Figure 5.

Ca²⁺ buffer dependence of paired-pulse ratios. EPSCs were elicited with a pair of 20 ms pulses from −90 to −30 mV (A–C). In A and B, EPSCs were recorded from afferent fibers while the hair cells were depolarized by a pair of 20 ms voltage steps from −90 to −30 mV with various interpulse intervals (3–500 ms). The averaged paired-pulse ratios of EPSC peak amplitudes (EPSC₂/EPSC₁) were fit by exponentials (green and red lines). In D, paired-pulse ratio was calculated from ΔC_m evoked by a pair of 20 ms voltage steps from −90 to −30 mV with interpulse interval of 20, 50, 100, and 200 ms. A, The averaged EPSC₂/EPSC₁ with 2 mm EGTA as an internal calcium buffer in hair cells (black; n = 6–9). EPSC₂/EPSC₁ with interpulse intervals from 3 to 50 ms (3, 5, 10, 15, 20, 30, and 50 ms) increased exponentially (τ₁ = 10.9 ms, green). The red line shows a single exponential fit with a time constant of 39.2 ms. B, The averaged EPSC₂/EPSC₁ with 2 mm BAPTA as an internal calcium buffer in hair cells (blue; n = 4–8). EPSC₂/EPSC₁ values with 3, 20, and 50 ms interpulse intervals were significantly different from those of 2 mm EGTA (p < 0.05). The time constant of a single exponential fit between the 3 ms and 50 ms intervals was 9.8 ms (τ₁; green) and the exponential time constant between 50 ms and 500 ms intervals was 38.3 ms (τ₂; red). C, The averaged paired-pulse ratio of EPSCs (3, 5, 10, 20, 50, 100, and 200 ms interpulse intervals) with 10 mm EGTA internal calcium buffer in the hair cells (green squares; n = 4–9). The averaged paired-pulse ratio with 10 mm EGTA was significantly decreased only for the 50 ms interval compared with 2 mm EGTA (red asterisk, p < 0.05). D, With 10 mm EGTA (green filled circle), ΔC_m²/ΔC_m¹ was not significantly different from 2 mm EGTA (black open square, same data as in with Fig. 4C) except for the data point with 50 ms interval (red asterisk; p < 0.05).