Expression and functional characterization of four aquaporin water channels from the European eel ( Anguilla anguilla )

We investigated the salinity-dependent expression dynamics of seven aquaporin paralogs (aqp1a, aqp3a, aqp7, aqp8ab, aqp10a, aqp10b and aqp11a) in several tissues of euryhaline Japanese medaka (Oryzias latipes). All paralogs except aqp7 and aqp10a had a broad tissue distribution, and several were affected by salinity in both osmoregulatory and non-osmoregulatory tissues. In the intestine, aqp1a, aqp7, aqp8ab and aqp10a decreased upon seawater (SW) acclimation in both long-term acclimated fish and during 1-3 days of the transition period. In the gill, aqp3a was lower and aqp10a higher in SW than in freshwater (FW). In the kidney no aqps were affected by salinity. In the skin, aqp1a and aqp3a were lower in SW than in FW. In the liver, aqp8ab and aqp10a were lower in SW than in FW. Furthermore, six Na + ,K + -ATPase α-subunit isoform transcripts were analysed in the intestine but none showed a consistent response to salinity, suggesting that water transport is not regulated at this level. In contrast, mRNA of the Na + ,K + ,2Cl --cotransporter type-2 strongly increased in the intestine in SW compared with FW fish. Using custom-made antibodies, Aqp1a, Aqp8ab and Aqp10a were localized in the apical region of enterocytes of FW fish. Apical staining intensity strongly decreased, vanished or moved to subapical regions, when fish were acclimated to SW, supporting the lower mRNA expression in SW. Western blots confirmed the decrease in Aqp1a and Aqp10a in SW. The strong decrease in aquaporin expression in the intestine of SW fish is surprising, and challenges the paradigm for transepithelial intestinal water absorption in SW fishes.

Section: Research Articlementioning

confidence: 99%

Aquaporin expression in the Japanese medaka (Oryzias latipes, Temminck & Schlegel) in FW and SW: challenging the paradigm for intestinal water transport?

Madsen

Bujak

Tipsmark

2014

“…To test the effect of HgCl 2 on swelling rate, vesicles were exposed to artificial seawater (ASW; 545 mmol l −1 NaCl), SSW and distilled water buffered with 5.0 mmol l −1 Tris under control conditions and after treatment with 1 mmol l −1 HgCl 2 (MacIver et al, 2009).…”

Section: Triton X-100 and Hgcl 2 Exposurementioning

confidence: 99%

Defensive slime formation in Pacific hagfish requires Ca2+ and aquaporin mediated swelling of released mucin vesicles

Herr

Clifford

Goss

et al. 2014

Hagfishes defend themselves from fish predators via the rapid deployment of a fibrous slime that adheres to and clogs gills. The slime transforms from a thick glandular exudate to a fully hydrated product in a fraction of a second through a process that involves the swelling and rupture of numerous mucin vesicles. Here we demonstrate that the vesicle membrane plays an important role in regulating the swelling of mucin granules, and provide evidence that the membrane contains proteins that facilitate the movement of ions and water molecules. By exposing isolated mucin vesicles to varying combinations of inorganic ions, organic compounds and membrane channel inhibitors, we found that the majority of hagfish mucin vesicles require Ca 2+ to rupture. We also show that Ca 2+-dependent rupture can be pharmacologically inhibited, which suggests a role for Ca 2+ -activated membrane transporters. We demonstrate that the aquaporin inhibitor mercuric chloride reduces the rate of vesicle swelling by an order of magnitude, which suggests that aquaporins facilitate the influx of water during vesicle deployment. Molecular evidence of two aquaporin homologues expressed in the slime glands further supports this idea. We propose a model of hagfish slime mucin vesicle rupture that involves Ca 2+ -activated transporters and aquaporins, and suggest that the presence of these proteins is an adaptation for increasing the speed of vesicle rupture and, consequently, the speed of the sliming response of hagfishes.

“…Observations of elevated mRNA expression following seawater transfer, elevated AQP1 protein abundance in intestinal tissue following seawater acclimation and, finally, apical as well as basolateral localization of the protein suggest a role in transepithelial water movement (Aoki et al, 2003;Martinez et al, 2005a;Martinez et al, 2005b;Raldua et al, 2008). It has been demonstrated that AQP1 genes from fish confer water permeability in expression systems (MacIver et al, 2009), including AQP1a from F. heteroclitus (Tingaud-Sequeira et al, 2009), but despite the above observations, direct evidence for a role for AQP1 in intestinal water absorption has been lacking. Consistent with this view, Cerda and Finn caution that the relative contribution of aquaporin-mediated transcellular flux versus paracellular flux is largely unknown (Cerda and Finn, 2010).…”

Section: A Role For Aquaporins In Intestinal Water Absorption In Fishmentioning

confidence: 99%

“…, the same as that required to inhibit fish aquaporins in an oocyte expression system (MacIver et al, 2009). However, 10…”

Section: A Role For Aquaporins In Intestinal Water Absorption In Fishmentioning

confidence: 99%

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

Wood

Grosell

2012

SUMMARYParacellular permeability and absorptive water flux across the intestine of the euryhaline killifish were investigated using in vitro gut sac preparations from seawater-and freshwater-acclimated animals. The permeability of polyethylene glycol (PEG), a wellestablished paracellular probe, was measured using trace amounts of radiolabelled oligomers of three different molecular sizes (PEG-400, PEG-900 and PEG-4000) at various times after satiation feeding. All three PEG molecules were absorbed, with permeability declining as a linear function of increasing hydrodynamic radius. Response patterns were similar in seawater and freshwater preparations, though water absorption and PEG-900 permeability were greater in the latter. Despite up to 4-fold variations in absorptive water flux associated with feeding and fasting (highest at 1-3h, lowest at 12-24h and intermediate at 1-2weeks post-feeding), there were no changes in PEG permeability for any size oligomer. When PEG permeability was measured in the opposite direction (i.e. serosal to mucosal) from net water flux, it was again unchanged. HgCl 2 (10 -3 moll -1 ), a putative blocker of aquaporins, eliminated absorptive water flux yet increased PEG-4000 permeability by 6-to 8-fold in both freshwater and seawater preparations. Experimentally raising the serosal osmolality by addition of 300mmoll -1 mannitol increased the absorptive water flux rate 10-fold, but did not alter PEG permeability. Under these conditions, HgCl 2 reduced absorptive water flux by 60% and again increased PEG permeability by 6-to 8-fold in both freshwater and seawater preparations. Clearly, there was no influence of solvent drag on PEG movement. The putative paracellular blocker 2,4,6-triaminopyrimidine (TAP, 20mmoll -1 ) had no effect on net water flux or PEG permeability. We conclude that PEG and water move by separate pathways; absorptive water transport probably occurs via a transcellular route in the intestine of Fundulus heteroclitus.