Carbonic anhydrase histochemistry in rabbit and mouse kidneys

The presence of carbonic anhydrase activity in rabbit and mouse kidneys was examined using a histochemical procedure with plastic embedded sections stained by the modified version of the cobalt-phosphate method (Hansson, 1967, 1968; Ridderstrale, 1976). Proximal convoluted tubules (S1 and S2 segments) in both species were strongly positive for carbonic anhydrase activity on the membranes of the luminal, lateral, and basal surfaces. The apical cytoplasm beneath the brush border and the nuclei also stained positively for carbonic anhydrase. The S3 segment (pars recta) of the proximal tubule in the rabbit was positive on the luminal membrane, with somewhat less intensity seen on the lateral and basal surfaces. This segment in the mouse was completely negative. The first part of the thin limbs of long-looped nephrons exhibited strong staining in the mouse. Faint luminal staining was present on descending thin limbs of short-looped nephrons in the mouse. In the rabbit, both the medullary and cortical ascending thick segments of the limb of Henle were completely negative. In contrast, the medullary and cortical ascending thick limbs in the mouse kidney showed staining on all plasma membranes. The intercalated cells in the cortical and medullary portion of the collecting tubules stained positively for carbonic anhydrase in both species. The principal cells of the collecting duct in the cortex were negative in the rabbit and faintly positive in the mouse. The principal cells in the upper medullary collecting tubules in both species stained intensely along the luminal, lateral, and basal cell membranes. The papillary collecting ducts were largely negative in both the rabbit and the mouse. Some interstitial cells in the rabbit in the region of the papillary tip were strongly positive. We conclude that there is a marked difference in carbonic anhydrase activity within and between the renal tubular segments of the rabbit and the mouse. In addition, these distinct differences that exist between the two species correlated with known physiological roles in ion transport.