Figure 7.

Concentration dependence of exogenous Ca²⁺ chelators. Ca²⁺ efficiency of exocytosis (Δ_Cm/Q_Ca obtained for a 25 ms depolarization from −80 mV to −10 mV) normalized to the maximum Ca²⁺ efficiency (obtained with 0.1 mm BAPTA) as a function of different concentrations of intracellular BAPTA and EGTA in VHC-I (A) and IHCs (B). The dotted red curves fit EGTA data using the linearized reaction diffusion equations of Ca²⁺ described in Materials and Methods. Best fits were obtained with a mean coupling distance between Ca²⁺ channels and sensors r of 46 ± 12 nm (A, VHC-I) and 70 ± 20 nm (B, IHCs). Solid lines indicate the fit with a Hill sigmoidal function. It is important to note that this coupling distance r was obtained for a somewhat long 25 ms depolarization at maximal channel open probability. It may likely reflect here the interacting coupling distance between individual Ca²⁺ nanodomains described in Figure 6.