title: Regulation of intestinal calcium absorption by luminal calcium content: role of intestinal alkaline phosphatase.
abstract: METHODS
  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.
  
  
  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.
  
  
  CONCLUSIONS
  Changes in luminal pH arising from intestinal alkaline phosphatase activity induced by luminal calcium concentration modulate intestinal calcium absorption.
authors.affiliation: Bone Biology Laboratory, School of Medicine, Rosario National University, Argentina.
authors.forename: Lucas R
authors.initials: LR
authors.lastname: Brun
authors.forename: María L
authors.initials: ML
authors.lastname: Brance
authors.forename: Mercedes
authors.initials: M
authors.lastname: Lombarte
authors.forename: Maela
authors.initials: M
authors.lastname: Lupo
authors.forename: Verónica E
authors.initials: VE
authors.lastname: Di Loreto
authors.forename: Alfredo
authors.initials: A
authors.lastname: Rigalli
mesh_terms: D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004386:Duodenum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007422:Intestines / Q000201:enzymology*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D010649:Phenylalanine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010649:Phenylalanine; D000469:Alkaline Phosphatase; D002118:Calcium
keywords: Calcium; Calcium uptake; Intestinal alkaline phosphatase; Luminal calcium content