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Rectal water absorption in seawater-adapted Japanese eel Anguilla japonica

Rectal water absorption in seawater-adapted Japanese eel Anguilla japonica,10.1016/j.cbpa.2008.07.016,Comparative Biochemistry and Physiology A-molecu

Rectal water absorption in seawater-adapted Japanese eel Anguilla japonica   (Citations: 6)
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Marine teleosts drink large amounts of seawater to compensate for continuous osmotic water loss. We investigated a possible significant role of the rectum in water absorption in seawater-adapted eel. In rectal sacs filled with balanced salt solution (BSS) and incubated in isotonic BSS, water absorption was greater in seawater-adapted eel than in freshwater eel. Since rectal fluid osmolality was slightly lower than plasma osmolality in seawater-adapted eel, effects of rectal fluid osmolality on water absorption were examined in rectal sacs filled with artificial rectal fluid with different osmolality. Rectal water absorption was greater at lower rectal fluid osmolality, suggesting that an osmotic gradient between the blood and rectal fluid drives the water movement. Ouabain, a specific inhibitor of Na+/K+-ATPase, inhibited water absorption in rectal sacs, indicating that an osmotic gradient favorable to rectal water absorption was created by ion uptake driven by Na+/K+-ATPase. Expression levels of aquaporin 1 (AQP1), a water-selective channel, were significantly higher in the rectum than in the anterior and posterior intestines. Immunoreaction for Na+/K+-ATPase was detected in the mucosal epithelial cells in the rectum with more intense staining in the basal half than in the apical half, whereas AQP1 was located in the apical membrane of Na+/K+-ATPase-immunoreactive epithelial cells. The rectum is spatially separated from the posterior intestine by a valve structure and from the anus by a sphincter. Such structures allow the rectum to swell as intestinal fluid flows into it, and a concomitant increase in hydrostatic pressure may provide an additional force for rectal water absorption. Our findings indicate that the rectum contributes greatly to high efficiency of intestinal water absorption by simultaneous absorption of ions and water.
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    • ...(the posterior intestine and rectum), where the decreased osmolality of ingested SW is favorable to osmotic water movement across the intestinal epithelium from the mucosal to serosal side [7, 8]...
    • ...It has been reported that AQP1 is preferentially localized in the apical membrane of epithelial cells in posterior and rectal regions of the intestinal tract in SW-transferred Japanese eel [7, 8]. The gene expression of AQP1 in the intestine was higher in SW eel than in FW eel...
    • ...For the following experiments, the eel intestine was divided into three parts according to its external appearance: the anterior intestine, the posterior intestine (also referred to as the middle intestine) and the rectum [8]...
    • ...in Japanese and European eels and European sea bass [7, 8, 28, 39]...
    • ...Our previous study revealed that AQP1 is located preferentially in the apical membrane of intestinal epithelial cells, with more intense staining seen in the posterior intestine and rectum of the SW Japanese eel [7, 8]. It has also been shown that AQP1 abundance is correlated with water absorption in the intestine and rectum [7, 8]. These findings imply that AQP1 may act as a water entry site in intestinal epithelial cells...
    • ...Our previous study revealed that AQP1 is located preferentially in the apical membrane of intestinal epithelial cells, with more intense staining seen in the posterior intestine and rectum of the SW Japanese eel [7, 8]. It has also been shown that AQP1 abundance is correlated with water absorption in the intestine and rectum [7, 8]. These findings imply that AQP1 may act as a water entry site in intestinal epithelial cells...
    • ...In SW-acclimated Japanese eel, we have previously reported that the highest level of water absorption rate was observed in the rectum, followed in descending order by the posterior and anterior intestines [7, 8]. Considering the higher expression levels of AQPs 1, 3 and 8 in the rectum of the SW eel than in that of the FW eel, it is most likely that those AQPs are mainly involved in rectal water absorption in the SW eel; water in the ...

    Yi Kyung Kimet al. Expression of aquaporins 3, 8 and 10 in the intestines of freshwater- ...

    • ...including the rectum, osmolality of ingested seawater is reduced to isotonic or hypotonic levels [6], followed by passive absorption of water through aquaporin, a water channel, located at the apical membrane of intestinal epithelial cells [6–9]...
    • ...It is essential for water absorption in the intestine to reduce osmolality of ingested seawater to isotonic or subisotonic levels, since the major driving force for intestinal water absorption is an osmotic gradient created between the intestinal and body fluids [6, 8]. In the present study, we clearly showed that Ca precipitate formation in seawater-acclimated eel contributed greatly to the removal of Ca 2? , and of Mg 2? to a lesser ...

    Miyuki Mekuchiet al. Mg-calcite, a carbonate mineral, constitutes Ca precipitates produced ...

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