ABSTRACT. A full-length cDNA clone of an equine carbonic anhydrase (CA)-VI was obtained from the equine parotid gland. The cDNA sequence was 1338 bp long and was predicted to encode a 319 amino acid polypeptide with a putative signal peptide of 18 amino acids. The deduced amino acid sequence of mature CA-VI showed the similarity of 70% to those of other mammalians reported. Westernblot analysis using anti-horse CA-VI peptide detected the single band in parotid gland, and the band reduced its size by treatment with Nglycosidase F. Additionally, CA-VI protein expression was confirmed in submandicular gland and weakly in liver. In contrast, RT-PCR analysis revealed signals in the digestive tract including duodenum, jejunum, ileum, cecum and colon as well as the salivary glands. In addition, certain signals were detected in testis, thyroid gland and liver, but not in nerve tissue, skeletal muscle, spleen or lymph node.KEY WORDS: carbonic anhydrase, cDNA sequence, horse.

BackgroundCarbonic anhydrase VI (CA-VI) is produced by the salivary gland and is secreted into the saliva. Although CA-VI is found in the epithelial cells of distal straight tubule of swine kidneys, the exact function of CA-VI in the kidneys remains unclear.ResultsCA-VI was located in the epithelial cells of distal straight tubule of swine kidneys.A full-length cDNA clone of CA-VI was generated from the swine parotid gland by reverse transcription polymerase chain reaction, using degenerate primers designed based on conserved regions of the same locus in human and bovine tissues.The cDNA sequence was 1348 base pairs long and was predicted to encode a 317 amino acid polypeptide with a putative signal peptide of 17 amino acids. The deduced amino acid sequence of mature CA-VI was most similar (77.4%) to that of human CA-VI. CA-VI expression was confirmed in both normal and nephritic kidneys, as well as parotid. As the primers used in this study spanned two exons, the influence of genomic DNA was not detected. The expression of CA-VI was demonstrated in both normal and nephritic kidneys, and mRNA of CA-VI in the normal kidneys which was the normalised to an endogenous β–actin was 0.098 ± 0.047, while it was significantly lower in the diseased kidneys (0.012 ± 0.007). The level of CA-VI mRNA in normal kidneys was 19-fold lower than that of the parotid gland (1.887).ConclusionsThe localisation of CA-VI indicates that it may play a specialised role in the kidney.