Fig. 6 . Measurement of the K⁺ conductance (gK) and Na⁺ conductance (gNa) during a membrane action potential. All recordings were made at 10°C. Holding potential was -65 mV. Axons were bathed in 10K ASW (see Materials and methods). For gK experiments, time points are at 100 µs intervals for Loligo pealei and at 200 µs intervals for L. plei and Sepioteuthis sepioidea. For gNa, time points are at 20 µs intervals for L. pealei and at 50 µs intervals for L. plei and S. sepioidea. (Ai) Membrane action potential from L. pealei interrupted by voltage-clamp to -70mV (K⁺ equilibrium potential, E_K) after 700 µs (arrow). (Aii) Matching current recording. The value of the instantaneous current at the time of voltage-clamp switch-on corresponds to the Na⁺ current (I_Na). (Bi) Membrane action potential from L. pealei interrupted by voltage-clamp to +55 mV (Na⁺ equilibrium potential, E_Na) after 2 ms (arrow). (Bii) Matching current recording. The value of the instantaneous current at the time of voltage-clamp switch-on corresponds to the K⁺ current (I_K). (C—E) Experiments similar to those in A and B, performed at many `interruption' points were used to derive time courses for gK and gNa from axons of L. pealei, L. plei and S. sepioidea. In each panel, an action potential (solid line) is superimposed on the time course for gNa ([UNK]) and gK ().

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