Alteration of the electrical properties of myelinated nerve fibres exposed to a lipoprotein extracted from the serum of burnt patients.

The effects on the nodal membrane of a neurotoxic lipoprotein isolated from the serum of heavily burnt patients were analysed under current clamp and voltage clamp conditions. 1. After exposure of the node to the toxin, the only major modifications of the action potential are a slight increase in its duration, a slight decrease in its amplitude, and the appearance of a small after-depolarization. 2. A voltage clamp study revealed that the sodium and potassium conductances are markedly reduced, and that the rate of rise of the potassium current is slowed down by the toxin. While the activation of the sodium conductance is not modified, the inactivation is affected by the toxin: the steady-state inactivation-voltage curve is shifted toward negative potentials, and its slope is decreased; the inactivation time constant is decreased. All these effects are irreversible. 3. These modifications of the electrical properties of the nerve fibre membrane seem inadequate to explain the neurotoxicity of the lipoprotein from the serum of burnt humans.