Differential expression of outer hair cell potassium currents in the isolated cochlea of the guinea-pig.

1. Whole-cell currents were recorded from outer hair cells (OHCs) in undissociated tissues from the organ of Corti. The experiments allowed ionic currents to be measured in cells with precise localization on the three most apical cochlear turns. 2. Two major potassium currents were expressed in the cells. One current, named IK, was half-activated at -24 mV and was most prominent in the most apical turn, turn 4. A second, named IK.n, was half-activated at -92 mV and was the major contributor to the current-voltage (I-V) curve of cells from the more basal turns, turns 3 and 2, of the cochlea. 3. IK was specifically blocked by 100 microM 4-aminopyridine (4-AP). In contrast, IK.n was reduced by 5 mM external barium. Superfusion with zero calcium produced no effect on currents in the range from -60 to 0 mV, but reduced currents by a maximum of 15% outside this range. 4. The cell input conductance increased systematically from 3.4 nS in turn 4 to 40 nS in turn 2 measured at a holding potential of -70 mV. 5. The mean leak conductance, measured from the slope of the I-V curve at -110 mV, decreased systematically from 5.2 nS in turn 2, to 2.9 nS in turn 3 and 2.2 nS in turn 4. 6. These data show that hair cell properties can be determined in undissociated cells and are likely to provide a good estimate of the properties of the cells in the intact cochlea. Differences with the properties of isolated OHCs are discussed.