Carbonic anhydrase IV is expressed in H+-secreting cells of rabbit kidney

Carbonic anhydrase (CA) IV is a membrane-bound enzyme that catalyzes the de hydration of carbonic acid to CO2 and water. Using peptides from each end o f the deduced rabbit CA IV amino acid sequence, we generated a goat anti-ra bbit CA IV antibody, which was used for immunoblotting and immunohistochemi cal analysis. CA IV was expressed in a variety of organs including spleen, heart, lung, skeletal muscle, colon, and kidney. Rabbit kidney CA IV had tw o N-glycosylation sites and was sialated, the apparent molecular mass incre asing by at least 11 to similar to 45 kDa in the cortex. Medullary CA IV wa s much more heavily glycosylated than CA IV from cortex or any other organ, such modifications increasing the molecular mass by at least 20 kDa. CA IV was expressed on the apical and basolateral membranes of proximal tubules with expression levels on the order of S2 > S1 > S3 = 0. Because CA IV is b elieved to be anchored to the apical membrane by glycosylphosphatidylinosit ol, the presence of basolateral CA IV suggests an alternative mechanism. CA IV was localized on the apical membranes of outer medullary collecting duc t cells of the inner stripe and inner medullary collecting duct cells, as w ell as on alpha-intercalated cells. However, CA IV was not expressed by bet a-intercalated cells, glomeruli, distal tubule, or Henle's loop cells. Thus CA IV was expressed by H+-secreting cells of the rabbit kidney, suggesting an important role for CA IV in urinary acidification.