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

Abstract

Carbonic anhydrase (CA) IV is a membrane-bound enzyme that catalyzes the dehydration of carbonic acid to CO(2) and water. Using peptides from each end of the deduced rabbit CA IV amino acid sequence, we generated a goat anti-rabbit CA IV antibody, which was used for immunoblotting and immunohistochemical analysis. CA IV was expressed in a variety of organs including spleen, heart, lung, skeletal muscle, colon, and kidney. Rabbit kidney CA IV had two N-glycosylation sites and was sialated, the apparent molecular mass increasing by at least 11 to approximately 45 kDa in the cortex. Medullary CA IV was 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 believed to be anchored to the apical membrane by glycosylphosphatidylinositol, the presence of basolateral CA IV suggests an alternative mechanism. CA IV was localized on the apical membranes of outer medullary collecting duct cells of the inner stripe and inner medullary collecting duct cells, as well as on alpha-intercalated cells. However, CA IV was not expressed by beta-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.

Roles of cytosolic and membrane-bound carbonic anhydrase in renal control of acid-base balance in rainbow trout,Oncorhynchus mykiss

“…Although it has been shown that the proximal tubule of trout, like that of mammals, is composed of discrete sections (e.g., P1 and P2 in fish) (1), we were unable to reliably distinguish P1 from P2 segments based on standard morphological criteria (thickness of the brush border and position of nuclei). In mammals, CA IV is expressed on the apical and basolateral membranes of S2 and S1 proximal tubules (36,46). The presence of tCA IV within the brush border of proximal tubules is consistent with the role of this segment of the nephron in reabsorbing the majority of HCO 3 Ϫ from the renal filtrate.…”

“…In mammals, ϳ80 -90% of renal HCO 3 Ϫ reabsorption occurs within the proximal tubules. According to current models (42,48), filtered HCO 3 Ϫ combines with H ϩ , derived from an apical membrane sodium proton exchanger isoform 3 (NHE3) (65), to form CO 2 , a reaction that is catalyzed by membrane-bound carbonic anhydrase isoform IV (CA IV) (35,46). The newly formed CO 2 enters the proximal tubule cell where it is hydrated to H ϩ and HCO 3 Ϫ in the presence of CA isoform II (CA II) (59).…”

Localization of Carbonic Anhydrase XII to the Basolateral Membrane of H+-secreting Cells of Mouse and Rat Kidney

“…IHC studies have revealed CA IV in basolateral membranes of proximal tubules of rat and rabbit kidney (Brown et al 1990;Schwartz et al 2000). In our recent IHC study, CA XIV protein was also present in basolateral membranes of the proximal tubules and in the initial portion of the thin descending limb of Henle (Kaunisto et al 2002).…”

LC-MS/MS Analysis of Apical and Basolateral Plasma Membranes of Rat Renal Collecting Duct Cells

“…It is interesting to note that six other GPIlinked proteins were identified in the non-fixed perfusion-biotinylated IMCDs. Of them, CD59 (38) and carbonic anhydrase IV (39) have been shown to be expressed in apical membrane of human and rabbit IMCDs.…”