The effect of salt or various cryoprotective agents on frog sciatic nerves

Desheathed frog sciatic nerves were tested for membrane damage by noting changes in their conduction velocity, externally recorded action potential, and absolute refractory period. Nerves were exposed for 45–60 min depending on the treatment to 1.5 osmolar environments consisting of concentrated Ringer's solution or Ringer's solution plus glycerol, sucrose, or dimethyl sulfoxide (DMSO). The nerves were exposed to these hypertonic solutions in one of four ways: (1) Gradual exposure plus gradual de-exposure, (2) Gradual exposure (plus direct de-exposure), (3) (direct exposure plus) plus gradual de-exposure, (4) Direct exposure (plus direct de-exposure). After treatment the nerves were allowed to recover for 45–60 min depending on the type of treatment in normal Ringer's solution. The results suggest the following: (1) Concentrated salt solutions damage nerve axons due to increased ion concentration rather than increased tonicity. (2) The effect of osmotic shock on sciatic nerves is relatively minor and completely reversible. (3) Axon membranes behave as simple permeability barriers with respect to sucrose and DMSO, but they appear to behave as dynamic entities which alter their metastable states with respect to concentrated salt or concentrated glycerol in Ringer's solution. (4) Freeze-thaw damage to sciatic nerve axon membranes—and perhaps to any cell membrane—is probably due to increased ionic concentration as well as increased osmolarity.