Immunolocalization of Na+, K+-ATPase and lonocytes in the gills of catfish, silurus glanis

The regulation of the body fluid content [osmoregulation] of an aquatic animal, is performed by several organs. In fish, osmoregulatory mechanisms are based on the function of specialized cells [ionocytes] located in various tissues and organs including gills. Na[+],K [+]- ATPase is one of the [most] osmoregulatory enzymes enabling the use of ATP as a source of energy for ion transport through a Na[+],K[+] exchange pump cross epithelial membranes of ionocytes. The aim of this study was localization of this enzyme and ionocytes in the gills of S. glanis. For light microscopic observation, samples were fixed in Buin for 24 h dehydrated with ethanol, and embedded in paraffin. Serial section, 5 micro m thick, was stained by the Haematoxylin, Eosin and Methyl green. Immunolocalization of the Na[+],K[+] -ATPase was performed by immunofluorescence light microscopy with a Mouse Monoclonal Antibody IgG alpha 5 raised against the alpha-subunit of the Chicken Na+,K +/- ATPase [Developmental Studies Hybridoma Bank, University of Iowa, USA] and a Mouse Anti-fluorescein Antibody FITC [Jackson Immuno Research, USA]. In longitudinal sections of the gill, two series of lamellae were observed on both sides of the filaments. Gill filaments and lamellae were lined by special cells, contained pavement cells, mucous cells and ionocytes. The ionocytes were located in the basal parts of lamellae, inter-lamellar regions and in the apical parts of gill filaments. The ionocytes showed a ovoid-spheroid shape with a strong immunofluorescence of Na[+],K[+] -ATPase in the baso-lateral regions. In catfish, S. glanis, the ionocytes was found to be distributed on filaments and mainly in inter-lamellar regions. Na[+],K[+] -ATPase enzyme with a highly consistent immunoreactivity was observed in the baso-lateral parts of the ionocytes. These findings show that, in S. glanis, the filaments appear as the main site of osmoregulation and the gill lamellae are mainly devoted to respiration

Gill diffusion as a physiological mechanism for hydrogen peroxide elimination by fish

Hydrogen peroxide is metabolized by the specific enzymatic action of catalase and glutathione peroxidase in animal tissues. The relatively low catalase and glutathione peroxidase activities found in the blood of fish may be related to the ability of gills to eliminate hydrogen peroxide into the aquatic environment. Poecilia vellifera releases hydrogen peroxide apparently by gill diffusion into the environment, resulting in a steady-state H2O2 concentration of about 0.6 µM in the surrounding water. This physiological mechanism resembles ammonia excretion by teleost fish