centration (45). TRPV1 has been reported to be primarily
expressed in peripheral afferent sensory neurons type C and in
A fibers originating from dorsal root ganglia (8). However,
recent studies have also demonstrated that TRPV1 is expressed
in some nonneuronal tissues and cells (2, 6, 25, 35, 41), where
it functions to regulate inflammatory cytokine production following exposure to TRPV1 agonists (12, 21, 29, 33, 48).
Although TRPV1 has been considered as a molecular sensor of
chemical and physical stimuli in nonneuronal cells, the precise
function of this protein is not yet clear.
Human esophageal epithelium is continuously exposed to
physical stimuli or gastric acid that sometimes causes inflammation of the mucosa. Acute or chronic exposure of the human
esophagus to acid can lead to hypersensitivity of the mucosa.
Gastroesophageal reflux disease (GERD), which is induced by
reflux of the gastric and duodenal contents into the esophagus,
has recently come to be recognized as a serious clinical
problem that manifests as reflux symptoms, hurt burn, and
chest pain. The occurrence of GERD is related to relaxation of
the lower esophageal sphincter (LES) and to increased gastric
acid secretion. Moreover, inflammatory cytokines, leukocytes,
and oxidative stress have been demonstrated to be involved in
the hypersensitivity of reflux esophagitis (30, 43, 44, 46).
Interestingly, TRPV1 expression has been detected in sensory
nerve fibers of esophageal mucosa from patients with GERD or
nonerosive reflux disease (5, 28). This finding might suggest
that esophageal hypersensitivity is also associated with acidinduced activation of TRPV1 (3, 12) because TRPV1 is believed to be a mediator of neurogenic inflammation. However,
it remains unknown whether TRPV1 is expressed in human
esophageal epithelial cells or whether TRPV1 mediates inflammation of the esophagus.
In this study, we investigated the expression and function of
TRPV1 in the human esophageal epithelial cell line Het1A,
with a specific focus on the role of oxidative stress.
MATERIALS AND METHODS
Reagents. Capsaicin, capsazepine, and ruthenium red were obtained from Sigma-Aldrich (St. Louis, MO). Stock concentrations of
capsaicin (100 mM), capsazepine (100 mM), and ruthenium red (10
mM) were dissolved in ethanol, dimethyl sulfoxide, and distilled
water and were diluted in media to the appropriate concentration.
Redox Sensor Red CC-1 was purchased from Molecular Probes
(Eugene, OR). Biotinylated cysteine was prepared as previously
described (15, 20). 4-Hydroxy-2-nonenal (HNE) was a generous gift
of Dr. Uchida, Graduate School of Bioagricultural Sciences, Nagoya
University (Nagoya, Japan). Polyclonal rabbit and goat anti-TRPV1