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.
Pubmed ID: 19162133 RIS Download
Mesh terms: Action Potentials | Anesthetics, Local | Animals | Animals, Newborn | Benzofurans | Biophysics | Calcium | Cells, Cultured | Coculture Techniques | Electric Stimulation | Ethers, Cyclic | Extracellular Fluid | Ganglia, Spinal | Intracellular Signaling Peptides and Proteins | Ion Channel Gating | Lidocaine | Membrane Proteins | NAV1.8 Voltage-Gated Sodium Channel | NAV1.9 Voltage-Gated Sodium Channel | Nerve Tissue Proteins | Neuropeptides | Patch-Clamp Techniques | Presynaptic Terminals | Rats | Rats, Sprague-Dawley | Sensory Receptor Cells | Sodium | Sodium Channel Blockers | Sodium Channels | Spinal Cord | Synapses | Tetrodotoxin
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