کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4395929 | 1618439 | 2012 | 5 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Defecation and the fate of dietary sodium in the common killifish (Fundulus heteroclitus macrolepidotus Walbaum, 1792) Defecation and the fate of dietary sodium in the common killifish (Fundulus heteroclitus macrolepidotus Walbaum, 1792)](/preview/png/4395929.png)
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 5.09 μmol total Na+ g body weight− 1) of re-pelleted food labeled with both radiotracers. Effluxes into the water were monitored for 48 h. Sharp increases in [3H] PEG-4000 appearance provided a clear definition of defecation events, which started at about 7 h post-feeding and finished by 16 h, with the midpoint at 11.5 h. In contrast, the evolution of [22Na+]-radioactivity in the water showed a smooth curvilinear relationship starting at 3 h, with a gradually declining slope through 48 h. There was no efflux of [22Na+] associated with defecation events, showing that all [22Na+] was quickly absorbed from the meal. By 48 h, 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 13 h post-feeding. The first phase (rate constant 0.0309 h− 1) corresponded to branchial efflux of dietary [22Na+] equilibrated with the exchangeable whole body Na+ pool, while the second phase was much slower (0.0114 h− 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.
► A radiotracer method has been developed for studying dietary Na+ uptake in fish.
► [3H] PEG-4000 efflux provides a clear signal of defecation events.
► 22Na+ was rapidly absorbed from the intestine in killifish.
► 50% of absorbed 22Na+ was excreted by systemic efflux by 48 h.
► 22Na+ was not effluxed in defecation.
Journal: Journal of Experimental Marine Biology and Ecology - Volumes 434–435, 1 December 2012, Pages 53–57