Abstract
Isolated mouse duodenal epithelium, in the form of structurally intact crypt-villus units, was used to study the distribution of alkaline phosphatase with histochemistry. The tissue was incubated on ice in the medium of Hugon and Borgers (J Histochem Cytochem 14:629, 1966), with constant stirring to ensure uniform reaction. Continuous activity was observed frm the crypt mouth to the villus tip. A single band of alkaline phosphatase activity, 2-03 cell in height, was observed in the mid-crypt region in about 80% of crypts studied. Control studies (no substrate control, no lead control, pH control, inhibitor control, inactivated enzyme control, no enzyme control, and stimulator indeed due to alkaline phosphatase. The narrow band of activity in the crypt was also observed in vibratome sections of nonfrozen tissue. When isolated epithelium was subjected to a freeze-thaw cycle and then incubated in Hugon's medium, reaction product was observed continuously from the mid-crypt region to the villus tip. This pattern was similar to that observed with frozen sections. We conclude that alkaline phosphatase is present in an active form in epithelial cells in the region of the band. In epithelial cells above the band, e.e., in the upper crypt, alkaline phosphatase is present in an inactive form which may be activated by a freeze-thaw cycle.