Regulation of intestinal calcium absorption by luminal calcium content. Role of intestinal alkaline phosphatase

BRUN LR; BRANCE ML; LOMBARTE M; LUPO M; DI LORETO V; RIGALLI A

MOLECULAR NUTRITION & FOOD RESEARCH

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2014

1613-4125

Intestinal alkaline phosphatase is a brush border enzyme that is stimulated by calcium. Inhibition of intestinal alkaline phosphatase increases intestinal calcium absorption. We hypothesised 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. 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. We concluded that the changes in luminal pH arising from intestinal alkaline phosphatase activity induced by luminal calcium concentration modulate intestinal calcium absorption.