Regulation of Ion Transport in the Intestine by Free Fatty Acid Receptor 2 and 3: Possible Involvement of the Diffuse Chemosensory System.

Atsukazu Kuwahara,Yoshinori Marunaka,Toshio Inui,Yuko Kuwahara

doi:10.3390/ijms19030735

Abstract

The diffuse chemosensory system (DCS) is well developed in the apparatuses of endodermal origin like gastrointestinal (GI) tract. The primary function of the GI tract is the extraction of nutrients from the diet. Therefore, the GI tract must possess an efficient surveillance system that continuously monitors the luminal contents for beneficial or harmful compounds. Recent studies have shown that specialized cells in the intestinal lining can sense changes in the luminal content. The chemosensory cells in the GI tract belong to the DCS which consists of enteroendocrine and related cells. These cells initiate various important local and remote reflexes. Although neural and hormonal involvements in ion transport in the GI tract are well documented, involvement of the DCS in the regulation of intestinal ion transport is much less understood. Since activation of luminal chemosensory receptors is a primary signal that elicits changes in intestinal ion transport and motility and failure of the system causes dysfunctions in host homeostasis, as well as functional GI disorders, study of the regulation of GI function by the DCS has become increasingly important. This review discusses the role of the DCS in epithelial ion transport, with particular emphasis on the involvement of free fatty acid receptor 2 (FFA2) and free fatty acid receptor 3 (FFA3).

Highlights

The primary function of the gastrointestinal (GI) tract is obtaining energy sources from the diet as nutrients
One such mechanism is the ability to flush out harmful substances via fluid secretion, mainly Cl− secretion. In addition to such a defense mechanism, mild fluid secretion is important to provide appropriate luminal fluidity for commensal bacteria and flush out the harmful substances derived from bacteria and other toxins to maintain a niche of commensal bacteria
We summarize our current knowledge of diffuse chemosensory system (DCS) in the GI tract and discuss possible involvement of this system in the regulation of electrolyte transport stimulated by gut microbiota metabolites, short-chain fatty acids (SCFAs) through free fatty acid receptor 2 (FFA2) and free fatty acid receptor 3 (FFA3) activation

Summary

Introduction

The primary function of the gastrointestinal (GI) tract is obtaining energy sources from the diet as nutrients. Host–microbiota interaction occurs along mucosal surfaces in the intestine of the host and, in the gut, host-defense mechanisms operate to maintain a healthy gut One such mechanism is the ability to flush out harmful substances via fluid secretion, mainly Cl− secretion. In the GI tract, nutrients and microbial metabolites are continuously sensed by chemosensory receptors which are analogs of taste receptors in the tongue [9,10,11] These chemosensory receptors in the stomach and intestine do not trigger taste sensations, such chemical detection elicits appropriate metabolic responses in the host. We discuss the possible involvement of DCS in ion transport stimulated by FFA2 and FFA3 based on our original studies

Diffuse Chemosensory System

Enteroendocrine Cell

Brush Cells

FFA Receptors in the Intestine

Duodenum

Conclusions