Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are the major anions in the large intestinal lumen. They are produced from dietary fiber by bacterial fermentation and are known to have a variety of physiological and pathophysiological effects on the intestine. In the present study, we investigated the expression of the SCFA receptor, GPR43, in the rat distal ileum and colon. Expression of GPR43 was detected by reverse transcriptase/polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemistry. mRNA for GPR43 was detected, by RT-PCR, in extracts of the whole wall and separated mucosa from the ileum and colon and from muscle plus submucosa from the ileum, but not from muscle plus submucosa preparations from the colon. We raised a rabbit antiserum against a synthesized fragment of rat GPR43; this was specific for rat GPR43. GPR43 protein was detected by Western blot analysis in extracts of whole wall and separated mucosa, but not in muscle plus submucosa extracts. By immunohistochemistry, GPR43 immunoreactivity was localized to enteroendocrine cells expressing peptide YY (PYY), whereas 5-hydroxytryptamine (5-HT)-immunoreactive (IR) enteroendocrine cells were not immunoreactive for GPR43. Mast cells of the lamina propria expressing 5-HT were also GPR43-IR. The results of the present study suggest that the PYY-containing enteroendocrine cells and 5-HT-containing mucosal mast cells sense SCFAs via the GPR43 receptor. This is consistent with physiological data showing that SCFAs stimulate the release of PYY and 5-HT from the ileum and colon.

Short-chain fatty acids (SCFAs), 2-4 carbon monocarboxylates including acetate, propionate and butyrate, are known to have a variety of physiological and pathophysiological effects on the intestine. Previously, we reported that the SCFA receptor, G-protein coupled receptor 43 (GPR43), is expressed by enteroendocrine and mucosal mast cells in the rat intestine. In the present study, expression and localization of GPR43 were investigated in the human large intestine. Gene and protein expression of GPR43 in the human ascending colon was analyzed by reverse transcriptase/polymerase chain reaction and Western blotting, respectively. In addition, localization of GPR43 was investigated by immunohistochemistry. In RT-PCR analysis, GPR43 mRNA was detected in whole wall mRNA samples. Western blotting analysis revealed the expression of GPR43 protein in whole wall and scraped mucosa protein samples, but not in muscle or submucosa. GPR43 immunoreactivity was observed in the intracellularly in enterocytes and in the peptide YY-immunoreactive enteroendocrine cells. These results indicate that the short chain fatty acid receptor, GPR43 is expressed by enteroendocrine L cells containing peptide YY in the human large intestine.

Short-chain fatty acids (SCFAs), including acetate, propionate and butyrate, are the most commonly found anions found in the monogastric mammalian large intestine, and are known to have a variety of physiological and pathophysiological effects on the gastrointestinal tract. We investigated the protein and mRNA expression levels of GPR41, a possible G protein coupled receptor for SCFA, using Western blot analysis and reverse transcriptase-polymerase chain reaction. We found that GPR41 protein and mRNA are expressed in human colonic mucosa. Immunohistochemistry for GPR41 showed that mucosal GPR41 protein is localized in cytoplasm of enterocytes and enteroendocrine cells. Moreover, GPR41-immunoreactive endocrine cells contained peptide YY but not serotonin or GPR43. The cellular population of GPR41 (0.01 ± 0.01 cells/crypt) was much smaller than that of GPR43 (0.33 ± 0.01 cells/crypt) in the human colon. However, the potency order of SCFA-induced phasic contraction of colonic smooth muscle that we previously reported is consistent with GPR41 (propionate ≧ butyrate > acetate) but not GPR43 (propionate = butyrate = acetate). Therefore, the present study suggests that GPR41 expressed in human colonic mucosa may function as a sensor for luminal SCFAs.Short-chain fatty acids (SCFA) are a major anion present in the large intestinal lumen of monogastric mammals including humans. SCFAs are produced during anaerobic bacterial fermentation of unabsorbed carbohydrates and dietary fibers. The concentration of SCFAs in human feces is reported to be approximately 100 mM, and are primarily comprised of acetate, propionate, and butyrate. Molar ratios of SCFAs in human fecal content are 50-60, 15-20, and 10-20 for acetate, propionate, and butyrate respectively (3, 22). Through absorption and metabolism of SCFAs, the host is able to salvage energy from food not digested in the upper intestine. Furthermore, luminal SCFAs have various physiological and pathophysiological effects in the gastrointestinal (GI) tract (4,10,17,19). In our previous studies, we demonstrated that SCFAs evoke two different effects on rat colonic smooth muscle in vitro (13)(14)(15). In the early phase, propionate and butyrate induced concentrationdependent phasic contractions in circular and longitudinal muscle, but acetate had no such effect (13-15). In the late phase, propionate induced a concentration-dependent increase in frequency of spontaneous contractions in circular (13) and longitudinal muscle (15), but butyrate did not affect the frequency of spontaneous longitudinal muscle contractions (15). On the other hand, acetate induced a

