Fig. 5. Measurement of the reversal potential during a membrane action potential. All recordings were taken from a Loligo pealei axon at 15°C. Holding potential, just before current clamping, was -65 mV. Axons were bathed in 10K ASW (see Materials and methods). (A) A single membrane action potential. (Bi) Seven similar action potential recording, which have been voltage-clamped after 700 µs, superimposed. Voltage-clamp potentials are from -70 mV to +50 mV in increments of 20 mV. (Bii) Paired current traces for voltage traces in Bi demonstrating instantaneous jumps. (C) Results from nine experiments similar to that in B but interrupted at different times. Reversal potential (E_rev), determined from instantaneous current/voltage plots, plotted as a function of time and superimposed onto an action potential.