Intestinal alkaline phosphatase is secreted bidirectionally from villous enterocytes

Am J Physiol. 1989 Jul;257(1 Pt 1):G14-23. doi: 10.1152/ajpgi.1989.257.1.G14.


A fraction of intestinal alkaline phosphatase (IAP) is secreted into blood. To study this process, enzyme secretion was examined in a fetal (IRD-98) and a differentiated (Caco-2) intestinal cell line. Tissue-unspecific alkaline phosphatase (AP) activity in the IRD-98 cells increased 20-fold after addition of 1.5 mM sodium butyrate and 40 mM NaCl, but no AP activity was secreted into the medium. In contrast, newly synthesized IAP in Caco-2 cells was secreted into the medium. AP secretion increased with time and was inhibited by monensin. Medium AP was still partially bound to membranes as assessed by Triton X-114 phase separation and could be released by the addition of serum. Analysis by sodium dodecyl sulfate polyacrylamide gels and by isoelectric focussing showed that secreted AP gave a pattern similar to that of the AP released from membranes by phospholipase D treatment. When Caco-2 cells were grown on filters, AP activity was found in both basolateral (75%) and luminal (25%) media. These data demonstrate that the secretion of a particulate AP with extracellular release from the membrane can account for the appearance of the intestinal isozyme in both the serum and the lumen.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenocarcinoma
  • Alkaline Phosphatase / metabolism*
  • Animals
  • Butyrates / pharmacology
  • Butyric Acid
  • Cell Differentiation
  • Cell Line
  • Colonic Neoplasms
  • Duodenum / drug effects
  • Duodenum / embryology
  • Duodenum / enzymology
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Ileum / drug effects
  • Ileum / enzymology
  • Intestines / drug effects
  • Intestines / enzymology*
  • Isoelectric Focusing
  • Microvilli / enzymology
  • Monensin / pharmacology
  • Phosphatidylinositol Diacylglycerol-Lyase
  • Phospholipase D / metabolism
  • Phospholipase D / pharmacology
  • Phosphoric Diester Hydrolases / metabolism
  • Rats
  • Sodium Chloride / pharmacology
  • Tumor Cells, Cultured


  • Butyrates
  • Butyric Acid
  • Sodium Chloride
  • Monensin
  • Alkaline Phosphatase
  • Phosphoric Diester Hydrolases
  • Phospholipase D
  • Phosphatidylinositol Diacylglycerol-Lyase