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

Abstract

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 Ca. 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/min = 0.001 ± 0.001, ΔpH/min = 0.033 ± 0.004, ΔpH/min = 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.

International Union of Basic and Clinical Pharmacology. CVIII. Calcium-Sensing Receptor Nomenclature, Pharmacology, and Function

“…These effects were potentiated by L-but not D-amino acids, implicating the CaSR (Busque et al, 2005). The function of the recently identified acid secretory protein, vacuolar H + -ATPase, in parietal cells is also dependent on CaSR activity (Kitay et al, 2018).…”

Induction of Secretagogue Independent Gastric Acid Secretion via a Novel Aspirin-Activated Pathway

“…Despite all of these advantages, aspirin has in certain cases been shown to have severe adverse effects such as abdominal pain, dyspepsia, nausea, vomiting, and allergies (Baron et al, 2013). In the stomach, aspirin can be responsible for severe damage to the mucosa within the GI tract, leading to an increased risk of ulcer formation (Serebruany et al, 2005; Kitay et al, 2018) and raising the number of major gastric bleeding events by more than 50% in patients taking low-dose aspirin (Lanas et al, 2011). The inhibition of prostaglandin synthesis has been thought to be the primary reason for these gastrointestinal adverse effects (Shim and Kim, 2016).…”

In Pursuit of the Parietal Cell – An Evolution of Scientific Methodology and Techniques

“…The subsequent recovery of pH i was attributable to H + -ATPase, the only remaining pathway for the extrusions of protons. In addition, we discovered that the activity of the H + -ATPase was upregulated when exposed to calcium (Kitay et al, 2018; Figure 4B).…”

“…However, many patients still suffer from acid hypersecretion. Using the ammonium prepulse technique, our lab identified the vacuolar ATPase as a constitutively active H + -ATPase that is not susceptible to proton pump inhibitors (Kitay et al, 2018). In this experiment, we performed gastric gland dissection to isolate tissue.…”