Electrophysiological and ultrastructural studies on reversible neural conduction disturbance after high voltage discharge

High-voltage condenser discharges exerting a field strength of up to 1000 V/cm (discharge time constant 0.24-8 msec) applied to isolated sciatic frog nerve lead to disturbances of the propagation of action potentials including transient complete block of conduction. Such conduction disturbances are normally reversible within minutes. Inhibition of the activity of the membrane–bound Na+-K+ATPase prevents the recovery from conduction block. Withdrawal of external Ca2+ also prevents recovery, whereas blockade of protein synthesis by cycloheximide has no influence. The velocity of recovery depends on the temperature, with temperature coefficients (Q10) from 1.31 to 1.84 between 2° and 30°C. Transmission electron microscopy of nerves subjected to strong discharges shows alterations of the myelin sheath (splitting and cleft formation) which are, however, not specific for this mechanism of injury. No alterations are seen in the region of the free axoplasmic membrane of the node of Ranvier or in organelles. The results suggest a breakdown of the transmembrane ionic gradient causing the conduction disturbance.