Gastroenterology

Gastroenterology

Volume 137, Issue 2, August 2009, Pages 598-606.e2
Gastroenterology

Basic—Alimentary Tract
Release of Endogenous Opioids From Duodenal Enteroendocrine Cells Requires Trpm5

https://doi.org/10.1053/j.gastro.2009.02.070Get rights and content

Background & Aims

Enteroendocrine cells, the largest and most diverse population of mammalian endocrine cells, comprise a number of different cell types in the gut mucosa that produce, store, and secrete small molecules, peptides, and/or larger proteins that regulate many aspects of gut physiology. Little is known about less typical endocrine cells in the intestinal mucosa that do not contain secretory granules, such as brush or caveolated cells. We studied a subset of these enteroendocrine cells in duodenum that produce several peptides, including endogenous opioids, and that also express the Trpm5 cation channel.

Methods

We studied expression patterns of Trpm5 and other molecules by immunohistochemical and enzyme-linked immunosorbent assay analyses of intestinal tissues from transgenic mice that express green fluorescent protein from the Trpm5 promoter, as well as wild-type and Trpm5-null mice.

Results

We describe a type of enteroendocrine cell in mouse duodenum that is defined by the presence of Trpm5 and that does not contain typical secretory granules yet expresses endogenous opioids (β-endorphin and Met-enkephalin) and uroguanylin in apical compartments close to the lumen of the gut.

Conclusions

Solitary chemosensory cells that coexpress β-endorphin, Met-enkephalin, uroguanylin, and Trpm5 exist in mouse duodenum. These cells are likely to secrete the bioactive peptides into the intestinal lumen in response to dietary factors; release of the opioid peptides requires the Trpm5 ion channel.

Section snippets

Mice

Transgenic mice expressing enhanced green fluorescent protein (GFP) from a 10-kilobase-long Trpm5 promoter and Trpm5 knockout (KO) mice were described previously.5, 26 Their genetic background is C57Bl/6. Control wild-type (WT) mice were C57Bl/6 obtained from Charles River Laboratories (Wilmington, MA) or bred at Mount Sinai Animal Facility (New York, NY). All animals were kept on a regular mouse chow and maintained according to the Mount Sinai Institutional Animal Care and Use Committee

Trpm5 Expression in Mouse Intestine

Trpm5 expression in intestinal cells was monitored by immunohistochemistry and expression of a GFP transgene faithfully driven in Trpm5-expressing taste cells by the 12-kilobase-long Trpm5 promoter.26 Both methods revealed a large number of scattered Trpm5-expressing cells throughout the entire gut, from stomach to colon. By comparing GFP transgene fluorescence with Trpm5 immunostaining, we determined that all Trpm5-positive GFP-positive gut cells also expressed endogenous Trpm5 protein (Figure

Discussion

In taste cells, the Trpm5 ion channel is indispensable for propagating chemosensory signals to the nervous system. Its main role appears in assisting membrane depolarization in a final step in signal transmission from activation of G-protein–coupled receptors. Mice deficient in Trpm5 are severely affected in their ability to sense sweet, bitter, and umami compounds, tastants that all activate G protein–coupled receptors.6, 7, 34

In this report, we describe solitary chemosensory cells in mouse

Acknowledgments

Z.K. and D.R. contributed equally to this report.

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    Conflicts of interest Dr Margolskee has a personal financial interest in the form of stock ownership in the Redpoint Bio company, receives consulting fees from the Redpoint Bio company, and is an inventor on patents and patent applications that have been licensed to the Redpoint Bio company. The remaining authors disclose no conflicts.

    Funding Supported in part by National Institutes of Health grants DC007399 and DK073248 (to B.M.) and DC03055 (to R.F.M.).

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