Ana San Gabriel

mGluR1 in the fundic glands of rat stomach

l‐glutamate not only confers cognitive discrimination for umami taste in the oral cavity, but also conveys sensory information to vagal afferent fibers in the gastric mucosa. We used RT‐PCR, western blotting, and immunohistochemistry to demonstrate that mGluR1 is located in glandular stomach. Double staining revealed that mGluR1 is found at the apical membrane of chief cells and possibly in parietal cells. Moreover, a diet with 1% l‐glutamate induced changes in the expression of pepsinogen C mRNA in stomach mucosa. These data suggest that mGluR1 is involved in the gastric phase regulation of protein digestion.

Metabotropic glutamate receptor type 1 in taste tissue

l-Glutamate confers cognitive discrimination for umami taste (delicious or savory) and dietary information to the brain through the activation of G protein-coupled receptors in specialized taste receptor cells of the tongue. The taste heterologous receptor T1R1 plus T1R3 is not sufficient to detect umami taste in mice. The lack of T1R3 diminished but did not abolish nerve and behavioral responses in null mice that still contained umami-sensitive taste receptor cells. The remnant umami responses in T1R3 knockout mice indicate that there are also T1R3 independent receptors. Metabotropic glutamate receptor 1 (mGluR1), which is widely expressed throughout the central nervous system and regulates synaptic signaling, is another l-glutamate receptor candidate. It is found within taste buds, although the amount of l-glutamate in the perisynaptic region is in the order of micromol/L, whereas free dietary l-glutamate is in the mmol/L range. We reexamined the expression of one mGluR1 variant with a lower affinity for l-glutamate that is found in fungiform and circumvallate papillae. This taste mGluR1 receptor responds in vitro to the concentration of l-glutamate usually found in foodstuffs.

Amino acid sensing in the gastrointestinal tract

Rapid progress in gastroenterology during the first part of the last century has shown that gastrointestinal (GI) function is regulated by neuroendocrine, paracrine and endocrine signals. However, recent advances in chemical sensing, especially in the last decade, have revealed that free l-amino acids (AA), among other nutrients, play a critical role in modifying exocrine and endocrine secretion, modulating protein digestion, metabolism and nutrient utilization, and supporting the integrity and defense of the GI mucosa. Many of the mechanisms by which AAs elicit these functions in the GI has been linked to the traditional concept of hormone release and nervous system activation. But most these effects are not direct. AAs appear to function by binding to a chemical communication system such as G protein-coupled receptors (GPCRs) that activate signaling pathways. These intracellular signals, although their molecular bases are not completely elucidated yet, are the ones responsible for the neuronal activity and release of hormones that in turn regulate GI functions. This review aims to describe the distribution of the known GPCRs from the class 3 superfamily that bind to different kinds of AA, especially from the oropharyngeal cavity to the stomach, what kind of taste qualities they elicit, such as umami, bitter or sweet, and their activity in the GI tract.

The calcium-sensing receptor in taste tissue

Calcium is an essential nutrient that induces a distinctive taste quality, but the sensing mechanism of calcium in the tongue is poorly understood. A recent study linked calcium to T1R3 receptor. Here, we propose another system for calcium taste involving the extracellular calcium-sensing receptor (CaSR). This G protein-coupled receptor that responds to calcium and magnesium cations is involved in calcium homeostasis regulating parathyroid and kidney functions. In this study, CaSR was found in isolated taste buds from rats and mice. It was expressed in a subset of cells in circumvallate and foliate papillae, with fewer cells in the fungiform papillae. This is the first evidence in mammals that locates CaSR in gustatory tissue and provides the basis for better understanding not only calcium taste but also the taste of multiple CaSR agonists.

Free amino acid content in infant formulas

Purpose – Infant formula is the sole nutrition and food source for many infants. Information on the free amino acid (FAA) content of formulas, particularly those that are protein hydrolysate based, is limited, despite emerging evidence for the role of FAAs in regulating eating behaviour. The purpose of this paper is to measure levels of essential, semi‐essential, and nonessential FAAs in commercially available infant formulas to provide a foundation for future research examining the influence of FAAs on infant development.Design/methodology/approach – Using an automatic amino acid analyzer, we measured the concentrations of FAAs in four types of formula: two cow milk (CMF); three soy protein (SPF); and three protein hydrolysate (PHF), one of which was a partial hydrolysate (pPHF) and two of which were extensive hydrolysate (ePHF).Findings – It was found that the amount and number of FAAs varied significantly across formula types: for CMF, total FAAs ranged from 523‐864 μmol/L, with taurine being the most ...

