Sodium influxes in internally perfused squid giant axon during voltage clamp

1. An experimental method for measuring ionic influxes during voltage clamp in the giant axon of Dosidicus is described; the technique combines intracellular perfusion with a method for controlling membrane potential.

2. Sodium influx determinations were carried out while applying rectangular pulses of membrane depolarization. The ratio `measured sodium influx/computed ionic flux during the early current' is 0·92 ± 0·12.

3. Plots of measured sodium influx and computed ionic flux during the early current against membrane potential are very similar. There was evidence that the membrane potential at which the sodium influx vanishes is the potential at which the early current reverses.