Non-typical K(+)-current in cesium-loaded guinea pig type I vestibular hair cell

Isolated guinea pig type I vestibular hair cells were voltage clamped at HP-110 mV in whole cell clamp configuration and depolarized up to +20 mV. Increasing depolarizations elicited large outward currents. These currents were replaced, in cesium-loaded cells, by inward/outward currents that reversed at membrane potentials between -55 and -30 mV. The reversal potential varied from cell to cell, and appeared to depend on the intracellular potassium cesium ratio. The current remaining in the presence of intracellular cesium was essentially due to a non-typical potassium conductance, which decreased in the presence of 4-AP and was blocked by 4-AP plus TEA. This current appeared as soon as the membrane was depolarized, showing the high potassium permeability of type I vestibular hair cells. A small part of this current was a strictly calcium inward current, sensitive to flunarizine, with a leakage component in the hyperpolarized state and a voltage component when the cell was depolarized.