a–c Histograms displaying the number of dye-filled IHCs per loading at 3 different developmental stages. d Representative whole-cell Ca2+-currents ([Ca2+]e = 5 mM) of a single IHC (red), 2 (green), and 3 (blue) coupled IHCs evoked by step depolarizations from −70 to 80 mV at P21–35 (as in e, f). Current-voltage relationships (IVs) in single and dye-coupled IHCs with mean (line) ± S.E.M. (shaded areas). Scatter plots and line fits relating ICaMax (e) and Irest (e′) currents against Cm values according to the number of dye-coupled IHCs. Cm membrane capacitance, ICaMax maximal Ca2+-current, IHC inner hair cell, Irest resting current.