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Physiological Consequences of Gill Remodeling in Goldfish ( Carassius Auratus) Resulting from Changes in Ambient Temperature Or Oxygen Levels

出版	Université d'Ottawa / University of Ottawa, 2009
URL	http://books.google.com.hk/books?id=oFeYXwAACAAJ&hl=&source=gbs_api

註釋Using two models of gill remodeling (thermally-induced and hypoxia-induced), experiments focused on the physiological consequences of changing SA (surface area) on Cl- balance in goldfish (Carassius auratus ). A central hypothesis was that increasing surface area (SA) associated with gill remodeling would pose a challenge to ionic regulation by promoting the obligatory trans-branchial movements of salt and water. To counter the presumed increased rates of Cl- loss, it was reasoned that goldfish experiencing greater SA would increased the numbers or activities of the putative Cl- transporting cells, the ionocytes. In fish acclimated to warm water (25° C), the ionocytes were scattered along the lamellae and within the interlamellar regions of the filament. In cold water (7° C), the ionocytes were absent from the lamellae and filaments but instead restricted to the outer regions of an interlamellar cell mass (ILCM) that formed within the interlamellar channels. It was determined that in fish transferred from 25 to 7° C, the ionocytes on the outer edge of the ILCM originated predominantly from the migration of pre existing ionocytes. The greater functional lamellar surface area in the warm water acclimated fish did not result in an increase of passive branchial Cl- efflux as was predicted on the basis of the increased paracellular movement of polyethylene glycol (PEG: 7.5 fold): these data suggest specific regulation (minimization) of Cl- loss. Despite a reduced surface area of ionocytes in the warm acclimated fish (2103 +/- 180 compared to 5219 +/-438 mum2 mm-1 of filament) and higher activities of Na+/K+-ATPase (NKA; 1.28 +/- 0.15 compared to 0.43 +/- 0.06 mumol mg-1 protein h -1), Cl- uptake was not significantly increased to match the elevated rate of Cl- efflux and thus the fish at 25° C were experiencing a net loss of Cl- across the gill which may have been countered by dietary gain of Cl-. Goldfish acclimated to 7° C and exposed to hypoxia (10 mm Hg) exhibited a pronounced remodeling of the gill consisting of the retraction of the ILCM which was accompanied by a significant decrease in the surface area of ionocytes owing to a decrease in their numbers as well as size. As observed for thermally-induced remodeling, it was demonstrated that during hypoxia, pre-existing ionocytes migrated with the shrinking ILCM while a smaller proportion of newly differentiated cells appeared below the surface of the ILCM. Despite the decrease in ionocyte surface area, an elevation of Na +/K+-ATPase activity was suggestive of increased branchial ion transport capacity yet rates of Cl- uptake were not any higher in the hypoxic fish. Similarly, despite an increase in functional lamellar surface area in the hypoxic fish, there was no corresponding increase in Cl - loss or efflux of PEG. However, when hypoxic fish were returned to normoxic water for 12 h, rates of Cl- and PEG efflux and Cl- uptake were markedly stimulated. These data demonstrate that despite experiencing an increase in functional lamellar surface area, hypoxic goldfish limit branchial Cl- loss likely by a hypoxia-mediated decrease in paracellular permeability that could be evident with the return of the fish to the normoxic water.