The crypt-villus distribution of the 10,000 Mr intestinal calcium binding protein in human jejunum

The amount of small intestinal calcium-binding protein was studied in biopsies of human jejunum sectioned perpendicular to the long axis of the villi. Brush-border aminopeptidase N activity was measured to distinguish undifferentiated crypt cells from mature villus cells. The amount of calcium-binding protein as measured by enzyme-linked immunoadsorbent assay was highest at the villus tip and gradually decreased to near zero values in the crypt. The distribution of calcium-binding protein observed is parallel to that found in vitamin D repleted rats. The present study indicates that the mature enterocyte in man is fully committed to express calcium-binding protein in accordance with the view that these cells are considered the most active in the calcium absorptive mechanism.