Dysfunction of the proximal tubule (PT) is associated with variable degrees of solute wasting and low-molecular-weight proteinuria. We measured metabolic consequences and adaptation mechanisms in a model of inherited PT disorders using PT cells of ClC-5-deficient (Clcn5Y/-) mice, a well-established model of Dent's disease. Compared to cells taken from control mice, those from the mutant mice had increased expression of markers of proliferation (Ki67, proliferative cell nuclear antigen (PCNA), and cyclin E) and oxidative scavengers (superoxide dismutase I and thioredoxin). Transcriptome and protein analyses showed fourfold induction of type III carbonic anhydrase in a kidney-specific manner in the knockout mice located in scattered PT cells. Kidney-specific carbonic anhydrase type III (CAIII) upregulation was confirmed in other mice lacking the multiligand receptor megalin and in a patient with Dent's disease due to an inactivating CLCN5 mutation. The type III enzyme was specifically detected in the urine of mice lacking ClC-5 or megalin, patients with Dent's disease, and in PT cell lines exposed to oxidative stress. Our study shows that lack of PT ClC-5 in mice and men is associated with CAIII induction, increased cell proliferation, and oxidative stress.

The distribution of bovine carbonic anhydrase isozyme VI (CA-VI), purified from bovine saliva, was studied immunohistochemically using antiserum against bovine CA-VI in bovine parotid glands during fetal and postnatal development. A weak expression of CA-VI in undifferentiated epithelial cells and ductal cells was observed in a 4- to 5-month-old fetus with a 26-cm crown-rump length. The reaction in both acinar and ductal cells subsequently persisted during late gestation and birth. Although anti-CA-VI reactivity was still seen in both regions immediately following birth, the reactivity had almost completely disappeared from most duct segments by 1 month following birth. Changes in the localization and time-dependent expression of the isozyme in parotid glands may reflect changes in the biological function of structurally closely related isozymes.

ABSTRACT. In the present study, we firstly demonstrated immunohistochemical expressions of secretory carbonic anhydrase (CA-VI) isozyme in bovine forestomach, large intestine and major salivary glands. CA-VI was detected in basal layer epithelial cells of esophageal and forestomach stratified epithelium, in mucous cells of upper glandular region of large intestine, in serous acinar cells of the parotid gland, in serous demilune cells and some ductal liner cells of mandibular, monostomatic sublingual and esophageal glands. These immunohistolocalizations suggested that bovine CA-VI plays various roles in pH regulation, maintenance of ion and fluid balance, and cell proliferation. KEY WORDS: bovine digestive organs, CA-VI, immunohistochemical localization.J. Vet. Med. Sci. 68(2): 131-135, 2006 Carbonic anhydrase isozyme-VI (CA-VI) is a unique secretory type CA isozyme. It was initially discovered and purified from ovine saliva [7], and then rat saliva [6,21], human saliva [13,20,22,25] and bovine saliva [5]. Fernley et al. [8] examined sheep CA-VI in 18 different tissues from sheep using biochemical analysis. They observed an immunoreactive signal for CA-VI only in parotid and mandibular glands, which suggested that CA-VI increased buffering capacity in the oral cavity. Some studies have identified the acinar cells of salivary glands as the origin of CA-VI in several species [5,8,21,22,25]. These studies have shown that CA-VI was present in acinar cells of the mammalian parotid and mandibular glands, from where CA-VI is secreted into the saliva. However, CA-VI expression in other segments of the alimentary canal has received little information and the precise physiological role of bovine CA-VI has never been revealed. The present study examines the immunohistochemical expression of CA-VI in bovine alimentary canal and in major salivary glands, and conjectures the function of CA-VI in the bovine digestive organs. MATERIALS AND METHODSTissue: Three adult Holstein cows were used in the present study. Small tissue blocks were prepared for microscopic observation. Samples were cut from the parotid, mandibular, and monostomatic sublingual glands, from cervical to thoracic segments of the esophagus, rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum, colon and rectum. The samples were immediately fixed in Bouin's solution, and then sliced into 3 µm-thick sections. CA-VI antibody:We purified CA-VI from bovine saliva as described previously [5]. A rabbit polyclonal antibody has been raised against purified bovine CA-VI and specific immunity to bovine CA-VI has been confirmed [5]. Briefly, the antibody against purified bovine CA-VI was produced in the rabbit. Rabbits were injected initially with 1 mg of purified CA-VI emulsified with an equal volume of Freund's complete adjuvant, followed by a weekly booster injection of a fixed amount of the enzyme for 5 weeks. The rabbits were bled via the auricular vein 10 days following the last injection. The specificity of the antiserum was confirmed by the doubl...

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The CA-III ELISA we developed was a sensitive method for determining CA-III concentrations in plasma, serum samples, and tissue specimens of dogs. Use of this ELISA requires only a small volume of serum and may enable the study of changes in CA isoenzyme concentrations associated with muscle disorders in dogs.