Figure 5.

Shape of ribbon synapses and their functional coupling with Ca²⁺ channels. A, B, Typical cross-sectional profiles of synaptic ribbons from an apical and a basal IHC, respectively. Note that the ribbon (filled arrowheads) in the apical IHC (A) had a round cross-sectional profile, whereas that in the basal cell (B) was elongated in shape. Open arrowheads indicate synaptic membrane thickenings. Scale bar, 100 nm. C, D, ΔC_m from apical and basal IHCs, respectively, in response to a 100 ms voltage step (to approximately −11 mV) using different intracellular BAPTA concentrations (indicated next to the traces). E, F, Average ΔC_m to voltage steps from 5 to 100 ms in apical and basal IHCs. G, Average ΔC_m and peak I_Ca at 50 ms from data shown in E and F, including those in EGTA from Figure 4B. Number of cells in EGTA (1 mm), perforated-patch, and different concentrations of BAPTA (0.1, 0.3, 0.6, 1, 5 mm) are as follows: apical, 13, 5, 3, 5, 4, 5, 3; basal, 13, 7, 3, 4, 5, 4, 3. H, Estimation of the endogenous buffer concentration. The perforated-patch values of ΔC_m were extrapolated (dotted lines) to those obtained using different BAPTA concentrations (data as in G). Error bars indicate SEM.