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This Article Full Text Full Text (PDF) All Versions of this Article: 99/4/1917    most recent 01170.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Schofield, G. G. Articles by Ikeda, S. R. Search for Related Content PubMed PubMed Citation Articles by Schofield, G. G. Articles by Ikeda, S. R.

Properties of Wild-Type and Fluorescent Protein-Tagged Mouse Tetrodotoxin-Resistant Sodium Channel (Na_V1.8) Heterologously Expressed in Rat Sympathetic Neurons

¹Department of Physiology, Tulane University Health Sciences Center, New Orleans, Louisiana; and ²Laboratory of Molecular Physiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland

Submitted 22 October 2007; accepted in final form 12 February 2008

The tetrodotoxin (TTX)-resistant Na⁺ current arising from Na_V1.8-containing channels participates in nociceptive pathways but is difficult to functionally express in traditional heterologous systems. Here, we show that injection of cDNA encoding mouse Na_V1.8 into the nuclei of rat superior cervical ganglion (SCG) neurons results in TTX-resistant Na⁺ currents with amplitudes equal to or exceeding the currents arising from natively expressing channels of mouse dorsal root ganglion (DRG) neurons. The activation and inactivation properties of the heterologously expressed Na_V1.8 Na⁺ channels were similar but not identical to native TTX-resistant channels. Most notably, the half-activation potential of the heterologously expressed Na_V1.8 channels was shifted about 10 mV toward more depolarized potentials. Fusion of fluorescent proteins to the N- or C-termini of Na_V1.8 did not substantially affect functional expression in SCG neurons. Unexpectedly, fluorescence was not concentrated at the plasma membrane but found throughout the interior of the neuron in a granular pattern. A similar expression pattern was observed in nodose ganglion neurons expressing the tagged channels. In contrast, expression of tagged Na_V1.8 in HeLa cells revealed a fluorescence pattern consistent with sequestration in the endoplasmic reticulum, thus providing a basis for poor functional expression in clonal cell lines. Our results establish SCG neurons as a favorable surrogate for the expression and study of molecularly defined Na_V1.8-containing channels. The data also indicate that unidentified factors may be required for the efficient functional expression of Na_V1.8 with a biophysical phenotype identical to that found in sensory neurons.