scholarly journals The Water Channel Aquaporin-8 Is Mainly Intracellular in Rat Hepatocytes, and Its Plasma Membrane Insertion Is Stimulated by Cyclic AMP

2001 ◽  
Vol 276 (15) ◽  
pp. 12147-12152 ◽  
Author(s):  
Fabiana Garcı́a ◽  
Arlinet Kierbel ◽  
M. Cecilia Larocca ◽  
Sergio A. Gradilone ◽  
Patrick Splinter ◽  
...  
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Plasma Membranes ◽  
Water Channel ◽  
Rat Hepatocytes ◽  
Immunoblot Analysis ◽  
Subcellular Fractionation ◽  
Bile Secretion ◽  
Confocal Immunofluorescence Microscopy ◽  
Microsomal Membranes

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected anN-glycosylated band of ∼34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt2cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt2cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt2cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.

Association of kinesin with the Golgi apparatus in rat hepatocytes

1994 ◽  
Vol 107 (9) ◽  
pp. 2417-2426 ◽  
Author(s):  
D.L. Marks ◽  
J.M. Larkin ◽  
M.A. McNiven
Keyword(s):  
Golgi Apparatus ◽  
Immunofluorescence Microscopy ◽  
Rat Hepatocytes ◽  
Cell Types ◽  
Immunoblot Analysis ◽  
Subcellular Fractionation ◽  
Rat Hepatocyte ◽  
Membranous Structure ◽  
Microtubule Disruption ◽  
Motor Enzymes

The Golgi apparatus is a dynamic membranous structure, which has been observed to alter its location and morphology during the cell cycle and after microtubule disruption. These dynamics are believed to be supported by a close structural interaction of the Golgi with the microtubule cytoskeleton and associated motor enzymes. One microtubule-dependent motor enzyme, kinesin, has been implicated in Golgi movement and function although direct evidence supporting this interaction is lacking. In this study, we utilized two well-characterized kinesin antibodies in conjunction with subcellular fractionation techniques, immunoblot analysis and immunofluorescence microscopy to conduct a detailed study on the association of kinesin with the Golgi and other membranous organelles in a polarized epithelial cell, the primary rat hepatocyte. We found that kinesin represents approximately 0.3% of total protein in rat liver homogenates, with approximately 30% membrane-associated and the remainder in the cytosol. Among membrane fractions, kinesin was concentrated markedly in Golgi-enriched fractions, which were prepared using two independent techniques. Kinesin was also abundant in fractions enriched in transcytotic carriers and secretory vesicles, with lower levels detected on fractions enriched in endosomes, endoplasmic reticulum, lysosomes and mitochondria. Immunofluorescence microscopy showed that kinesin is concentrated on Golgi-like structures in both primary cultured hepatocytes and rat hepatocyte-derived clone 9 cells. Double-label immunofluorescence demonstrated that kinesin staining colocalizes with the Golgi marker, alpha-mannosidase II, in both cell types. These results provide compelling evidence showing that kinesin is associated with the Golgi complex in cells and implicate this motor enzyme in Golgi structure, function and dynamics.

scholarly journals Immunoelectron microscope localization of cytochrome P-450 on microsomes and other membrane structures of rat hepatocytes.

1978 ◽  
Vol 78 (2) ◽  
pp. 503-519 ◽  
Author(s):  
S Matsuura ◽  
Y Fujii-Kuriyama ◽  
Y Tashiro
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membranes ◽  
Control Level ◽  
Rat Hepatocytes ◽  
Present Observation ◽  
Membrane Structures ◽  
Rat Liver Cells ◽  
Microsomal Membranes ◽  
Almost All ◽  
Cytochrome P 450

Localization of cytochrome P-450 on various membrane fractions of rat liver cells was studied by direct immunoelectron microscopy using ferritin-conjugated antibody to the cytochrome. The outer surfaces of almost all the microsomal vesicles were labeled with ferritin particles. The distribution of the particles on each microsomal vesicle was usually heterogeneous, indicating clustering of the cytochrome, and phenobarbital treatment markedly increased the labeled regions of the microsomal membranes. The outer nuclear envelopes were also labeled with ferritin particles, while on the surface of other membrane structures such as Golgi complexes, outer mitochondrial membranes and plasma membranes the labeling was scanty and at the control level. The present observation indicates that cytochrome P-450 molecules are localized exclusively on endoplasmic reticulum membranes and outer nuclear envelopes where they are probably distributed not uniformly but heterogeneously, forming clusters or patches. The physiological significance of such microheterogeneity in the distribution of the cytochrome on endoplasmic reticulum membranes is discussed.

scholarly journals Water Transport and Ion Diffusion Investigation of an Amphotericin B-Based Channel Applied to Forward Osmosis: A Simulation Study

Membranes ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 646
Author(s):  
Hao-Chen Wu ◽  
Tomohisa Yoshioka ◽  
Keizo Nakagawa ◽  
Takuji Shintani ◽  
Hideto Matsuyama
Keyword(s):  
Amphotericin B ◽  
Water Transport ◽  
Water Permeability ◽  
Salt Water ◽  
Water Channel ◽  
Forward Osmosis ◽  
Water Molecules ◽  
Ion Leakage ◽  
Channel Models ◽  
Water Permeation

