Fig. 2.

Maximal synaptic Ca²⁺ influx varies with AZ position in IHCs: modiolar–pillar gradient. (A) The polar chart displays intensity of maximal AZ Ca²⁺ influx (ΔF_{−7 mV}/F₀) as a function of AZ position in live-imaging experiments. Modiolar and pillar refer to facing toward or away from the ganglion in the modiolus; apical and basal refer to the tonotopic axis of the organ of Corti. The radius of the inner circle is 3 µm. Data were pooled from 21 IHCs. (B) The polar chart displays locations and intensity of AZ TAMRA-peptide fluorescence intensity in live-imaging experiments. Data were pooled from 14 IHCs. (C) Maximal AZ Ca²⁺ influx (red, 202 AZs of 21 cells) and integrated AZ Ca_v1.3 immunofluorescence (black, 187 AZs of 12 cells) as a function of position along the modiolar–pillar axis. Solid lines represent linear regressions and r indicates the Pearson’s correlation coefficient. (D) The box plot (10, 25, 50, 75, and 90% percentiles) shows the statistics of maximal AZ Ca²⁺ influx for the modiolar (140 AZs) and pillar (82 Azs) halves of the same IHCs as in A. No significant difference was reported by Wilcoxon rank sum test (P = 0.33). (E) The box plot shows the statistics (as in D) of Ca_v1.3 immunofluorescence intensity for AZs of 12 cells, which was stronger on the modiolar (109 AZs) than on the pillar side (78 AZs, P < 0.001). (F) Spatial gradient of AZ TAMRA-peptide fluorescence in live-imaging (red, 14 IHCs) and CtBP2/RIBEYE immunofluorescence (black circle, same AZs as in E) along the modiolar–pillar axis. (G and H) The box plot shows the statistics (as in D) of the TAMRA-peptide fluorescence intensity (G) and CtBP2/RIBEYE immunofluorescence intensity (H). Both measures indicate greater CtBP2/RIBEYE abundance on the modiolar side than on the pillar side: G, P < 0.05 and H, P < 0.001.