Production of free glutamate in milk requires the leucine transporter LAT1.

The concentration of free glutamate (Glu) in rats milk is ∼10 times higher than that in plasma. Previous work has shown that mammary tissue actively transports circulatory leucine (Leu), which is transaminated to synthesize other amino acids such as Glu and aspartate (Asp). To investigate the molecular basis of Leu transport and its conversion into Glu in the mammary gland, we characterized the expression of Leu transporters and [(3)H]Leu uptake in rat mammary cells. Gene expression analysis indicated that mammary cells express two Leu transporters, LAT1 and LAT2, with LAT1 being more abundant than LAT2. This transport system is sodium independent and transports large neutral amino acids. The Leu transport system in isolated rat mammary cells could be specifically blocked by the LAT1 inhibitors 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid (BCH) and triiodothyronine (T3). In organ cultures, Glu secretion was markedly inhibited by these LAT1 inhibitors. Furthermore, the profiles of Leu uptake inhibition by amino acids in mammary cells were similar to those reported for LAT1. In vivo, concentrations of free Glu and Asp increased in milk by oral gavage with Leu at 6, 12, and 18 days of lactation. These results indicate that the main Leu transporter in mammary tissue is LAT1 and the transport of Leu is a limiting factor for the synthesis and release of Glu and Asp into milk. Our studies provide the bases for the molecular mechanism of Leu transport in mammary tissue by LAT1 and its active role on free Glu secretion in milk, which confer umami taste in suckling pups.

M1714 Functional Role of Calcium-Sensing Receptor on Somatostatin Release From Rat Gastric Mucosa

G A A b st ra ct s profiles and examined the effects of 5-HT and GLP-1 on EC and L cells respectively to assess the likelihood of an interactive functional relationship between these neuroendocrine cells. Methods: We used an adenocarcinoma cell line (NCI-H716) as a model for L cells and the KRJ-1 cell line as a model for EC cells. Duodenal mucosa was used to studied hormone release ex vivo. Receptor expression was identified using real-time PCR and western blot. The WST-1 proliferation assay was used to assess cell proliferation in response to exendin-4 (long-acting GLP-1 agonist) and 5HT. 5HT and GLP1 secretion was assessed (ELISA) and signaling pathways investigated (cAMP ELISA and MAPK phosphorylation). Results: EC cells express GLP receptor mRNA and protein. L cells express 5HT1A and 5HT2A receptor mRNA and protein but not 5HT2B, 5HT2C, or 5HT3A mRNA. Exendin4 promoted proliferation of EC cells and L cells at high concentration (10uM). 5HT has no effect on proliferation of L cells. Exendin-4 decreased 5HT secretion from EC cells (25%35% decrease, p=0.02) with an ~IC50=1nM. This was associated with a 25-45% (p<0.05) decrease in intracellular cAMP and MAPK phosphorylation and could be reversed by the GLP1 antagonist (GLP8-38). Addition of exendin-4 to isolated duodenal tissue also inhibited serotonin release (30-40% decrease, p=0.024). 5HT treatment has no significant effect on GLP-1 secretion from L cells. Conclusion: GLP-1 is a proliferative agent for neoplastic EC cells at micromolar concentrations. In contrast, at physiological (nanomolar) concentrations, GLP1 inhibits EC cell 5HT secretion via cAMP/MAPK-mediated pathways. Given the central role of EC cells in regulating GI function (motility, secretion, nociception), it is possible that the L cell plays a key up-stream regulatory role in these phenomenon. These results also suggest that EC cell proliferation is not an independent event and that other neuroendocrine cells may regulate EC function and play a role in NET development.

