Biochemical properties and immunohistochemical localization of carbonic anhydrase in the sacculus of the inner ear in the salmon Oncorhynchus masou |
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Authors: | Tohse Hidekazu Ando Hitomi Mugiya Yasuo |
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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 |
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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. |
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