potentials more positive than -40 mV. Some cells which did not exhibit sodium current exhibited delayed rectifier potassium currents. Steady-state sodium channel inactivation curve yielded a slope of 12 mV and a half-inactivated potential of -83 mV. Recovery from inactivation of the sodium channel proceeded with a fast and slow time course; recovery began as early as 0.8 ms and proceeded with a time constant of 7.5 ms. It is concluded that type I spiral ganglion cells are endowed with sodium and potassium channels which are responsible for generation and propagation of auditory nerve action potentials.