Localization of carbonic anhydrase in the rat lung

The localization of carbonic anhydrase in the rat lung has been demonstrated, at light and electron microscopic levels, by the cobalt bicarbonate histochemical method of Hansson. Focal deposits of the cobalt sulfide reaction product were found not only in the capillary endothelium of the alveolar walls, but also in the small and large alveolar cells. The histochemical reaction was abolished by two potent inhibitors, acetazolamide (10(-5) to 10(-6) M) and KCNO (5 x 10(-3) to 10 x 10(-3) M). Physiological assay with Maren's method indicated that values for carbonic anhydrase activity in rat lung are 4.4 +/- 0.8 UA/mg of protein, 25.0 +/- 5.5 UA/mg of nitrogen, and 369 +/- 86 UA/g of wet weight. In addition, it was calculated that after fixation in glutaraldehyde-formaldehyde-picric acid about 9% activity is retained.