Currents and di-8-ANEPPS transients elicited in response to a three-pulse stimulation protocol (data and model simulations). (A) Di-8-ANEPPS transients recorded under control conditions in response to three-pulse stimulation (see Materials and methods). The test pulses were −120, −80, −40, 0, 40, and 80-mV pulses from V_H = −20 mV (black, red, blue, green, dark blue, and orange traces, respectively). The deconvolution of ΔF/F (left vertical axis) into membrane potential (right vertical axis) was done according to the regression formula V_m = (ΔF/F − 0.035)/1.6 x 10⁻³ (in mV). (B) Current traces recorded using the same pulses as in A. (C) Di-8-ANEPPS transients recorded in the presence of 9-ACA in response to the same protocol as in A. (D) Current records (residual current) using the same pulses as in A in the presence of 9-ACA. (E) Model predictions of the TTS membrane potential assuming equal chloride permeability density in the TTS and surface membranes and the geometrical parameters of the fiber (see below). (F) Ionic currents associated with the simulated traces in E. Fiber parameters: radius = 31 μm; length = 372 μm; capacitance: 5.7 μF/cm².