Fig. 3.

MET current adaptation in mouse cochlear hair cells is removed by high intracellular BAPTA. (A and B) MET currents recorded from an OHC (A) and an IHC (B) in response to a 50-Hz sinusoidal force stimuli to the hair bundles at the membrane potential of −81 mV in the presence of different intracellular BAPTA concentrations. Recordings are as in Fig. 1 A and B. Note the increased resting MET current (difference between dashed lines and arrows) with increasing BAPTA concentration. (C) Resting open probability of the MET current recorded in OHCs and IHCs obtained at −81 mV and using different concentrations of intracellular BAPTA. (D) Step driver voltages to the fluid jet (Top) and MET currents recorded from OHCs (Left) and IHCs (Right) at −81 mV (Bottom) and +99 mV (Middle) in the presence of 0.1 mM BAPTA. Note that all manifestations of MET current adaptation were removed at +99 mV as shown in Fig. 1 D and E with 1 mM EGTA. (E) MET currents recorded from OHCs (Middle) and IHCs (Bottom) at −81 mV in the presence of 5 mM BAPTA. (F) MET currents recorded from an OHC at −81 and +99 mV in the presence of 10 mM BAPTA. As for 5 mM BAPTA (E), MET current adaptation was absent. (G) Normalized peak MET current recorded from OHCs at the holding potential of −81 and +99 mV as a function of bundle displacement in the presence of 5 mM (n = 6; Left) and 10 mM (n = 6; Right) intracellular BAPTA. Similar to the experiments in low Ca²⁺ (Fig. 2E), little (5 mM) or no (10 mM) leftward shift in the MET current-displacement relation was observed when cells were held at +99 mV in the presence of intracellular BAPTA. Resting open probability between −81 mV (5 mM: 0.39 ± 0.02, n = 6; 10 mM: 0.43 ± 0.04, n = 6) and +99 mV (5 mM: 0.57 ± 0.02; 10 mM: 0.48 ± 0.04) was only significantly different using 5 mM BAPTA (paired t test: P < 0.001).