Carbonic anhydrase, ultrastructural localization in the mouse gastric mucosa and improvements in the technique.

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Abstract
The ultrastructural localization of carbonic anhydrase activity in mouse gastric mucosal cells as revealed by the cobalt bicarbonate histochemical method of Hansson has been made. In addition the effects of fixatives used for ultrastructural studies have been evaluated for reduction of carbonic anhydrase activity; exogenous erythrocyte carbonic anhydrase has been localized in tissues; acetazolamide and potassium cyanate inhibition of activity demonstrated; and an improved method for the osmication of reacted tissues for electron microscopy has been developed. The results indicate that the glutaraldehyde, formaldehyde, picric acid fixative, which retains about 5% of the original carbonic anhydrase activity, is distinctly better for histochemical studies than formaldehyde fixation, which retains about 32% activity. Acetazolamide at 10(-5) M consistently inhibits histochemical reaction, as does 20 mM KCNO, in the incubation medium. Exogenous carbonic anhydrase is readily visualized by the histochemical technique. Electron microscopy of gastric mucosa reacted for carbonic anhydrase activity indicates the focal deposition of the cobalt sulfide reaction product in the cores of microvilli lining the intracellular canaliculi, in the basal and lateral cell folds of parietal cells, and in the microvilli as well as the cytoplasm between mucous granules in the surface mucous cells. In addition, some reaction product was found in the mitochondrial cristae and in some nuclei and intercellular spaces.