Changes in Fluo-5N fluorescence induced by depolarizing pulses of increasing amplitude. (A) Simultaneous recordings of membrane currents (top trace) and changes in Fluo-5N fluorescence (middle traces) in the same control fiber (OF1 mouse) in response to depolarizing pulses of 1 s duration and increasing amplitudes delivered every 2 min (bottom traces). Images recorded for fluorescence measurements were captured at a frequency of 25 Hz. (B) Relationship between the mean changes in Fluo-5N fluorescence and membrane potential. The change in Fluo-5N fluorescence induced by depolarization corresponds to the measured difference between the minimal value of fluorescence recorded during the voltage pulse and the baseline value before the pulse. The numbers above each data point indicate the number of cells tested. Error bars indicate mean ± SEM.