Effect of ATP on Intracellular pH in Pancreatic Ducts Involves P2X₇ Receptors

Abstract

Pancreatic acini release ATP, which can stimulate HCO₃^--secreting ducts that express purinergic receptors from both P2X and P2Y families. The aim of this study was to investigate whether extracellular ATP affects HCO₃^- or H⁺ transport across the plasma membrane of intralobular ducts, and determine which P2 receptors might be involved. Ducts were obtained from rat pancreas, and the pH sensitive fluorophore BCECF was used to measure pH_i and recovery rates from cellular acidosis induced by ammonium pre-pulses. In order to reveal Na⁺/H⁺ exchange, Cl^-/HCO₃^- exchange or a Na⁺-HCO₃^- cotransport, experiments were performed in solutions with or without bicarbonate buffers (+BIC or –BIC), with amiloride derivative EIPA, or with low extracellular Cl^- concentrations. Although these transporters contributed to pH_i recovery from acidosis, ATP had no effect. Nevertheless, ATP induced a small and reversible decrease in pH_i by 0.07 ± 0.02 pH-units and BzATP decreased pH_i by 0.29 ± 0.07 pH-units in –BIC (n=10, 11). These effects were abolished by Brilliant Blue and in Ca²⁺-free solutions. Our study shows that the pH_i effect of ATP is mediated by P2X₇ receptors. However, ATP does not affect H⁺/HCO₃^- transporters unmasked by cellular acidosis. Presumably, ATP alone does not stimulate HCO₃^- secretion in pancreatic ducts.

Inflammasome activation by danger signals: extracellular ATP and pH

“…1, right side) [11,20]. As for the ATP/P2X7R pathway, it has also been reported that ATP induced a reduction in intracellular pH in rat pancreatic ducts via P2X7R activation [22]. We further observed that the activation of the P2X7R by ATP induced an increase in lysosomal pH in microglial cells [23], which might have caused a reduction in cytosolic pH by impairing the intracellular proton balance.…”

P2X7 receptor expression is decreased in epithelial cancer cells of ectodermal, uro-genital sinus, and distal paramesonephric duct origin

“…The P2X 7 receptor is a membrane-bound, ligand-operated channel whose main function in epithelial cells is mediation of apoptosis [8][9][10]. The natural ligand of the P2X 7 receptor is adenosine triphosphate (ATP) [8,9], which is present in the extracellular fluid of epithelial cells at high nanomolar and low micromolar levels [11][12][13][14][15]. While ATP requirements of the P2X 7 receptor are higher than those of other purinergic receptors [8,9], the ATP levels in extracellular fluids suffice to activate the receptor [15].…”

Regulation of P2X7 gene transcription

“…The natural ligand of the receptor is ATP [15,16] which is present in the extracellular fluid of epithelial cells at concentrations that can activate the receptor [4,8,[18][19][20][21]. Binding of ATP to the P2X 7 receptor can activate various cell-specific signaling cascades, including the IL-1β [22], TNFα-TRAIL [23], and the p38, JNK / SAPK [24], and NF-κB cascades [25].…”