EFFECTS OF LIPOPHILIC IONS ON OUTER HAIR CELL-MEMBRANE CAPACITANCE AND MOTILITY

The outer hair cell (OHC) from the mammalian organ of Corti possesses a bell-shaped voltage-dependent capacitance function. The nonlinear ca pacitance reflects the activity of membrane bound voltage sensors asso ciated with membrane motors that control OHC length. We have studied t he effects of the lipo philic ions, tetraphenylborate (TPB+) and tetra phenylphosphonium (TPP+), on nonlinear capacitance and motility of iso lated guinea-pig OHCs. Effects on supporting cells were also investiga ted. TPB- produced an increase in the peak capacitance (Cm-pk) and shi fted the voltage at peak capacitance (V-pkCm) to hyperpolarized levels . Washout reversed the effects. Perfusion of 0.4 mu M TPB- caused an a verage increase in Cm-pk of 16.3 pF and V-pkCm shift of 13.6 mV. TPP+, on the other hand, only shifted V-pkCm in the positive direction, wit h no change in Cm-pk. The contributions from native OHC and TPB--induc ed capacitance were dissected by a double Boltzmann fitting paradigm, and by blocking native OHC capacitance. While mechanical response stud ies indicate little effect of TPB- on the motility of OHCs which were in normal condition or treated with salicylate or gadolinium, the volt age at maximum mechanical gain (V-delta Lmax) was shifted in correspon dence with native V-pkCm, and both changed in a concentration-dependen t manner. Both TPB--induced changes in Cm-pk and V-pkCm were affected by voltage prepulses and intracellular turgor pressure. TPB- induced a voltage-dependent capacitance in supporting cells whose characteristi cs were similar to those of the OHC, but no indication of mechanical r esponses was noted. Our results indicate that OHC mechanical responses are not simply related to quantity of nonspecific nonlinear charge mo ved within the membrane, but to the effects of motility sensor charge movement functionally coupled to a mechanical effector.