The immunohistolocalization of carbonic anhydrase in rodent tissues.

Carbonic anhydrase has been localized with an immunoenzyme bridge technique in the following sites in paraffin sections of fixed rodent tissues: gastric parietal cells, the brush border of enterocytes in the small intestine, superficial nongoblet cells of the colon, selective segments of the nephron, glial cells, erythrocytes and adipose cells. Immunocytochemical localizations of carbonic anhydrase isozymes I and II in different histologic sites, by means ofaffinity column purified antibodies, agreed with the distribution of these enzymes in the various sites, as indicated by immunologic assays. The immunocytoehemical results are compared with those reported for the cobalt-bicarbonate cytochemical method and with biochemical knowledge of the occurrence of carbonic anhydrase. Carbonic anhydrase varies in prevalence in different tissues, but the cell types containing abundant carbonic anhydrase in organs endowed with this enzyme remains largely undetermined. Cytochemicallocalization ofcarbonic anhydrase would provide information, not readily obtainable by biochemical techniques, about its relative distribution in different organs and activity in various cell types. Three isozymes of carbonic anhydrase, designated CA I, CA II, and CA III, are known to occur in mammals (24, 25, 38, 43). These isozymes are under the control of separate genetic loci, and the high degree of homology between their primary structures demonstrates their ancestry from a common gene (43, 46). Nevertheless, the rather marked differences in their activities, physicochemical properties and regulatory controls indicate that their physiological roles are different (5, 43, 44). It is also becoming apparent that the levels of these isozymes vary considerably from tissue to tissue. Clearly, knowledge of the cellular distribution and localization of carbonic anhydrase and its isoenzymes would contribute to a fuller understanding of the physiologic significance of these enzymes in the metabolism and function of various cell types. Four approaches have been employed to demonstrate carbonic anhydrase in cell types and in tissue sections: a radioautographic method employing a labelled-inhibitor (18, 19), cy