Ionic currents in isolated vestibular hair cells from the guinea-pig crista ampullaris

Ionic currents have been recorded under whole cell patch clamp in cells isolated from the guinea-pig vestibular system. Type I and type II cells were separately identified. Type II cells were further classified as short (less than 15 microns in length) or tall (greater than 15 microns). Under whole cell voltage clamp, cells showed an outward current which activated at potentials above about -50 mV, and tail currents which reversed near the potassium equilibrium potential. The outward current was reduced in the presence of external 10 mM tetraethylammonium or cadmium ions and when calcium was removed from the external medium. A small cadmium-sensitive transient inward current, a putative calcium current, was observed in cells loaded with caesium from the patch pipette. In 27 out of 64 cells a component of the recorded outward current inactivated. Such current components were most common in tall type II cells. This inactivating component was blocked by 4-aminopyridine and removed by depolarizing prepulses consistent with it being an A-type potassium current. Type I cells, on the other hand, showed mainly a non-inactivating outward current which slowly relaxed on repolarization to resting potentials. When membrane potentials were measured under current clamp, injections of less than 100 pA produced a single, highly damped transient followed by a plateau in Type II cells. No such transient was present in Type I cells. There is thus little evidence for an electrical resonance in these cells.