TY - JOUR
T1 - Defecation and the fate of dietary sodium in the common killifish (Fundulus heteroclitus macrolepidotus Walbaum, 1792)
AU - Wood, Chris M.
AU - Bucking, Carol
N1 - Funding Information:
We thank Linda Diao and Sunita Nadella for excellent technical assistance. This work was supported by an NSERC (Canada) Discovery Grant to CMW, who is also supported by the Canada Research Chair Program . CB was supported by an NSERC Canada Postgraduate Scholarship . The funding agencies had no role in the design of the study. [SS]
Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.
PY - 2012/12/1
Y1 - 2012/12/1
N2 - While uptake of Na + from the water is well-characterized in fish, little is known about the uptake of Na + from the diet. A method involving radiolabeling of the diet with [ 22Na +] and [ 3H] PEG-4000 has been developed to study this process, and to separate the systemic efflux of absorbed [ 22Na +] via gills and kidney from the potential efflux of [ 22Na +] into the water via defecation. Killifish were acclimated to 10% sea water, a typical salinity for this estuarine fish where they are hyperosmotic to the environment. The fish were fed a single meal (0.81% ration, containing 5.09μmol total Na +gbody weight -1) of re-pelleted food labeled with both radiotracers. Effluxes into the water were monitored for 48h. Sharp increases in [ 3H] PEG-4000 appearance provided a clear definition of defecation events, which started at about 7h post-feeding and finished by 16h, with the midpoint at 11.5h. In contrast, the evolution of [ 22Na +]-radioactivity in the water showed a smooth curvilinear relationship starting at 3h, with a gradually declining slope through 48h. There was no efflux of [ 22Na +] associated with defecation events, showing that all [ 22Na +] was quickly absorbed from the meal. By 48h, about 50% of the consumed [ 22Na +] had been excreted to the external water by systemic efflux. The efflux relationship was best described by a two-phase exponential relationship, with a breakpoint at about 13h post-feeding. The first phase (rate constant 0.0309h -1) corresponded to branchial efflux of dietary [ 22Na +] equilibrated with the exchangeable whole body Na + pool, while the second phase was much slower (0.0114h -1). These results emphasize the importance of dietary Na + when the killifish is hyper-regulating, and provide a method applicable to a wide range of conditions, ions, and species.
AB - While uptake of Na + from the water is well-characterized in fish, little is known about the uptake of Na + from the diet. A method involving radiolabeling of the diet with [ 22Na +] and [ 3H] PEG-4000 has been developed to study this process, and to separate the systemic efflux of absorbed [ 22Na +] via gills and kidney from the potential efflux of [ 22Na +] into the water via defecation. Killifish were acclimated to 10% sea water, a typical salinity for this estuarine fish where they are hyperosmotic to the environment. The fish were fed a single meal (0.81% ration, containing 5.09μmol total Na +gbody weight -1) of re-pelleted food labeled with both radiotracers. Effluxes into the water were monitored for 48h. Sharp increases in [ 3H] PEG-4000 appearance provided a clear definition of defecation events, which started at about 7h post-feeding and finished by 16h, with the midpoint at 11.5h. In contrast, the evolution of [ 22Na +]-radioactivity in the water showed a smooth curvilinear relationship starting at 3h, with a gradually declining slope through 48h. There was no efflux of [ 22Na +] associated with defecation events, showing that all [ 22Na +] was quickly absorbed from the meal. By 48h, about 50% of the consumed [ 22Na +] had been excreted to the external water by systemic efflux. The efflux relationship was best described by a two-phase exponential relationship, with a breakpoint at about 13h post-feeding. The first phase (rate constant 0.0309h -1) corresponded to branchial efflux of dietary [ 22Na +] equilibrated with the exchangeable whole body Na + pool, while the second phase was much slower (0.0114h -1). These results emphasize the importance of dietary Na + when the killifish is hyper-regulating, and provide a method applicable to a wide range of conditions, ions, and species.
KW - [ Na ]
KW - [ H] PEG-4000
KW - Feeding
KW - Gills
KW - Intestine
KW - Ionoregulation
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U2 - 10.1016/j.jembe.2012.08.002
DO - 10.1016/j.jembe.2012.08.002
M3 - Article
AN - SCOPUS:84865574219
VL - 434-435
SP - 53
EP - 57
JO - Journal of Experimental Marine Biology and Ecology
JF - Journal of Experimental Marine Biology and Ecology
SN - 0022-0981
ER -