Inhibition of sympathetic N-type voltage-gated Ca2+ current underlies the reduction in norepinephrine release during colitis

Abstract

Inflammatory bowel diseases (IBD) are associated with altered neuronal regulation of the gastrointestinal (GI) tract and impairment of norepinephrine release from sympathetic varicosities. The sympathetic innervation of the GI tract modulates motility, blood flow, and secretion, and therefore defective norepinephrine release may contribute to symptom generation in IBD. Accordingly, our aim here was to utilize the mouse model of dextran sulfate sodium (DSS; 5% wt/vol) of IBD to determine how norepinephrine release is reduced during GI inflammation. We hypothesized that the inflammation-induced reduction in norepinephrine release was due to inhibition of voltage-gated Ca2+ current ( ICa) in prevertebral sympathetic neurons. We compared [3H]norepinephrine release in the colon and jejunum and ICa amplitude in superior mesenteric ganglion (SMG) neurons from control mice and mice with DSS-induced colitis. Changes to voltage-gated Ca2+ channels were investigated by fura 2-AM Ca2+ imaging, perforated patch-clamp electrophysiology, and real-time PCR. Depolarization-induced norepinephrine release from the inflamed colon and uninflamed jejunum was significantly impaired in mice treated with DSS, as was depolarization-induced Ca2+ influx in SMG neurons. Colitis reduced ICa in SMG neurons by inhibiting ω-conotoxin GVIA (300 nM)-sensitive N-type Ca2+ channels. The ω-conotoxin GVIA-sensitive component of norepinephrine release was significantly smaller in the colon during colitis. The inhibition of ICa was accompanied by a decrease in mRNA encoding the Ca2+ channel alpha subunit (CaV 2.2) and a rightward shift in the voltage dependence of activation of ICa. These findings suggest that DSS-induced colitis attenuates norepinephrine release in the colon and jejunum due to inhibition of N-type voltage-gated Ca2+ channels. This may contribute to functional alterations in both inflamed and uninflamed regions of the GI tract during inflammation.