Functional tetrodotoxin-resistant Na+ channels are expressed presynaptically in rat dorsal root ganglia neurons

• Published in: Neuroscience Vol. 159; no. 2; pp. 559 - 569
• Main Authors: Medvedeva, Y.V, Kim, M.-S, Schnizler, K, Usachev, Y.M
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 17-03-2009; Elsevier
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Anesthetics, Local - pharmacology; Animals; Animals, Newborn; Benzofurans - metabolism; Biological and medical sciences; Biophysics; Calcium - metabolism; Cells, Cultured; Coculture Techniques; Disks Large Homolog 4 Protein; Electric Stimulation; Ethers, Cyclic - metabolism; Extracellular Fluid - drug effects; Extracellular Fluid - metabolism; Fundamental and applied biological sciences. Psychology; Ganglia, Spinal - cytology; Intracellular Signaling Peptides and Proteins - metabolism; Ion Channel Gating - drug effects; Lidocaine - pharmacology; Membrane Proteins - metabolism; Nav1.8; NAV1.8 Voltage-Gated Sodium Channel; Nav1.9; NAV1.9 Voltage-Gated Sodium Channel; Nerve Tissue Proteins - metabolism; Neurology; Neuropeptides - metabolism; Patch-Clamp Techniques - methods; Presynaptic Terminals - metabolism; Rats; Rats, Sprague-Dawley; SBFI; Sensory Receptor Cells - cytology; Sensory Receptor Cells - drug effects; sensory synapse; Sodium - metabolism; Sodium Channel Blockers - pharmacology; Sodium Channels - drug effects; Sodium Channels - metabolism; Spinal Cord - cytology; Synapses - drug effects; Synapses - physiology; synaptic transmission; tetrodotoxin; Tetrodotoxin - pharmacology; Vertebrates: nervous system and sense organs; sensory synapse; [Na +] i; intracellular Ca 2+ concentration; intracellular Na + concentration; feline immunodeficiency virus; ara-C; tetrodotoxin-sensitive; EGFP; voltage-gated sodium channel; P; SC; HH buffer; postnatal day; TTX; TTX-S; synaptic transmission; TTX-R; EPSC; Hepes-buffered recording solution; spinal cord; excitatory postsynaptic current; tetrodotoxin-resistant; dorsal root ganglia; [Ca 2+] i; VGSC; FIV; PSD95; SBFI; enhanced green fluorescent protein; DRG; postsynaptic density 95 protein; tetrodotoxin; cytosine-A-D-arabinofuranoside; Nav1.9; Nav1.8; Spinal cord; Rat; Rodentia; Central nervous system; Ionic channel; Vertebrata; Synapse; Mammalia; Neuron; Sodium; Synaptic transmission; Animal; Spinal ganglion
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2008.12.029

Abstract The tetrodotoxin-resistant (TTX-R) voltage-gated Na+ channels Nav 1.8 and Nav 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 Nav 1.8- and Nav 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 [Ca2+ ]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.