Hyperexcitability of spinal sensory neurons contributes significantly to pain syndromes, for example, after nerve injury and in cases of inflammation. A method of dampening hyperexcitability of these neurons is expected to ameriorate neuropathic pain, and the targeting of sensory neuron-specific molecules may yield pain relief with minimal side effects. Sodium channels generate the inward currents that underlie action potentials. Several sodium channels have now been identified in spinal sensory neurons (e.g., dorsal root ganglia, DEG neurons). Small diameter DRG neurons, the majority of which are nociceptive, express sodium currents that are sensitive to the neurotoxin tetrodotoxin (TTX-S) and others that are resistant (TTX-R). TTX-R currents are increased in experimental models of inflammation. We have sequenced a novel rat TTX-R sodium channel, NaN, which is restricted in its expression to high threshold nociceptive neurons of DRG and trigeminal ganglia. We propose to sequence human NaN, to clones rat NaN cDNA in a mammalian expression vector, and to characterize the NaN expression and current in HEK293 cells. This represents a critical step toward developing molecular targets in cell-based assays for high throughput screening for agents that modify or block the activity of this sensory neuron-specific channel in vivo.
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