The mechanism of salt and water absorption in the intestine of the eel (Anguilla anguilla) adapted to waters of various salinities

Abstract

SUMMARY1. The absorption of NaCi and water was studied by intraluminal in vivo perfusion of the intestine of the yellow European eel (Anguilla anguilla) adapted to fresh water (FW), to sea water (SW), and to double strength SW (DSW).2. The net lumen to plasma NaCl transport from diluted SW perfusion fluids was independent of the NaCl concentration in the Na+ concentration range tested. The NaCl absorption (expressed as ,t-equiv/100 g . hr.) increased from FW (mean +S.E.): Na+ 166+ 17, Cl-205+ 24 to SW: Na+ 363 + 33, Cl-423 + 37, and again in DSW: Na+ 640 + 110, C1-676 + 149.3. The osmolality of the perfusion fluid which resulted in zero net water transport was higher than plasma osmolality by 73 + 3 m-osmole in FW, 126 + 5 m-osmole in SW, and 244 + 32 m-osmole in DSW (mean + s.E.). A fairly constant ratio between net NaCl transport and this osmolality difference prevailed.4. The general osmotic permeability to water in the serosa-mucosa direction (expressed as ,al./100g.hr.m-osmole) measured from experiments with impermeant solute increased from FW: 3-7 + 0-5 to SW: 7-2 + 1.0 (mean + S.E.).5. These results are compatible with the interpretation that the water flow occurring in the absence of a general transmural osmotic gradient, the 'solute-linked water flow', is linearly related both to net NaCl transport and to the osmotic permeability to water. The findings support the view that the 'solute-linked water flow' is, indeed, secondary to the salt movement and is due to osmotic force.

Independence of net water flux from paracellular permeability in the intestine ofFundulus heteroclitus, a euryhaline teleost

“…Notably, the Cl -concentration of the absorbate increases with time of fasting, as would be predicted if there is a mechanism to control how much water flux follows ion flux through the transcellular pathway. Interestingly, the only other euryhaline teleost that is known to rely on intestinal rather than branchial Cl -uptake in freshwater is the eel (Kirsch, 1972;Grosell et al, 2000), and here too the concentration of the absorbate was higher in freshwater than in seawater animals (Skadhauge, 1969). Additional experiments (Skadhauge, 1969;Skadhauge, 1974) demonstrated that the intestinal water absorption in the eel was closely linked to, and presumably driven by, the active transport of Na + and Cl -, though the author suggested that this might occur via the lateral intercellular spaces (i.e.…”

Adaptation to different salinities exposes functional specialization in the intestine of the sea bream (Sparus aurata L.)

“…Effects of salinity have been shown in eels, where the intestinal water absorption in seawater animals is far higher than in freshwater animals (Aoki et al, 2003;Kim et al, 2008;Skadhauge, 1969). At the molecular level, the water absorption mechanisms in the intestine of marine fish are driven by NaCl via an apical Na…”

The role of the rectum in osmoregulation and the potential effect of renoguanylin on SLC26a6 transport activity in the Gulf toadfish (Opsanus beta)

“…To compensate for this, seawater teleosts drink copious volumes of water that are continually desalinated by the esophagus and gastrointestinal tract to produce a fluid that is roughly isotonic to blood plasma (17, 34). The constant absorption of ions, by the intestine, is critical as it lowers luminal osmolality and allows for solute-coupled water absorption, and, thereby, compensating for branchial water loss (45,46 (53), a process coupled to the ion transport mechanisms described above. The seawater teleost rectum also plays a role in water absorption.…”