Postnatal development of carbonic anhydrase IV expression in rabbit kidney

Carbonic anhydrase (CA) IV activity facilitates renal acidification by cata lyzing the dehydration of luminal carbonic acid. CA IV has been localized t o the proximal tubules and medullary collecting ducts. Maturation of CA TV expression has been considered to be important in the development of renal acid excretion. The purpose of the present study was to determine the matur ational expression of CA TV in rabbit kidney. A guinea pig polyclonal antib ody to purified rabbit lung microsomal membrane CA IV was generated. Immuno blotting of membrane proteins after peptide-N-glycosidase F treatment revea led two N-glycosylation sites and reduction in size from similar to 52 to 3 5 kDa; there appeared to be heavier glycosylation in the medulla. In membra ne and total proteins from the kidney cortex, CA TV was 15-30% of the adult ; level during the first 2 wk of life but increased to mature levels by 5 w k of age. The maturational pattern in the cortex was confirmed by measuring SDS-resistant CA hydratase activity. In the medulla, both membrane and tot al proteins were generally less than one-fourth of the adult level of CA TV during the first 2 wk of life before reaching mature levels by 5 wk of age . Immunohistochemistry showed staining in proximal tubules (apical > basola teral), with maximal label in the S2 segment. CA IV also appeared on the ap ical membranes of a minority cell type of the cortical collecting duct, pre sumably the cr-intercalated cell. Several labeled cells also appeared to be the process of being extruded from medullary collecting ducts of 1- to 2-w k rabbits. The antibody did not reliably detect medullary CA IV expression in sections from mature rabbits. These studies indicate that there is a sub stantial postnatal increase in expression of CA TV in the maturing kidney i n both the cortex and medulla. The disappearance of intercalated cells in t he maturing rabbit medullary collecting duct may be part of a normal renal developmental program as previously reported [J. Kim, J.-H. Cha, C. C. Tish er, and K. M. Madsen. Am. J. Physiol. 270 (Renal Fluid Electrolyte Physiol. 39). F575-F592, 1996]. It is likely that the maturation of CA IV expressio n contributes to the increase in renal acidification observed early in post natal life.