Abstract
Monophasic compound action potentials were recorded from Rana sciatic nerves. Three distinct peaks were observed and designated Aα, Aδ and C. All peaks were abolished by replacement of the external medium with Na +-free solution. However, the C peak alone was unaffected by external application of 1 μM tetrodotoxin (TTX), both A peaks were completely suppressed. The C peak was also the most resistant to chronic depolarization caused by increased external K +.K + (17.6 mM) solution reduced peak areas to 5 ± 4, 27 ± 11 and 63 ± 14% of control for Aa, Ab and C components. The C peak was therefore Na +-dependent, TTX-resistant and K +-depolarization resistant. These attributes are similar to those described for somatal TTX-resistant Na + channels in other species. But, application of 1 μM TTX to a K +-depolarized nerve caused a further reduction in C peak area, suggestive of a voltage-dependent block by TTX similar to that reported for cardiac muscle Na + channels.
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