Voltage step protocols highlight different fluorescent responses for each label. (A) Representative current and ΔF recordings for ALEXA-488 (left) and MTS-TAMRA (right) labeled oocytes using an 8-ms voltage step (inset) showing current (upper) and fluorescence (below). The traces were signal averaged eightfold to improve the signal-to-noise ratio and separated vertically for visualization. ΔF shown as a percentage of background fluorescence. (Β) ΔF-V for ALEXA-488–labeled cells. The peak ΔF at each voltage at the end of the 8 ms step was first fit with the Boltzmann function and normalized for each cell to ∆F^max before pooling. Continuous curve is Boltzmann fit with V_0.5^F = −107.8 ± 5.0 mV; z^F = 0.73 ± 0.05; mean ± SE (n = 9). (C) Voltage dependence of time course for rising phase of ΔF for ALEXA-488–labeled cells (same data set as in B) obtained by fitting with a single exponential. It was not possible to resolve reliable fits for voltages above −60 mV. The continuous line is a free fit with a two-state model equation (assuming a symmetrical energy barrier) (⁠$τF=1/kfe−V2kTezF+kbe+V2kTezF$⁠, where k_f,b are the forward and backward rates, respectively, and z^F is the apparent valence. The fit yielded the following parameters: z^F = 0.82 ± 0.15; k_f = 0.024 ± 0.009 and k_b = 0.76 ± 0.24; mean ± SE (n = 9). (D) Representative current and ΔF recordings for ALEXA-488 (left) and MTS-TAMRA (right) labeled oocytes in response to a sequence of prepulses to −160 mV with increasing length (inset) showing current (upper) and fluorescence (below). The traces were signal averaged eightfold to improve the signal-to-noise ratio. ΔF shown as a % of background fluorescence.