Gastric Serotonin Biosynthesis and Its Functional Role in L-Arginine-Induced Gastric Proton Secretion

Abstract

Among mammals, serotonin is predominantly found in the gastrointestinal tract, where it has been shown to participate in pathway-regulating satiation. For the stomach, vascular serotonin release induced by gastric distension is thought to chiefly contribute to satiation after food intake. However, little information is available on the capability of gastric cells to synthesize, release and respond to serotonin by functional changes of mechanisms regulating gastric acid secretion. We investigated whether human gastric cells are capable of serotonin synthesis and release. First, HGT-1 cells, derived from a human adenocarcinoma of the stomach, and human stomach specimens were immunostained positive for serotonin. In HGT-1 cells, incubation with the tryptophan hydroxylase inhibitor p-chlorophenylalanine reduced the mean serotonin-induced fluorescence signal intensity by 27%. Serotonin release of 147 ± 18%, compared to control HGT-1 cells (set to 100%) was demonstrated after treatment with 30 mM of the satiating amino acid L-Arg. Granisetron, a 5-HT3 receptor antagonist, reduced this L-Arg-induced serotonin release, as well as L-Arg-induced proton secretion. Similarly to the in vitro experiment, human antrum samples released serotonin upon incubation with 10 mM L-Arg. Overall, our data suggest that human parietal cells in culture, as well as from the gastric antrum, synthesize serotonin and release it after treatment with L-Arg via an HTR3-related mechanism. Moreover, we suggest not only gastric distension but also gastric acid secretion to result in peripheral serotonin release.

Bitter Peptides YFYPEL, VAPFPEVF, and YQEPVLGPVRGPFPIIV, Released during Gastric Digestion of Casein, Stimulate Mechanisms of Gastric Acid Secretion via Bitter Taste Receptors TAS2R16 and TAS2R38

“…For all five selected peptides, a significant hormetic concentration-dependent influence on the secretory activity was found. Holik et al showed a hormetic dose–response when HGT-1 cells were incubated with l -arginine. HGT-1 cells released more serotonin when treated with lower l -arginine concentrations (10 mM) than with higher l -arginine concentrations (50 mM).…”

The SLC26A9 inhibitor S9‐A13 provides no evidence for a role of SLC26A9 in airway chloride secretion but suggests a contribution to regulation of ASL pH and gastric proton secretion

“…The cells were expanded and fully differentiated as previously described 22 . The human gastric tumor cell line HGT‐1 was cultured as described earlier 23 …”

“…Proton secretory activity and corresponding data analysis were conducted by means of the pH‐sensitive fluorescence dye 1,5 carboxy‐seminaphto‐rhodafluor acetoxymethylester (SNARF‐1‐AM; Life Technologies), as described previously 23 …”

Reducing the Bitter Taste of Pharmaceuticals Using Cell-Based Identification of Bitter-Masking Compounds

“…The impact of the evaluated compounds on cell viability was assessed using the tetrazole MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reagent. Cells were cultivated in a 96-well plate at a density of 10,000–100,000 viable cells per well and settled for 24–72 h. The assay was applied as previously explained [ 20 ]. Cell viability was determined relative to medium-only treated control cells (untreated controls = 100%).…”

“…Moreover, high signal-to-noise ratios and the need to precisely control external CO 2 levels in order to prevent long time alkalization of the extracellular pH have been observed, particularly when using the standard extracellular medium DMEM which relies on the HCO 3 − /CO 2 buffer system for regulating extracellular pH. In one of our recent works, we used KREBS-Ringer HEPES buffer instead of the cell culture medium DMEM [ 17 ] in order to directly compare results from a serotonin-release assay with those of the proton secretion assay in HGT-1 cells [ 20 ].…”