C-FIBER GENERATES A SLOW NA+ SPIKE IN THE FROG SCIATIC-NERVE

The present study was carried out to examine the properties of A and C fibers in the bullfrog sciatic nerves by applying several agents through perfusing solutions between stimulating and recording electrodes. The compound action potentials (CAPs) of A(beta) and A(delta) fibers were tetrodotoxin (TTX)-sensitive and were abolished in Na+-free solution. However, C fiber CAP was TTX-insensitive although CAP disappeared in Na+-free solution. Moreover C fiber CAP was not blocked by Ca2+ channel blockers and its chronaxy (2 ms) and conduction velocity (0.70 m/s) indicate that the time constant of C fiber CAP is relatively large (2.88 ms). These suggest that a slow Ne channel, which is TTX-resistant, contributes to C fiber action potentials.