Carbonic anhydrase I and II as a differentiation marker of human and rat colonic enterocytes.

Carbonic anhydrase (CA) is an enzyme that is expressed in the intestine and catalyzes the reversible hydration of CO2 in the following reaction: CO2 + H2O<==>H2CO3<==>H(+)+HCO3-. To elucidate the association of CA expression with the differentiation of colonic enterocytes, we investigated the expression and localization of CA using a Northern blotting analysis, Western blotting analysis, and immunohistochemical staining. A Northern blotting analysis revealed an abundant expression of CA I and II mRNA in the colonic epithelial cells. However, the expression of CA III mRNA was not detected. According to the results of immunohistochemical staining of the human colonic mucosa using antisera against CA I and II, both CA I and II were localized on the cytoplasm of non-goblet columnar cells in the upper half of the crypts where more differentiated cells are located. According to the results of immunohistochemical staining of the rat colonic mucosa, neither CA I and II were detected at the new-born stage. The expression of CAs in the upper half of the crypts began to rise from 1 week after birth, and thereafter increased according to the growth of the rats. At 3 weeks after birth, the expression of CAs was almost the same as that of the adult rats. The amount of CA proteins evaluated by a Western blotting analysis revealed that the expression of CAs increased gradually until reaching a maximum level at 6 or 8 weeks. These results therefore suggest that CA I and II appear to be good markers for the differentiation of enterocytes in the colonic mucosa.