Phenylalanine and tryptophan stimulate gastrin and somatostatin secretion and H+-K+-ATPase activity in pigs through calcium-sensing receptor

Gastric acid secretion is activated by two distinct pathways: a neuronal pathway via the vagus nerve and release of acetylcholine and an endocrine pathway involving gastrin and histamine. Recently, we demonstrated that activation of H+-K+-ATPase activity in parietal cells in freshly isolated rat gastric glands is modulated by the calcium-sensing receptor (CaSR). Here, we investigated if the CaSR is functionally expressed in freshly isolated gastric glands from human patients undergoing surgery and if the CaSR is influencing histamine-induced activation of H+-K+-ATPase activity. In tissue samples obtained from patients, immunohistochemistry demonstrated the expression in parietal cells of both subunits of gastric H+-K+-ATPase and the CaSR. Functional experiments using the pH-sensitive dye 2′,7′-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein and measurement of intracellular pH changes allowed us to estimate the activity of H+-K+-ATPase in single freshly isolated human gastric glands. Under control conditions, H+-K+-ATPase activity was stimulated by histamine (100 μM) and inhibited by omeprazole (100 μM). Reduction of the extracellular divalent cation concentration (0 Mg2+, 100 μM Ca2+) inactivated the CaSR and reduced histamine-induced activation of H+-K+-ATPase activity. In contrast, activation of the CaSR with the trivalent cation Gd3+ caused activation of omeprazole-sensitive H+-K+-ATPase activity even in the absence of histamine and under conditions of low extracellular divalent cations. This stimulation was not due to release of histamine from neighbouring enterochromaffin-like cells as the stimulation persisted in the presence of the H2 receptor antagonist cimetidine (100 μM). Furthermore, intracellular calcium measurements with fura-2 and fluo-4 showed that activation of the CaSR by Gd3+ led to a sustained increase in intracellular Ca2+ even under conditions of low extracellular divalent cations. These experiments demonstrate the presence of a functional CaSR in the human stomach and show that this receptor may modulate the activity of acid-secreting H+-K+-ATPase in parietal cells. Furthermore, our results show the viability of freshly isolated human gastric glands and may allow the use of this preparation for experiments investigating the physiological regulation and properties of human gastric glands in vitro.

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l-Type amino acids stimulate gastric acid secretion by activation of the calcium-sensing receptor in parietal cells

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00096.2005 ◽

2005 ◽

Vol 289 (4) ◽

pp. G664-G669 ◽

Cited By ~ 71

Author(s):

Stephanie M. Busque ◽

Jane E. Kerstetter ◽

John P. Geibel ◽

Karl Insogna

Keyword(s):

Amino Acids ◽

Atpase Activity ◽

Acid Secretion ◽

Ex Vivo ◽

Parietal Cells ◽

Secretory Cells ◽

Calcium Sensing Receptor ◽

Gastric Glands ◽

Calcium Sensing ◽

System L

Parietal cells are the primary acid secretory cells of the stomach. We have previously shown that activation of the calcium-sensing receptor (CaSR) by divalent (Ca2+) or trivalent (Gd3+) ions stimulates acid production in the absence of secretagogues by increasing H+,K+-ATPase activity. When overexpressed in HEK-293 cells, the CaSR can be allosterically activated by l-amino acids in the presence of physiological concentrations of extracellular Ca2+ (Cao2+; 1.5–2.5 mM). To determine whether the endogenously expressed parietal cell CaSR is allosterically activated by l-amino acids, we examined the effect of the amino acids l-phenylalanine (l-Phe), l-tryptophan, and l-leucine on acid secretion. In ex vivo whole stomach preparations, exposure to l-Phe resulted in gastric luminal pH significantly lower than controls. Studies using d-Phe (inactive isomer) failed to elicit a response on gastric pH. H+-K+-ATPase activity was monitored by measuring the intracellular pH (pHi) of individual parietal cells in isolated rat gastric glands and calculating the rate of H+ extrusion. We demonstrated that increasing Cao2+ in the absence of secretagogues caused a dose-dependent increase in H+ extrusion. These effects were amplified by the addition of amino acids at various Cao2+ concentrations. Blocking the histamine-2 receptor with cimetidine or inhibiting system l-amino acid transport with 2-amino-2-norbornane-carboxylic acid did not affect the rate of H+ extrusion in the presence of l-Phe. These data support the conclusion that amino acids, in conjunction with a physiological Cao2+ concentration, can induce acid secretion independent of hormonal stimulation via allosteric activation of the stomach CaSR.

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Modulations in extracellular calcium lead to H+-ATPase-dependent acid secretion: a clarification of PPI failure

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00132.2017 ◽

2018 ◽

Vol 315 (1) ◽

pp. G36-G42 ◽

Cited By ~ 2

Author(s):

Alice Miriam Kitay ◽

Marie-Therese Schneebacher ◽

Anne Schmitt ◽

Katharina Heschl ◽

Sascha Kopic ◽

...

