Magnesium influx in dialyzed squid axons.

The influx of magnesium from seawater into squid giant axons has been measured under conditions where internal solute control in the axon was maintained by dialysis. Mg influx is smallest (1 pmol/cm2 sec) when both Na and ATP have been removed from the axoplasm by dialysis. The addition of 3 mM ATP to the dialysis fluid gives a Mg influx of 2.5 pmol/cm2 sec while the addition of [Na]i and [ATP]i gives 3 pmol/cm2 sec as a value for Mg influx; this corresponds well with fluxes measured in intact squid giant axons. The Mg content of squid axons is 6 mmol/kg axoplasm; this is unaffected by soaking axons in Li or Na seawater for periods of up to 100 min.