Figure 5.

Ca²⁺ sensitivity of multiquantal EPSCs. A, EPSCs were recorded from a voltage-clamped afferent fiber, while a connected hair cell dialyzed with 2 mm EGTA was depolarized for 10 s from a holding potential of −90 mV to each of the indicated membrane potentials. The majority of the EPSCs recorded at the most negative potentials were small and putatively uniquantal, but depolarization progressively increased the proportion of large and presumably multiquantal events. B, Averaged EPSCs from the same fiber with the hair cell held at the membrane potentials indicated. The numbers in brackets indicate the number of EPSCs averaged at each hair cell membrane potential. The frequency and average amplitude of the EPSCs increased as the hair cell was depolarized more strongly. C, EPSCs were recorded from another afferent fiber, while a connected hair cell dialyzed with 10 mm BAPTA was stepped for 10 s from a holding potential of −90 mV to each of the indicated potentials. The presence of a fast Ca²⁺ buffer shifted the voltage dependence by ∼10 mV with respect to that in A. The records were obtained 3.5 min after the inception of the whole-cell recording from the hair cell.