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The Journal of Neurophysiology Vol. 84 No. 2 August 2000, pp. 710-718
Copyright ©2000 by the American Physiological Society
-SNS Produces the Slow TTX-Resistant Sodium Current in Large
Cutaneous Afferent DRG Neurons
Department of Neurology and Paralyzed Veterans Association/Eastern Paralyzed Veterans Association Neuroscience Research Center, Yale Medical School, New Haven 06510; and Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare Center, West Haven, Connecticut 06516
Renganathan, M.,
T. R. Cummins,
W. N. Hormuzdiar, and
S. G. Waxman.
-SNS Produces the Slow TTX-Resistant Sodium Current in Large
Cutaneous Afferent DRG Neurons. J. Neurophysiol. 84: 710-718, 2000. In this study, we used sensory
neuron specific (SNS) sodium channel gene knockout (
/) mice to ask
whether SNS sodium channel produces the slow Na+
current ("slow") in large (>40 µm diam) cutaneous afferent
dorsal root ganglion (DRG) neurons. SNS wild-type (+/+) mice were used as controls. Retrograde Fluoro-Gold labeling permitted the definitive identification of cutaneous afferent neurons. Prepulse inactivation was
used to separate the fast and slow Na+ currents.
Fifty-two percent of the large cutaneous afferent neurons isolated from
SNS (+/+) mice expressed only fast-inactivating Na+ currents ("fast"), and 48% expressed
both fast and slow Na+ currents. The fast and
slow current densities were 0.90 ± 0.12 and 0.39 ± 0.16 nA/pF, respectively. Fast Na+ currents were
blocked completely by 300 nM tetrodotoxin (TTX), while slow
Na+ currents were resistant to 300 nM TTX,
confirming that the slow Na+ currents observed in
large cutaneous DRG neurons are TTX-resistant (TTX-R). Slow
Na+ currents could not be detected in large
cutaneous afferent neurons from SNS (/) mice; these cells expressed
only fast Na+ current, and it was blocked by 300 nM TTX. The fast Na+ current density in SNS
(/) neurons was 1.47 ± 0.14 nA/pF, approximately 60% higher
than the current density observed in SNS (+/+) mice (P < 0.02). A low-voltage-activated TTX-R Na+
current ("persistent") observed in small C-type neurons is not present in large cutaneous afferent neurons from either SNS (+/+) or
SNS (/) mice. These results show that the slow TTX-R
Na+ current in large cutaneous afferent DRG is
produced by the SNS sodium channel.
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