Long-term acclimation of the teleost Oreochromis mossambicus to various salinities: two different strategies in mastering hypertonic stress |
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Authors: | D. Kültz H. Onken |
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Affiliation: | (1) WB Tierphysiologie, Universität Rostock, FB Biologie, Universitätsplatz 2, D-18055 Rostock, Germany;(2) Institut für Tierphysiologie, Freie Universität Berlin, Grunewaldstraße 34, D-12165 Berlin, Germany;(3) Department of Zoology, Oregon State University, Cordley Hall 3029, 97331-2914 Corvallis, Oregon, USA |
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Abstract: | Laboratory-reared tilapia (Oreochromis mossambicus) were long-term acclimated to freshwater (FW), brackish water (BW, 10 salinity), seawater (SW, 35 salinity) and two hypersaline media (45 and 60 salinity). We examined the influence of these ambient salinities on the density (Dcc) and diameter (dcc) of DASPMI-stained chloride cells and on the capacity for electrogenic Cl- secretion of the in vitro opercular epithelium. To provide a characterisation of Cl- secretion, transepithelial potential difference (PDte), conductance (Gte) and short-circuit current (Isc) were measured after mounting the respective epithelium in an Ussing-chamber. The cellular electromotive forces (Ec) and conductances (Gc) as well as the leak conductances (Gl) were obtained from Gte: Isc plots. In the salinity range between FW and SW both Dcc and dcc increased. All electrophysiological parameters recorded increased in parallel, indicating a strong enhancement of the capacity for Cl- secretion on the cellular and epithelial level. In the salinity range above SW a further increase of Dcc was observed. However, despite a higher concentration gradient across the body surface of the tilapia during acclimation to hypersaline media, the short-circuit current (Isc) was not significantly different compared to SW preparations. This reflects proportional decreases of Gc and increases of Ec, respectively. Of particular interest, we found a strong decrease of the leak conductance (Gl) in preparations from tilapia acclimated to hypersaline media compared to those from SW fish, indicating that the tight junctions become less permeable. |
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