Figure 6.

Protons released during exocytosis cause a transient block of Ca²⁺ currents. A, The hair cell was depolarized from −60 to −30 mV for 500 ms in control condition (black) and after perfusion of external solution including 40 mm HEPES (blue). B, External solution of pH 8.9 with 10 mm TABS increased the amplitude of Ca²⁺ currents and the ΔC_m jump, but inhibited the transient block of Ca²⁺ currents. Initial kinetics of the Ca²⁺ currents in B1 are shown in an expanded time scale in B2. As a pH 8.9 solution was applied, the transient block of Ca²⁺ currents was quickly removed. The time lapsed after a control recording as the pH 8.9 solution was being perfused is shown in different colors. In B3, we quantify the effects of the external solution with pH 8.9. The amplitudes of Ca²⁺ currents (left) and ΔC_m (right) evoked by a 500-ms-long depolarization from −60 to −30 mV are compared in control (black) and after >3–5 min of perfusion with the pH 8.9 solution (purple). The average amplitude of Ca²⁺ currents was significantly increased from 262 ± 22 to 383 ± 20 pA (n = 6) and ΔC_m was significantly enhanced from 174 ± 26 to 271 ± 39 fF (n = 6) by pH 8.9 external solution. *p < 0.05, paired t test; ***p = 0.001, paired t test. Open circles indicate individual pairs.