Comparison of results in apical and basal OHCs. (A) Variance versus mean current plots for two OHCs from apex (P5, top) and base (P3, bottom); red parabolic line fit to experimental recordings gave similar single-channel currents, i, with different channel numbers, N_MET. (B) Linear approximation of variance versus mean current for small open probabilities (5% of maximum current) from apical (top) and basal OHCs (bottom) fit with straight lines to give i = −3.5 pA (apex) and −3.4 pA (base). (C) Collected results of OHC single-channel currents for unitary events after BAPTA treatment for apex (n = 5) and base (n = 4) and for noise analysis for apex (n = 10) and base (n = 8). Means ± SD (black circles). (D) Number of channels inferred from noise analysis plotted against maximum MET current for apical and basal OHCs fit with a line through the origin of inverse slope of 3.7 ± 0.1 pA. IHC results (crosses), when fit independently, gave single-channel conductance of 3.9 ± 0.2 pS. Holding potential, −84 mV. Collected measurements on apical OHCs and IHCs from P4–P7 mice and on basal OHCs from P3–P4 mice.