Short-chain fatty acids (SCFA) are monocarboxylates produced by bacterial fermentation that play a crucial role in maintaining homeostasis in the large intestine. Two major transporters for SCFA, monocarboxylate transporter (MCT) and slc5a8 (or SMCT), exist in the digestive tract. The present histochemical study using in situ hybridization and immunohistochemistry revealed the distribution and subcellular localization of the MCT family in the digestive tract of mice, rats, and humans, comparing these with that of slc5a8. The expression of mucosal MCT1 in the mouse and rat was most intense in the cecum, followed by the colon, but low in the stomach and small intestine. Among other MCT subtypes, only MCT2 was detected in the parietal cell region of the gastric mucosa. Slc5a8 had predominant expression sites in the distal half of the large bowel and in the most terminal ileum. The mucosal MCT1 was localized in the basolateral membrane of enterocytes, while slc5a8 was restricted to the apical cell membrane, suggesting the involvement of slc5a8 in the uptake of luminal SCFA, and of MCT1 in the effl ux of SCFA and monocarboxylate metabolites towards blood circulation. The large intestine expressed both types of the transporter, but their distribution patterns differed along the longitudinal axis of the intestine and along the perpendicular axis of the mucosa.Plant-derived dietary fi ber and undigested carbohydrates are fermented by bacterial microfl ora in the large intestine and produce acetate, propionate, and butyrate, collectively called short-chain fatty acids (SCFA). These are monocarboxylates which contain less than fi ve carbon atoms: acetate has two carbons, propionate has three, and butyrate has four. The SCFA in the bowel lumen have some effects on the intestinal wall, including the stimulation of colonic blood fl ow and of fl uid and electrolyte uptake (30). Butyrate also functions as an energy source of epithelial cells in the large intestine and promotes differentiation of the cells (2, 21) while suppressing the proliferation of tumor cells by the induction of apoptosis (6). Thus, direct and indirect intraluminal supplementation of butyrate maintains and strengthens the epithelial integrity to suppress mucosal damage such as ulcerative colitis (15,16,19,27). At least 60% of the SCFA uptake in the large intestine occurs by simple diffusion of the unionized form across the cell membrane; the remainder occurs by the active cellular uptake of ionized SCFA involving co-transport of inorganic protons, such as Na + , K + , and H + (7). As a transporter of SCFA, monocarboxylate transporter (MCT)-1 was fi rst identifi ed and localized in intestinal epithelial cells as well as the heart, kidney, and epididymis (9). MCT1 can transport lactate, pyruvate, and SCFA in a H + -dependent manner. The

Background: Gut microbiota affects host homeostasis and dysbiosis causes host diseases. Therefore, uncovering the sensing mechanism of bacterial metabolites such as short-chain fatty acid (SCFA) may help us to understand the host-microbiota interaction both in physiological and nonphysiological conditions. Summary: The colonic lumen is continually exposed to many kinds of chemicals, including beneficial and harmful compounds that are produced by gut microbiota in addition to ingested nutrients. In the mammalian colon SCFAs such as acetate, propionate and butyrate are produced by bacterial fermentation and reach about 100 mM under physiological conditions. In this decade, SCFA receptor genes and their expression in the intestine have been identified as free fatty acid receptor (FFA)2 and FFA3. The FFAs are located in colonic enteroendocrine L cells producing and releasing an insulinotropic hormone, glucagon-like peptide-1 (GLP-1), and an anorectic hormone, peptide YY. Recent in vivo and in vitro studies suggest that SCFAs stimulate gut hormone secretion. Therefore, the SCFA-FFA signal is likely to be important for gut physiological functions. Key Message: Colonic epithelial cells express chemical receptors that detect the luminal contents, particularly bacterial metabolites, and may be involved in the host's energy metabolism via GLP-1 release, as well as the mucosal defense system.

