4-aminopyridine restores conduction in heat-blocked sciatic branches.

We induced partial conduction block in rat sural and posterior tibial nerves by heating a short (5 mm) segment of the midportions of these branches to 45 degrees C until the amplitude of the elicited compound action potential was reduced by at least 50%, an effect that appeared to be irreversible without specific treatment. Excised branches studied in vitro were compared with branches heated in situ with an intact blood supply. The potassium channel blocker 4-aminopyridine (4-AP, 5 mM) was applied topically to the heated segments at intervals after injury. The amplitude of the compound action potential was restored to the control level in all preparations treated within 10 minutes after the induction of conduction block. The reversal appeared to be more rapid in the in vivo preparations, and it persisted for at least 60 minutes. The data suggest that paranodal potassium channel exposure may accompany direct thermal injury to the peripheral nerve.