Contactin regulates the current density and axonal expression of tetrodotoxin-resistant but not tetrodotoxin-sensitive sodium channels in DRG neurons.
Contactin, a glycosyl-phosphatidylinositol (GPI)-anchored predominantly neuronal cell surface glycoprotein, associates with sodium channels Nav1.2, Nav1.3 and Nav1.9, and enhances the density of these channels on the plasma membrane in mammalian expression systems. However, a detailed functional analysis of these interactions and of untested putative interactions with other sodium channel isoforms in mammalian neuronal cells has not been carried out. We examined the expression and function of sodium channels in small-diameter dorsal root ganglion (DRG) neurons from contactin-deficient (CNTN-/-) mice, compared to CNTN+/+ litter mates. Nav1.9 is preferentially expressed in isolectin B4 (IB4)-positive neurons and thus we used this marker to subdivide small-diameter DRG neurons. Using whole-cell patch-clamp recording, we observed a greater than two-fold reduction of tetrodotoxin-resistant (TTX-R) Nav1.8 and Nav1.9 current densities in IB4+ DRG neurons cultured from CNTN-/- vs. CNTN+/+ mice. Current densities for TTX-sensitive (TTX-S) sodium channels were unaffected. Contactin's effect was selective for IB4+ neurons as current densities for both TTX-R and TTX-S channels were not significantly different in IB4- DRG neurons from the two genotypes. Consistent with these results, we have demonstrated a reduction in Nav1.8 and Nav1.9 immunostaining on peripherin-positive unmyelinated axons in sciatic nerves from CNTN-/- mice but detected no changes in the expression for the two major TTX-S channels Nav1.6 and Nav1.7. These data provide evidence of a role for contactin in selectively regulating the cell surface expression and current densities of TTX-R but not TTX-S Na+ channel isoforms in nociceptive DRG neurons; this regulation could modulate the membrane properties and excitability of these neurons.
Rush
Anthony M
AM
Department of Neurology, Yale School of Medicine, LCI 707, 333 Cedar St., New Haven, CT 06510, USA.
Craner
Matthew J
MJ
Kageyama
Takashi
T
Dib-Hajj
Sulayman D
SD
Waxman
Stephen G
SG
Ranscht
Barbara
B
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D058966:Contactins; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D062559:NAV1.8 Voltage-Gated Sodium Channel; D062558:NAV1.9 Voltage-Gated Sodium Channel; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects / Q000378:metabolism; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000187:drug effects / Q000378:metabolism; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D037121:Plant Lectins; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D015816:Cell Adhesion Molecules, Neuronal; D058966:Contactins; C045475:Griffonia simplicifolia lectins; D062559:NAV1.8 Voltage-Gated Sodium Channel; D062558:NAV1.9 Voltage-Gated Sodium Channel; D009479:Neuropeptides; D037121:Plant Lectins; C568318:Scn10a protein, mouse; C491885:Scn11a protein, mouse; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin