Voltage dependence of average ICl, PO, fluorescence changes, and attenuation obtained from fibers stimulated with the three-pulse protocol. (A) Plot of the average peak 9-ACA–dependent ICl as a function of Vm at P2. (B) Relative PO was obtained from current tails at the onset of P3 and is plotted versus Vm at P2. The solid line corresponds to the Boltzmann fit to the data. The red trace in the inset is the h∞(V) function in the TTS model calculated with the parameters listed in the Table A2 of the Appendix, except that = 0.04 ms−1, kα = 47 mV, and Vβ = −100 mV. The black symbols in the inset are PO values calculated from model simulations of ICl using an identical open channel chloride permeability (PCl = 2.7 × 10−5 cm/s) at the surface and TTS membrane compartments (the fiber radius was assumed to be 26 μm). (C) The solid and open circles are the ΔF/F changes in di-8-ANEPPS fluorescence recorded early during P2 in the absence and presence of 9-ACA, respectively, are plotted versus Vm at P2. The ΔF/F difference between average data points (9-ACA minus control) are plotted in the inset. (D) Average peak attenuations (%) at various P2 are plotted versus Vm at P2. The data in this figure were obtained from five fibers voltage clamped at VH = −20 mV. The arrows in each graph indicate VH. Statistical significance with respect to peak attenuation values at −140 mV is denoted by *. Statistical significance with respect to values at −120 mV is denoted by #. The symbol o indicates significance with respect to all data at negative voltages.
