An electrophysiological comparison of solitary type I and type II vestibular hair cells.

We have studied the electrophysiological properties of enzymatically dissociated adult pigeon semicircular canal type I (chalice shaped) and type II (cylindrical shaped) hair cells using whole cell patch clamp techniques. Under current clamp conditions, type I hair cells often exhibit more hyperpolarized resting potentials than type II hair cells, and type I hair cells also have higher input conductances (measured with negative current steps) than type II hair cells. Under voltage clamp conditions, type I hair cells showed large, persistent outward currents over the range of about -70 to -50 mV, whereas, type II hair cells showed little or no current over this potential range. The persistent outward current of type I hair cells was not inactivated at a holding potential of -30mV, a potential that inactivated the rapidly inactivating, IA, and delayed rectifier, IK, currents of type II hair cells. This current probably contributes to both the resting potential and input conductance of type I hair cells.