VOLTAGE-DEPENDENT POTASSIUM CURRENTS IN COCHLEAR HAIR-CELLS OF THE EMBRYONIC CHICK

1. Hair cells were isolated from apical and basal regions of the embry onic chick's cochlea. Outward potassium currents were recorded using w hole cell tight-seal voltage clamp. 2. Outward currents in basal hair cells activated and inactivated rapidly. The average time to half-maxi mum at 0 mV was 2.9 ms. The time constant of inactivation at 0 mV was 71 ms. Boltzmann fits to conductance-voltage curves gave an average ha lf-activation voltage of -36 mV, and steady-state inactivation was hal f-maximal at -62 mV. 3. Potassium currents in apical hair cells had sl ower kinetics, with a time to half-maximum of 6.7 ms and an inactivati on time constant of 242 ms at +10 mV. The half-activation voltage deri ved from Boltzmann fits was -16 mV and that for inactivation was -43 m V. 4. With respect to kinetic and voltage-dependent properties, the ra pidly and slowly activating potassium currents of embryonic cells were similar to the rapidly inactivating ''A'' current of mature short hai r cells and to the delayed rectifier of mature tall hair cells. Howeve r, unlike the adult currents, the embryonic currents did not show diff erential sensitivities to tetraethylammonium chloride and 4-aminopyrid ine. As early as the tenth day of embryogenesis, hair cells at the api cal and basal extremes of the cochlea produced functionally distinct v oltage-gated potassium currents.