The Role of the Japanese Traditional Diet in Healthy and Sustainable Dietary Patterns around the World

As incomes steadily increase globally, traditional diets have been displaced by diets that are usually animal-based with a high content of “empty calories” or refined sugars, refined fats, and alcohol. Dietary transition coupled with the expansion of urbanization and lower physical activity have been linked to the global growth in the prevalence of obesity, overweight and life style-related non-communicable diseases. The challenge is in how to reverse the trend of high consumption of less healthy food by more healthful and more environmentally sustainable diets. The increasing recognition that each individual has specific needs depending on age, metabolic condition, and genetic profile adds complexity to general nutritional considerations. If we were to promote the consumption of low-energy and low salt but nutritious diets, taste becomes a relevant food quality. The Japanese traditional diet (Washoku), which is characterized by high consumption of fish and soybean products and low consumption of animal fat and meat, relies on the effective use of umami taste to enhance palatability. There may be a link between Washoku and the longevity of the people in Japan. Thus Washoku and umami may be valuable tools to support healthy eating.

Appetite: Inhibiting Properties of Proteins

Diets rich in proteins promote long-term body weight loss by increasing satiation with a greater effect than carbohydrates and fats. l-glutamate that imparts umami or savory taste is thought to be a signal for protein consumption and may promote the satiating effect of proteins. The ingestion of proteins results in the release of anorexigenic gut neuropeptides such as cholecystokinin, glucagon peptide 1, and peptide YY that transmit satiety signals to the brain steam via vagal afferent pathways. Gut neuropeptides come from enteroendocrine cells disseminated throughout the alimentary canal. They express chemosensing receptors in the apical membrane that can detect the presence of peptone and single amino acids in the luminal content. High-protein diets convey stronger AA-satiating signals to the brainstem and arcuate nucleus. They also reduce hedonic responses in the reward system. This chapter reviews the gustatory perception of single amino acids in the mouth and their distribution of AA sensors in the gastrointestinal tract including a short overview on their contribution in the integration of protein-satiety signals in the brain.

W1553 Glutamate Reduces Helicobacter pylori-Induced Gastric Atrophy in Rodents - Possible Involvement of Chief Cell Protection via Glutamate Metabolism-

The pH of the alkaline microclimate overlying the duodenal enterocyte brush border is regulated by an ecto-purinergic signaling system consisting of intestinal alkaline phosphatase (IAP), extracellular ATP and P2Y receptors. This system regulates the rate of duodenal bicarbonate secretion (DBS). IAP inhibition increases DBS and non-lytic ATP release into the lumen, the mechanism of which has not been clarified. Ecto-F1F0-ATP synthase has been localized to the plasma membrane of several non-epithelial cell types. We hypothesized that ecto-ATP synthase generates extracellular ATP, regulating DBS as part of the ectopurinergic signaling system. We measured DBS with flow-through pH and CO2 electrodes with the perfusate ATP content measured by luciferin-luciferase bioassay. We tested the effect of perfusion of the competitive AP inhibitor glycerol phosphate (GP, 10 mM) with or without the addition of ATP synthase inhibitors oligomycin (Om, 5 μg/ml), piceatannol (Pic, 20 μM) or resveratorol (Res, 20 μM), or the mitochondrial uncoupler carbonyl cyanide 3-chlorophenylhydrazone (CCCP, 1 μM) on DBS and ATP output. GP increased DBS and ATP output. Pic or Res inhibited GP-induced augmented DBS and ATP output. GP, or Pic or Res with GP had no effect on LDH release, confirming the absence of lytic cellular injury. Om or CCCP had a lesser effect on GP-induced DBS, but inhibited GP-induced ATP output accompanied by increased LDH release, consistent with cellular injury. Furthermore, α and β subunits of F1 complex of ATP synthase were immunolocalized to the brush border membranes (α β) in the lamina propria mucosa. Furthermore, phosphate buffer saline (pH 7.0, 10 mM) increased ATP output, suggesting that excess supply of inorganic phosphate (Pi) may enhance ATP synthesis and/or inhibit ATP degradation. Luminal ATP release unmasked by IAP inhibition is dependent on extracellular ATP synthesis, consistent with the presence of ecto-ATP synthase on the brush border. Extracellular ATP synthesis and ATP degradation by IAPmay coordinately regulate ATP-P2Y signaling for DBS as part of a novel ecto-purinergic signaling system.