TY - JOUR
T1 - Intestinal alkaline phosphatase is secreted bidirectionally from villous enterocytes
AU - Sussman, N. L.
AU - Eliakim, R.
AU - Rubin, D.
AU - Perlmutter, D. H.
AU - DeSchryver-Kecskemeti, K.
AU - Alpers, D. H.
PY - 1989
Y1 - 1989
N2 - 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.
AB - 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.
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AN - SCOPUS:0024373334
SN - 0193-1857
VL - 257
SP - 20/1
JO - American Journal of Physiology - Gastrointestinal and Liver Physiology
JF - American Journal of Physiology - Gastrointestinal and Liver Physiology
IS - 1
ER -