Fig. 5.

Ionophore-mediated elevation of intracellular free Ca²⁺ concentration increases the OHC resting length, enhances electromotile responses, but does not affect nonlinear capacitance. A, Fluorescent image of an OHC filled with Oregon Green 488 BAPTA-1 (50 μm) through the patch pipette. B, The same cell shown in A 1 min after the application of 25 μm ionomycin. Scale bar, 10 μm. C, Time course of fluorescence changes (top), resting length (middle), and whole-cell current (bottom) after application of ionomycin to the cell shown in A and B. Fluorescence intensity was computed by averaging pixel values throughout the cell body. Deflections on the current and length records are caused by the delivery of triangular voltage ramps (numbered 1–4) to the cell. A closedhorizontalbar at thebottom of the panel indicates the timing of the drug application. D, Membrane capacitance–voltageC_m(V) relationships before (control; ramp 1; closed squares) and after (ramps 2, 3, 4;open symbols) application of ionomycin, obtained during the correspondingly numbered voltage ramps in C. Data were fitted by the scaled derivatives of the Boltzmann function. E, Electromotility responses of a different OHC before application of ionomycin (Control;closed squares) and after recovery from ionomycin-induced turgor loss (Ionomycin, open circles; 2 min after drug application). Data were fitted by Boltzmann functions. Inset, A sample of the current–voltage relationship of the ionomycin-sensitive fraction of the whole-cell current.