Keyword(s):

Atpase Activity ◽

Acid Secretion ◽

Parietal Cell ◽

Proton Pump ◽

Extracellular Calcium ◽

Calcium Sensing Receptor ◽

Gastric Parietal Cell ◽

Blood Calcium ◽

Calcium Sensing ◽

Sodium And Potassium

The H+,K+-ATPase was identified as the primary proton secretory pathway in the gastric parietal cell and is the pharmacological target of agents suppressing acid secretion. Recently, we identified a second acid secretory protein expressed in the parietal cell, the vacuolar H+-ATPase (V-type ATPase). The aim of the present study was to further characterize H+-ATPase activation by modulations in extracellular calcium via the calcium sensing receptor (CaSR). Isolated gastric glands were loaded with the pH indicator dye BCECF-AM [2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester] to measure intracellular pH. Experiments were conducted in the absence of sodium and potassium to monitor H+-ATPase-specific transport activity. CaSR was activated with the calcimimetic R568 (400 nM) and/or by modulations in extracellular Ca2+. Elevation in calcium concentrations increased proton extrusion from the gastric parietal cell. Allosteric modification of the CaSR via R568 and calcium increased vacuolar H+-ATPase activity significantly (ΔpH/minlowCa2+(0.1mM) = 0.001 ± 0.001, ΔpH/minnormalCa2+(1.0mM) = 0.033 ± 0.004, ΔpH/minhighCa2+(5.0mM) = 0.051 ± 0.005). Carbachol significantly suppressed calcium-induced gastric acid secretion via the H+-ATPase under sodium- and potassium-free conditions. We conclude that the V-type H+-ATPase is tightly linked to CaSR activation. We observed that proton pump inhibitor (PPI) exposure does not modulate H+-ATPase activity. This elevated blood calcium activation of the H+-ATPase could provide an explanation for recurrent reflux symptoms while taking a PPI therapy. NEW & NOTEWORTHY This study emphasizes the role of the H+-ATPase in acid secretion. We further demonstrate the modification of this proton excretion pathway by extracellular calcium and the activation of the calcium sensing receptor CaSR. The novelty of this paper is based on the modulation of the H+-ATPase via both extracellular Ca (activation) and the classical secretagogues histamine and carbachol (inactivation). Both activation and inactivation of this proton pump are independent of PPI modulation.

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Calcium-sensing receptor (CaSR) modulates vacuolar H+-ATPase activity in a cell model of proximal tubule

Clinical and Experimental Nephrology ◽

10.1007/s10157-018-1613-z ◽

2018 ◽

Vol 22 (6) ◽

pp. 1258-1265

Author(s):

Priscilla Marys Costa Dos Santos ◽

Deividi Amaral ◽

Ana Lucia Tararthuch ◽

Ricardo Fernandez

Keyword(s):

Atpase Activity ◽

Proximal Tubule ◽

Cell Model ◽

Calcium Sensing Receptor ◽

Calcium Sensing ◽

A Cell

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Stimulation of calcium-sensing receptor increases biochemical H+-ATPase activity in mouse cortex and outer medullary regions

Canadian Journal of Physiology and Pharmacology ◽

10.1139/cjpp-2013-0256 ◽

2014 ◽

Vol 92 (3) ◽

pp. 181-188 ◽

Cited By ~ 7

Author(s):

Fernando Casare ◽

Daiane Milan ◽

Ricardo Fernandez

Keyword(s):

Atpase Activity ◽

Intracellular Signaling ◽

Calcium Sensing Receptor ◽

Proton Extrusion ◽

Biochemical Activity ◽

Outer Medulla ◽

Calcium Sensing ◽

Mouse Cortex ◽

Dose Dependent ◽

Stimulation Of

The aim of this project was to investigate the interaction between the calcium-sensing receptor (CaSR) and proton extrusion by the V-ATPase and gastric-like isoform of the H+/K+-ATPase in the mouse nephron. Biochemical activity of H+- ATPases was analysed using a partially purified membrane fraction of mouse cortex and outer medullary region. The V-ATPase activity (sensitive to 10−7 mol·L−1 bafilomycin) from the cortical and outer medullary region was significantly stimulated by increasing the [Formula: see text] (outside Ca2+), in a dose-dependent pattern. Gastric H+/K+-ATPase activity (sensitive to 10−5 mol·L−1 Schering 28080) was also sensitive to changes in [Formula: see text] levels. A significant increase in V-ATPase activity was also observed when CaSR was stimulated with agonists such as 300 μmol·L−1 Gd3+ and 200 μmol·L−1 neomycin, both in the cortex and outer medulla. The cortical and outer medullary gastric H+/K+-ATPase activity was also stimulated by Gd3+ and neomycin. Finally, cortical V-ATPase activity was significantly stimulated by 10−9 mol·L−1 angiotensin II, and the stimulation of CaSR in the presence of angiotensin significantly enhanced this effect, suggesting that an interaction in the intracellular signaling pathways is involved. In summary, CaSR stimulation enhances the biochemical activity of V-ATPase and gastric H+/K+-ATPase in both the cortical and outer medullary region of mouse kidney.

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