Outer hair cells were recorded under voltage clamp configuration with electrodes pulled from borosilicate glass capillaries (GC150TF-10 Clark Electromedical, UK), on a Sachs-Flaming horizontal electrode puller (Sutter Instruments, USA). Recording electrodes were back filled with one of the following internal solutions. Solution 1 (mM): KCl 136, KOH 28, MgCl2 1.5, CaCl2 0.1, EGTA 11, Hepes 5; solution 2 (mM): CsCl 100, KCl 50, KOH 3.5, NaCl 2, MgCl2 2, EGTA 1.1, Hepes 5, glucose 4; solution 3 (mM): KCl 100, KOH 39, NaCl 5.8, MgCl2 2, CaCl2 0.1, BAPTA 10, Hepes 5, glucose 47. All solutions were adjusted to pH 7.20 and to 300 mosmol (kg H2O)−1. Electrode resistance ranged from 3 to 6 MΩ. Patch clamp recordings were performed as previously described in detail (Blanchet et al. 1996) by means of either an Axopatch-1D amplifier (Axon Instruments, Foster City, CA, USA) or a Biologic RK-400 amplifier (Biologic Science Instruments, France). Axotape and pCLAMP software (Axon Instruments) were used for data collection and analysis. Electrode capacitance was compensated as much as possible and series resistance was compensated at 80 %. Voltage errors attributable to residual uncompensated series resistance (less than 5 mV in all recordings) were not corrected for, but those due to liquid junction potentials were corrected for during data analysis (Blanchet et al. 1996). All experiments were performed at room temperature (20-22°C).