The presence and role of the tetrodotoxin-resistant sodium channel Nav1. 9 (NaN) in nociceptive primary afferent neurons

X Fang, L Djouhri, JA Black, SD Dib-Hajj… - Journal of …, 2002 - Soc Neuroscience
X Fang, L Djouhri, JA Black, SD Dib-Hajj, SG Waxman, SN Lawson
Journal of Neuroscience, 2002Soc Neuroscience
This is the first examination of sensory receptive properties and associated
electrophysiological properties in vivo of dorsal root ganglion (DRG) neurons that express
the TTX-resistant sodium channel Nav1. 9 (NaN). Intracellular recordings in lumbar DRGs in
Wistar rats enabled units with dorsal root C-, Aδ-, or Aα/β-fibers to be classified as
nociceptive, low-threshold mechanoreceptive (LTM), or unresponsive. Intracellular dye
injection enabled subsequent immunocytochemistry for Nav1. 9-like immunoreactivity …
This is the first examination of sensory receptive properties and associated electrophysiological properties in vivo of dorsal root ganglion (DRG) neurons that express the TTX-resistant sodium channel Nav1.9 (NaN). Intracellular recordings in lumbar DRGs in Wistar rats enabled units with dorsal root C-, Aδ-, or Aα/β-fibers to be classified as nociceptive, low-threshold mechanoreceptive (LTM), or unresponsive. Intracellular dye injection enabled subsequent immunocytochemistry for Nav1.9-like immunoreactivity (Nav1.9-LI).
Nav1.9-LI was expressed selectively in nociceptive-type (C- and A-fiber nociceptive and C-unresponsive) units. Of the nociceptive units, 64, 54, and 31% of C-, Aδ-, and Aα/β-fiber units, respectively, were positive for Nav1.9-LI. C-unresponsive units were included in the nociceptive-type group on the basis of their nociceptor-like membrane properties; 91% were positive. Nav1.9-LI was undetectable in Aδ- or Aα/β-fiber LTM units and in one C-LTM unit. Nav1.9-LI intensity was correlated negatively with soma size and conduction velocity in nociceptive units and with conduction velocity in C-fiber units. There was a positive correlation with action potential rise time in nociceptive-type units with membrane potentials equal to or more negative than –50 mV. The data provide direct evidence that Nav1.9 is expressed selectively in (but not in all) C- and A-fiber nociceptive-type units and suggest that Nav1.9 contributes to membrane properties that are typical of nociceptive neurons.
Soc Neuroscience