Sodium and potassium ion effluxes from squid axons under voltage clamp conditions.

Squid giant axons loaded with Na(24) were subjected to short duration (0.5 msec.) clamped depolarizations of about 100 mv at frequencies of 20/sec. and 60/sec. while in choline sea water. Under such conditions the early outward current was just about maximal at the time of termination of the clamping pulse. An integration of the early current versus time record gave 1.2 mucoulomb/cm(2) pulse, while a measurement of the extra Na(24) efflux resulting from repetitive pulsing gave a charge transfer of 1.4 mucoulomb/cm(2) pulse. In sodium-containing sea water and with pulses 50-75 mv more positive than E(Na) the Na(24) efflux is about 3 times the measured charge transfer. The efflux of K(42) from a previously loaded axon into normal sea water is only 50 per cent of the measured charge transfer when the membrane is held for about 5 msec. at a potential such that there is no early current, and such pulses are at 10-20/sec. The experiments appear to confirm the suggestion that the early current during bioelectric activity is sodium but provide unsatisfactory support for the identification of the delayed but sustained current solely with potassium ions. Resting Na(+) efflux is 0.6 pmole/cm(2) sec. mmole [Na](1), while the apparent K(+) efflux is about 250 pmole/cm(2) sec. and is little affected by hyperpolarization.