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First published online February 27, 2009
Journal of Experimental Biology 212, 843-852 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.025999

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The effects of thermally induced gill remodeling on ionocyte distribution and branchial chloride fluxes in goldfish (Carassius auratus)

D. Mitrovic and S. F. Perry^*

Department of Biology, 30 Marie Curie, Ottawa, ON, Canada, K1N 6N5

View larger version (49K): [in this window] [in a new window]   Fig. 1. The effects of acclimation temperature on relative interlamellar cell mass (ILCM) surface area in gills of goldfish (Carassius auratus) (A) The surface area of the ILCM (expressed as a percentage of total interlamellar area) was decreased (indicated by asterisk) in fish acclimated to 25°C (N=6) when compared with fish kept at 7°C (N=6); data are presented as means ± 1 s.e.m. (B,C) Representative light micrographs illustrate the marked differences in the extent of the ILCM (single ILCMs outlined in black) in the two groups of fish as well as the obvious increase in functional lamellar surface area in fish acclimated to 25°C; scale bars, 20 µm. The ionocytes are stained black.

View larger version (56K): [in this window] [in a new window]   Fig. 2. The effects of acclimation temperature on the surface area of ionocytes (as determined using osmium-zinc iodide staining) and their distribution in goldfish (Carassius auratus). (A) The surface area of ionocytes (arrows) was significantly decreased (indicated by asterisk) in fish acclimated to 25°C (N=6) when compared with fish kept at 7°C (N=6); data are presented as means ± 1 s.e.m. (B,C) Representative light micrographs illustrate that the decrease in ionocyte surface area in fish acclimated to 25°C was a result of decreased numbers and sizes of individual cells (see Table 1). Note that the ionocytes were confined to the outer edge of the ILCM in the fish acclimated to 7°C; scale bars, 20 µm.

View larger version (47K): [in this window] [in a new window]   Fig. 3. The effects of acclimation temperature on the surface area of ionocytes (as determined by Na+/K+-ATPase immunofluorescence) and their distribution in goldfish (Carassius auratus). (A) The surface area of ionocytes was significantly decreased (indicated by asterisk) in fish acclimated to 25°C (N=6) when compared with fish kept at 7°C (N=6); data are presented as means ± 1 s.e.m. (B,C). Representative light micrographs illustrate that the decrease in ionocyte (arrows) surface area in fish acclimated to 25°C was a result of decreased numbers and sizes of individual cells (see Table 1). Note that the ionocytes were confined to the outer edge of the ILCM in the fish acclimated to 7°C; scale bars, 20 µm. Sections were labeled with DAPI-containing mounting media to show cell nuclei (blue).

View larger version (7K): [in this window] [in a new window]   Fig. 4. The effects of acclimation temperature on the (A) branchial Na+/K+-ATPase (NKA) activity and (B) relative NKA mRNA levels in goldfish (Carassius auratus). (A) Branchial NKA activity was increased (indicated by asterisk) in fish acclimated to 25°C (N=6) when compared with fish acclimated to 7°C (N=6). (B) The expression of NKA mRNA in the fish acclimated to 25°C (N=6) was not significantly increased (P=0.065) when compared to fish at 7°C (N=6) assigned a relative value of 1. Data are presented as means ± 1 s.e.m.

View larger version (66K): [in this window] [in a new window]   Fig. 5. The effects of decreasing temperature on the redistribution of branchial ionocytes. Live fish were bathed in TMMitotracker red and over the period of 2 weeks the temperature was brought down from 25°C to 7°C (N=6); the gills were fixed, sectioned and incubated with 5 antibody (green) to label Na+/K+-ATPase-positive ionocytes. Thus, after 2 weeks, pre-existing ionocytes would either be single labeled red or doubled labeled red and green, while newly formed ionocytes would be single labeled and appear green only. (A) The lowering of ambient temperature from 25°C to 7°C resulted in a significant increase (indicated by asterisk) in the number of newly formed ionocytes (unfilled portions of bars) while the number of pre-existing ionocytes was also increased (filled portions of bars) when compared to fish maintained at 7°C. Data are presented as means ± 1 s.e.m. (B,C) After 2 weeks, proliferation of the interlamellar cell mass appeared to be accompanied by the migration of pre-existing ionocytes. Scale bar, 20 µm. (D,E) Newly formed ionocytes (arrows) were appearing in the ILCM. Scale bar: 20 µm; All cells were labeled with DAPI mounting medium to show cell nuclei (blue).

View larger version (7K): [in this window] [in a new window]   Fig. 6. The effects of acclimation temperature on (A) branchial Cl– efflux (JOUTCl–; N=6 for each temperature) and (B) whole body Cl– influx (JINCl–; N=6 for each temperature) in goldfish, Carassius auratus. There were no statistically significant differences between the two groups of fish; data are shown as means ± 1 s.e.m.

View larger version (4K): [in this window] [in a new window]   Fig. 7. The effects of acclimation temperature on branchial efflux of polyethylene glycol (PEG) in goldfish, (Carassius auratus). Data are presented as means ± 1 s.e.m.; significant difference from 7°C is indicated by an asterisk.

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