Noninactivating, tetrodotoxin-sensitive Na+ conductance in peripheral axons.
A noninactivating, persistent sodium current has been demonstrated previously in dorsal root ganglia neurons and in rat optic nerve. We report here that Na(+) channel blockade with tetrodotoxin (TTX) in isolated dorsal and ventral roots elicits membrane hyperpolarization, suggesting the presence of a persistent Na(+) current in peripheral axons. We used a modified sucrose-gap chamber to monitor resting and action potentials and observed a hyperpolarizing shift in the nerve potential of rat dorsal and ventral roots by TTX. The block of transient inward Na(+) currents was confirmed by the abolition of compound action potentials (CAPs). Moreover, depolarization of nerve roots by elevating extracellular K(+) concentrations to 40 mM eliminated CAPs but did not significantly alter TTX-induced hyperpolarizations, indicating that the persistent Na(+) currents in nerve roots are not voltage-dependent. Tetrodotoxin-sensitive persistent inward Na(+) currents are present in both dorsal and ventral root axons at rest and may contribute to axonal excitability.
Tokuno
Hajime A
HA
Rehabilitation Research Center, VA Hospital, West Haven, Connecticut 06516, USA.
Kocsis
Jeffery D
JD
Waxman
Stephen G
SG
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects; D010525:Peripheral Nerves / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013126:Spinal Nerve Roots / Q000166:cytology / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology*
D015222:Sodium Channels; D013779:Tetrodotoxin; D011188:Potassium