title: Biochemical properties and immunohistochemical localization of carbonic anhydrase in the sacculus of the inner ear in the salmon Oncorhynchus masou.
abstract: Carbonic anhydrase (CA) in the inner ear sacculus was examined by activity assay, Western blotting and immunohistochemistry to determine its role in otolith calcification. An immunoreactive protein with a molecular mass of approximately 28 kDa was detected by Western blotting. The CO2 hydration activity in the cytosol fraction of the sacculus was 5.4 units/mg protein, while little or no activity was detected in the nuclear and mitochondrial fractions. The enzyme activity was highly inhibited by acetazolamide. The concentration of 50% inhibition was 8.16 nM and the inhibition constant of the activity was 8.25 nM. Transitional and squamous epithelial cells of the sacculus were immunopositive with an anti-CA II antibody, but sensory epithelial cells and mitochondria-rich cells in the transitional epithelium were not. These results suggest that transitional epithelial cells other than mitochondria-rich cells and squamous epithelial cells play an important role in otolith calcification by supplying bicarbonate to otoliths and/or by eliminating protons from endolymph.
authors.affiliation: Laboratory of Comparative Physiology, Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate 041-8611, Japan. atohse@mail.ecc.u-tokyo.ac.jp
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Tohse
authors.forename: Hitomi
authors.initials: H
authors.lastname: Ando
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Mugiya
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002256:Carbonic Anhydrases / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D007150:Immunohistochemistry; D008928:Mitochondria / Q000201:enzymology; D012444:Saccule and Utricle / Q000201:enzymology*; D012474:Salmon
chemical_list: D002256:Carbonic Anhydrases