Taste transduction molecules, such as Galpha(gust), and taste receptor families for bitter [taste receptor type 2 (T2R)], sweet, and umami, have previously been identified in taste buds and the gastrointestinal (GI) tract; however, their physiological functions in GI tissues are still unclear. Here, we investigated the physiological function and expression of T2R in human and rat large intestine using various physiological and molecular biological techniques. To study the physiological function of T2R, the effect of a bitter compound, 6-n-propyl-2-thiouracil (6-PTU), on transepithelial ion transport was investigated using the Ussing chamber technique. In mucosal-submucosal preparations, mucosal 6-PTU evoked Cl(-) and HCO(3)(-) secretions in a concentration-dependent manner. In rat middle colon, levels of 6-PTU-evoked anion secretion were higher than in distal colon, but there was no such difference in human large intestine. The response to 6-PTU was greatly reduced by piroxicam, but not by tetrodotoxin. Additionally, prostaglandin E(2) concentration-dependently potentiated the response to 6-PTU. Transcripts of multiple T2Rs (putative 6-PTU receptors) were detected in both human and rat colonic mucosa by RT-PCR. In conclusion, these results suggest that the T2R ligand, 6-PTU, evokes anion secretion, and such response is regulated by prostaglandins. This luminal bitter sensing mechanism may be important for host defense in the GI tract.

Glucagon-like peptide 1 (GLP-1) is a multifunctional hormone in glucose metabolism and intestinal function released by enteroendocrine L-cells. The plasma concentration of GLP-1 is increased by indigestible carbohydrates and luminal infusion of short-chain fatty acids (SCFAs). However, the triggers and modulators of the GLP-1 release remain unclear. We hypothesized that SCFAs produced by bacterial fermentation are involved in enteroendocrine cell proliferation and hormone release through free fatty acid receptor 2 (FFA2, also known as FFAR2 or GPR43) in the large intestine. Fructo-oligosaccharide (Fructo-OS), fermentable indigestible carbohydrate, was used as a source of SCFAs. Rats were fed an indigestible-carbohydrate-free diet (control) or a 5% Fructo-OS-containing diet for 28 days. FFA2-, GLP-1-, and 5-hydroxytryptamine (5-HT)-positive enteroendocrine cells were quantified immunohistochemically in the colon, cecum, and terminal ileum. The same analysis was performed in surgical specimens from human lower intestine. The coexpression of FFA2 with GLP-1 was investigated both in rats and humans. Fructo-OS supplementation in rats increased the densities of FFA2-positive enteroendocrine cells in rat proximal colon, by over two-fold, relative to control, in parallel with GLP-1-containing L-cells. The segmental distributions of these cells in human were similar to rats fed the control diet. The FFA2-positive enteroendocrine cells were GLP-1-containing L-cells, but not 5-HT-containing EC cells, in both human and rat colon and terminal ileum. Fermentable indigestible carbohydrate increases the number of FFA2-positive L-cells in the proximal colon. FFA2 activation by SCFAs might be an important trigger for produce and release GLP-1 by enteroendocrine L-cells in the lower intestine.

Short-chain fatty acids (SCFAs), including propionate, butyrate and acetate, are fermentation products of carbohydrates in the colon. We investigated the contractile effects of SCFAs on the rat distal colon. Mechanical activity of the circular muscle in strip preparations was recorded in vitro. Propionate and butyrate concentration-dependently (10 micromol L(-1)-10 mmol L(-1)) induced rapid, large amplitude phasic contractions (the first phase) followed by tonic contractions (the second phase). Acetate itself had no effect on muscle activity, although preincubation with acetate attenuated both phases of the propionate-induced response. The propionate-induced phasic contraction was attenuated by atropine, tetrodotoxin and the 5-HT4 receptor antagonist SB-204070. The propionate-induced tonic contraction was attenuated by the cyclo-oxygenase inhibitor piroxicam. Antagonists of 5-HT1A, 5-HT2A and 5-HT3 receptors had no effect on the responses. Propionate-induced responses were not observed in mucosa-free preparations. These results suggest that propionate acts on receptors in the mucosa causing the release of 5-HT from enterochromaffin cells. 5-HT acts through 5-HT4 receptors on the endings of intrinsic primary afferent neurones that in turn activate cholinergic motor neurones that contract the circular muscle. Propionate also causes tonic contraction, via prostaglandin release, in the rat distal colon.