Brush border intestinal alkaline phosphatase inversely regulates luminal ATP signaling in rat duodenum

Abstract

Duodenal bicarbonate secretion (DBS) creates a juxtamucosal alkaline microclimate, enhancing brush border intestinal alkaline phosphatase (IAP) activity. We hypothesized that IAP degrades luminal purines such as ATP, regulating DBS via P2Y receptors. We measured DBS with a pH‐stat or with pH and CO2 electrodes. We tested the effect of the perfusion of the IAP inhibitor L‐cysteine or glycerol phosphate, the ecto‐ATPase apyrase, the P2 receptor antagonist suramin or several P2 receptor agonists (2MeSATP, INS45973, UTP, UDP, ATPγS) on basal or acid‐induced DBS. Furthermore, we measured perfusate ATP content with luciferin‐luciferase. AP inhibition increased DBS, inhibited by suramin, with increased luminal ATP content. Acid augmented DBS, which was enhanced by L‐cysteine (with ATP increase) but reduced by apyrase (with ATP decrease). Increased luminal ATP content was not due to cellular injury. Immunohistochemistry localized P2Y1 receptors to the brush border membrane of duodenal villi. The P2Y1 agonist 2MeSATP, but not other agonists increased DBS. IAP inhibition increased DBS and luminal ATP content, consistent with ATP degradation by IAP. Luminal ATP stimulates DBS via P2Y1, consistent with an ecto‐purinergic regulatory system. Increased DBS augments IAP activity, which degrades ATP and decreases ATP‐mediated DBS, forming a negative feedback loop.