Figure 7. Reduced Ca²⁺-sensitivity of exocytosis in Otof ^C2C/C2C IHCs.

(A) Mean ΔC_m response curves (top) and normalized exocytosis rates (dC_m/dt) (bottom), with mean intracellular fluorescent Ca² signals of OGB-5N (green traces) recorded simultaneously after Ca²⁺ uncaging (purple arrowhead) in P14-P16 Otof ^C2C/+ (in black) and Otof ^C2C/C2C (in blue) IHCs. (B) Left: For each recorded Otof ^C2C/+ (in black) and Otof ^C2C/C2C (in blue) IHC, the rate of exocytosis was plotted as a function of [Ca²⁺]_i, and each data set was fitted with a Hill function y = V_max.xⁿ /(EC₅₀ⁿ + xⁿ). Right: Mean cooperativity and Ca²⁺-affinity of release in Otof ^C2C/+ and Otof ^C2C/C2C IHCs. Note that for 3 out of 6 Otof ^C2C/C2C IHCs, the fit of the sigmoidal Hill function to the data was only partial. For those IHCs, the Ca²⁺ affinity was estimated as the value of [Ca²⁺] for which dC_m/dt = 0.5, rather than the EC₅₀ of the fitted Hill function, which was larger. Data information: in (B), one IHC of each genotype was removed because of the lack of experimental points for a reliable fitting with a Hill function. In (A–B), data are presented as the mean ± SEM. **p<0.01, ns not significant (Mann-Whitney test).