Regulation of intestinal calcium absorption by luminal calcium content: role of intestinal alkaline phosphatase

Mol Nutr Food Res. 2014 Jul;58(7):1546-51. doi: 10.1002/mnfr.201300686. Epub 2014 Apr 22.

Abstract

Scope: Intestinal alkaline phosphatase is a brush border enzyme that is stimulated by calcium. Inhibition of intestinal alkaline phosphatase increases intestinal calcium absorption. We hypothesized that intestinal alkaline phosphatase acts as a minute-to-minute regulatory mechanism of calcium entry. The aim of this study was to evaluate the mechanism by which intestinal luminal calcium controls intestinal calcium absorption.

Methods and results: We performed kinetic studies with purified intestinal alkaline phosphatase and everted duodenal sacs and showed that intestinal alkaline phosphatase modifies the luminal pH as a function of enzyme concentration and calcium luminal content. A decrease in pH occurred simultaneously with a decrease in calcium absorption. The inhibition of intestinal alkaline phosphatase by l-phenylalanine caused an increase in calcium absorption. This effect was also confirmed in calcium uptake experiments with isolated duodenal cells.

Conclusion: Changes in luminal pH arising from intestinal alkaline phosphatase activity induced by luminal calcium concentration modulate intestinal calcium absorption.

Keywords: Calcium; Calcium uptake; Intestinal alkaline phosphatase; Luminal calcium content.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaline Phosphatase / antagonists & inhibitors
  • Alkaline Phosphatase / metabolism*
  • Animals
  • Calcium / administration & dosage*
  • Calcium / pharmacokinetics
  • Duodenum / cytology
  • Duodenum / drug effects
  • Duodenum / metabolism
  • Female
  • Hydrogen-Ion Concentration
  • Intestinal Absorption*
  • Intestines / enzymology*
  • Microvilli / drug effects
  • Microvilli / metabolism
  • Phenylalanine / pharmacology
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Phenylalanine
  • Alkaline Phosphatase
  • Calcium