title: Functional tetrodotoxin-resistant Na(+) channels are expressed presynaptically in rat dorsal root ganglia neurons.
abstract: The tetrodotoxin-resistant (TTX-R) voltage-gated Na(+) channels Na(v)1.8 and Na(v)1.9 are expressed by a subset of primary sensory neurons and have been implicated in various pain states. Although recent studies suggest involvement of TTX-R Na(+) channels in sensory synaptic transmission and spinal pain processing, it remains unknown whether TTX-R Na(+) channels are expressed and function presynaptically. We examined expression of TTX-R channels at sensory synapses formed between rat dorsal root ganglion (DRG) and spinal cord (SC) neurons in a DRG/SC co-culture system. Immunostaining showed extensive labeling of presynaptic axonal boutons with Na(v)1.8- and Na(v)1.9-specific antibodies. Measurements using the fluorescent Na(+) indicator SBFI demonstrated action potential-induced presynaptic Na(+) entry that was resistant to tetrodotoxin (TTX) but was blocked by lidocaine. Furthermore, presynaptic [Ca(2+)](i) elevation in response to a single action potential was not affected by TTX in TTX-resistant DRG neurons. Finally, glutamatergic synaptic transmission was not inhibited by TTX in more than 50% of synaptic pairs examined; subsequent treatment with lidocaine completely blocked these TTX-resistant excitatory postsynaptic currents. Taken together, these results provide evidence for presynaptic expression of functional TTX-R Na(+) channels that may be important for shaping presynaptic action potentials and regulating transmitter release at the first sensory synapse.
authors.affiliation: Department of Pharmacology, University of Iowa, Carver College of Medicine, 2-250 BSB, 51 Newton Road, Iowa City, IA 52242, USA.
authors.forename: Y V
authors.initials: YV
authors.lastname: Medvedeva
authors.forename: M-S
authors.initials: MS
authors.lastname: Kim
authors.forename: K
authors.initials: K
authors.lastname: Schnizler
authors.forename: Y M
authors.initials: YM
authors.lastname: Usachev
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001572:Benzofurans / Q000378:metabolism; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018920:Coculture Techniques; D000076122:Disks Large Homolog 4 Protein; D004558:Electric Stimulation; D004988:Ethers, Cyclic / Q000378:metabolism; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D008012:Lidocaine / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D062559:NAV1.8 Voltage-Gated Sodium Channel; D062558:NAV1.9 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000166:cytology* / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013116:Spinal Cord / Q000166:cytology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D000779:Anesthetics, Local; D001572:Benzofurans; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D004988:Ethers, Cyclic; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D062559:NAV1.8 Voltage-Gated Sodium Channel; D062558:NAV1.9 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C568319:Scn10a protein, rat; C113705:Scn11a protein, rat; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C061665:sodium-binding benzofuran isophthalate; D013779:Tetrodotoxin; D008012:Lidocaine; D012964:Sodium; D002118:Calcium