Expression and immunolocalization of the aquaporin-8 water channel in rat gastrointestinal tract

Calamita, Giuseppe; Mazzone, Amelia; Bizzoca, Antonella; Cavalier, Annie; Cassano, Grazia; Thomas, Daniel; Svelto, María

doi:10.1078/0171-9335-00210

Cited by 116 publications

(99 citation statements)

References 36 publications

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“…4). As observed previously, 6,10 normal livers showed a punctate, intracellular staining in hepatocytes. Canalicular plasma membrane staining was obscured by the strong intracellular signal (Fig.…”

Section: Resultssupporting

confidence: 59%

“…[3][4][5][6][7][8][9][10] AQP8, which seems to be the most abundant AQP in hepatocytes, is predominantly localized in intracellular vesicles; its translocation to the canalicular plasma membrane is microtubule dependent and adenosine 3Ј,5Ј-cyclic monophosphate (cAMP) stimulated. 5,6,10 AQP9 resides exclusively on the sinusoidal plasma membranes of hepatocytes and thereby may facilitate the movement of water and certain small solutes. 4,10 AQP0 is localized intracellularly, and its significance in hepatocytes is currently unclear.…”

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confidence: 99%

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Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis

Carreras

2003

Hepatology

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Hepatocytes express the water channel aquaporin-8 (AQP8), which is mainly localized in intracellular vesicles, and its adenosine 3 ,5 -cyclic monophosphate (cAMP)-induced translocation to the plasma membrane facilitates osmotic water movement during canalicular bile secretion. Thus, defective expression of AQP8 may be associated with secretory dysfunction of hepatocytes caused by extrahepatic cholestasis. We studied the effect of 1, 3, and 7 days of bile duct ligation (BDL) on protein expression, subcellular localization, and messenger RNA (mRNA) levels of AQP8; this was determined in rat livers by immunoblotting in subcellular membranes, light immunohistochemistry, immunogold electron microscopy, and Northern blotting. One day of BDL did not affect expression or subcellular localization of AQP8. Three days of BDL reduced the amount of intracellular AQP8 (75%; P < .001) without affecting its plasma membrane expression. Seven days after BDL, AQP8 was markedly decreased in intracellular (67%; P < .05) and plasma (56%; P < .05) membranes. Dibutyryl cAMP failed to increase AQP8 in plasma membranes from liver slices, suggesting a defective translocation of AQP8 in 7-day BDL rats. Immunohistochemistry and immunoelectron microscopy in liver sections confirmed the BDLinduced decreased expression of hepatocyte AQP8 in intracellular vesicles and canalicular membranes. AQP8 mRNA expression was unaffected by 1-day BDL but was significantly increased by about 200% in 3-and 7-day BDL rats, indicating a posttranscriptional mechanism for protein level reduction. In conclusion, BDL-induced extrahepatic cholestasis caused posttranscriptional downregulation of hepatocyte AQP8 protein expression. Defective expression of AQP8 water channels may contribute to bile secretory dysfunction of cholestatic hepatocytes.

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Section: Resultssupporting

confidence: 59%

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confidence: 99%

Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis

Carreras

2003

Hepatology

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“…When expressed in Xenopus oocytes, mouse, rat or human aquaporin 8 genes increase the water permeability of oocytes by 10 to 20 fold. In addition, the cytoplasmic localization of AQP8 may also hint at its involvement in intracellular osmoregulation [9] . Subsequent studies [10][11][12][13][14][15][16] have shown that AQP8 has a wide tissue distribution in mammals, with expression noted in the testis, kidney, heart, gastrointestinal tract, airway, salivary gland, pancreas and placenta.…”

Section: Introductionmentioning

confidence: 99%

“…There are currently 13 known mammalian aquaporins (AQP0-12); a subset of these molecules are capable of increasing the permeability of small molecules such as glycerol (AQP3, 7, 9) and urea (AQP3, 7,8,9). AQP8 is reportedly permeable to ammonia [3] .…”

Section: Introductionmentioning

confidence: 99%

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Pregnant phenotype in aquaporin 8-deficient mice

et al. 2011

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Aim: Aquaporin 8 (AQP8) is expressed within the female reproductive system but its physiological function reminds to be elucidated. This study investigates the role of AQP8 during pregnancy using AQP8-knockout (AQP8-KO) mice. Methods: Homozygous AQP8-KO mice were mated, and the conception rate was recorded. AQP8-KO pregnant mice or their offspring were divided into 5 subgroups according to fetal gestational day (7, 13, 16, 18 GD) and newborn. Wild type C57 pregnant mice served as the control group. The number of pregnant mice, total embryos and atrophic embryos, as well as fetal weight, placental weight and placental area were recorded for each subgroup. The amount of amniotic fluid in each sac at 13, 16, and 18 GD was calculated. Statistical significance was determined by analysis of variance of factorial design and chi-square tests. Results: Conception rates did not differ significantly between AQP8-KO and wild type mice. AQP8-KO pregnant mice had a significantly higher number of embryos compared to wild type controls. Fetal/neonatal weight was also significantly greater in the AQP8-KO group compared to age-matched wild type controls. The amount of amniotic fluid was greater in AQP8-KO pregnant mice than wild type controls, although the FM/AFA (fetal weight/amniotic fluid amount) did not differ. While AQP8-KO placental weight was significantly larger than wild type controls, there was no evidence of placental pathology in either group. Conclusion: The results suggest that AQP8 deficiency plays an important role in pregnancy outcome.

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Sponge Biosilica Formation Involves Syneresis Following Polycondensation in vivo

Wang¹,

Schröder²,

Brandt³

et al. 2011

ChemBioChem

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Syneresis is a process observed during the maturation/aging of silica gels obtained by sol-gel synthesis that results in shrinkage and expulsion of water due to a rearrangement and increase in the number of bridging siloxane bonds. Here we describe how the process of biosilica deposition during spicule ("biosilica" skeleton of the siliceous sponges) formation involves a phase of syneresis that occurs after the enzyme-mediated polycondensation reaction. Primmorphs from the demosponge Suberites domuncula were used to study syneresis and the inhibition of this mechanism. We showed by scanning electron microscopy that spicules added to primmorphs that have been incubated with manganese sulfate fuse together through the deposition of silica spheres and bridges. Energy-dispersive X-ray mapping of the newly formed deposits showed high silicon and oxygen content. These biosilica deposits contain a comparably higher percentage of water than mature/aged spicules. Quantitative real-time polymerase chain reaction analyses revealed that the addition of silicate to primmorph cultures resulted in a marked upregulation of the expression of the aquaporin gene and of the genes encoding the silica anabolic enzyme silicatein-α and the silica catabolic enzyme silicase. On the other hand, addition of manganese sulfate, either alone or together with silicate, caused a strong reduction in the level of aquaporin transcripts, although this metal ion did not essentially affect the silicate-induced increase in silicatein-α and silicase gene expression. We conclude that the secondary silica deposits formed on spicules under physiological conditions in the presence of silicate fuse together and subsequently undergo syneresis, which is facilitated by the removal of water through aquaporin channels. In growing spicules, these processes of biosilica formation and syneresis in the lamellar monolithic structures precede the final step of "biosintering" during which the massive biosilica rods of the spicules are formed.

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Expression and immunolocalization of the aquaporin-8 water channel in rat gastrointestinal tract

Cited by 116 publications

References 36 publications

Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis

Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis

Pregnant phenotype in aquaporin 8-deficient mice

Sponge Biosilica Formation Involves Syneresis Following Polycondensation in vivo

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