Fig. 3. Separation of Na⁺ and K⁺ currents from voltage-clamped axons. (A) Voltage-clamp recording from a Sepioteuthis sepioidea axon at 20°C. The arrow indicates the start of a voltage step to 0 mV. (B) Family of K⁺ currents from a S. sepioidea axon at 20°C in the presence of tetrodotoxin (TTX). At the arrow, voltages were stepped from the holding potential to -40 mV, -20 mV, 0 mV, 20 mV, 40 mV and 60 mV. (C) Measurement of Na⁺ current (I_Na) in a Loligo plei axon at 10.6°C by TTX subtraction. (i) Two traces after voltages had been stepped from the holding potential to -10 mV, before and after TTX, superimposed. (ii) I_Na resulting from the TTX trace being subtracted from non-TTX trace. (iii) A family of I_Na traces from the same axon, using the same technique, after voltage steps to -30 mV, -10 mV, 10 mV, 30 mV, 50 mV and 70 mV. All holding potentials were -70 mV. The external solution was 10K ASW (see Materials and methods). The first points of each trace are at 0 µA.