The use of an Amphotericin B_Ergosterol (AmBEr) channel as an artificial water channel in forward osmosis filtration (FO) was studied via molecular dynamics (MD) simulation. Three channel models were constructed: a common AmBEr channel and two modified C3deOAmB_Ergosterol (C3deOAmBEr) channels with different diameters (12 Å and 18 Å). During FO filtration simulation, the osmotic pressure of salt-water was a driving force for water permeation. We examined the effect of the modified C3deOAmBEr channel on the water transport performance. By tracing the change of the number of water molecules along with simulation time in the saltwater region, the water permeability of the channel models could be calculated. A higher water permeability was observed for a modified C3deOAmBEr channel, and there was no ion permeation during the entire simulation period. The hydrated ions and water molecules were placed into the channel to explore the ion leakage behavior of the channels. The mean squared displacement (MSD) of ions and water molecules was obtained to study the ion leakage performance. The Amphotericin B-based channels showed excellent selectivity of water molecules against ions. The results obtained on an atomistic scale could assist in determining the properties and the optimal filtration applications for Amphotericin B-based channels.

Glucagon induces the gene expression of aquaporin-8 but not that of aquaporin-9 water channels in the rat hepatocyte

2009 ◽  
Vol 296 (4) ◽  
pp. R1274-R1281 ◽  
Author(s):  
Leandro R. Soria ◽  
Sergio A. Gradilone ◽  
M. Cecilia Larocca ◽  
Raúl A. Marinelli
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Rat Hepatocytes ◽  
Water Channels ◽  
Bile Secretion ◽  
Signal Pathways ◽  
Rat Hepatocyte ◽  
Confocal Immunofluorescence Microscopy ◽  
Aquaporin 9 ◽  
Additional Support

Glucagon stimulates the vesicle trafficking of aquaporin-8 (AQP8) water channels to the rat hepatocyte canalicular membranes, a process thought to be relevant to glucagon-induced bile secretion. In this study, we investigated whether glucagon is able to modulate the gene expression of hepatocyte AQP8. Glucagon was administered to rats at 0.2 mg/100 g body wt ip in 2, 3, or 6 equally spaced doses for 8, 16, and 36 h, respectively. Immunoblotting analysis showed that hepatic 34-kDa AQP8 was significantly increased by 79 and 107% at 16 and 36 h, respectively. Hepatic AQP9 protein expression remained unaltered. AQP8 mRNA expression, assessed by real-time PCR, was not modified over time, suggesting a posttranscriptional mechanism of AQP8 protein increase. Glucagon effects on AQP8 were directly studied in primary cultured rat hepatocytes. Immunoblotting and confocal immunofluorescence microscopy confirmed the specific glucagon-induced AQP8 upregulation. The RNA polymerase II inhibitor actinomycin D was unable to prevent glucagon effect, providing additional support to the nontranscriptional upregulation of AQP8. Cycloheximide also showed no effect, suggesting that glucagon-induced AQP8 expression does not depend on protein synthesis but rather on protein degradation. Inhibitory experiments suggest that a reduced calpain-mediated AQP8 proteolysis could be involved. The action of glucagon on hepatocyte AQP8 was mimicked by dibutyryl cAMP and suppressed by PKA or phosphatidylinositol-3-kinase (PI3K) inhibitors. In conclusion, our data suggest that glucagon induces the gene expression of rat hepatocyte AQP8 by reducing its degradation, a process that involves cAMP-PKA and PI3K signal pathways.

Defective hepatocyte aquaporin-8 expression and reduced canalicular membrane water permeability in estrogen-induced cholestasis

2007 ◽  
Vol 292 (3) ◽  
pp. G905-G912 ◽  
Author(s):  
Flavia I. Carreras ◽  
Guillermo L. Lehmann ◽  
Domenico Ferri ◽  
Mariana F. Tioni ◽  
Giuseppe Calamita ◽  
...  
Keyword(s):  
Water Permeability ◽  
Protein Level ◽  
Intrahepatic Cholestasis ◽  
Rat Hepatocytes ◽  
Functional Expression ◽  
Bile Secretion ◽  
Northern Blotting ◽  
Bile Formation ◽  
Canalicular Membrane ◽  
Lysosomal Protease

Our previous work supports a role for aquaporin-8 (AQP8) water channels in rat hepatocyte bile formation mainly by facilitating the osmotically driven canalicular secretion of water. In this study, we tested whether a condition with compromised canalicular bile secretion, i.e., the estrogen-induced intrahepatic cholestasis, displays defective hepatocyte AQP8 functional expression. After 17α-ethinylestradiol administration (5 mg·kg body wt−1·day−1 for 5 days) to rats, the bile flow was reduced by 58% ( P < 0.05). By subcellular fractionation and immunoblotting analysis, we found that 34 kDa AQP8 was significantly decreased by ∼70% in plasma (canalicular) and intracellular (vesicular) liver membranes. However, 17α-ethinylestradiol-induced cholestasis did not significantly affect the protein level or the subcellular localization of sinusoidal AQP9. Immunohistochemistry for liver AQPs confirmed these observations. Osmotic water permeability ( Pf) of canalicular membranes, measured by stopped-flow spectrophotometry, was significantly reduced (73 ± 1 vs. 57 ± 2 μm/s) in cholestasis, consistent with defective canalicular AQP8 functional expression. By Northern blotting, we found that AQP8 mRNA expression was increased by 115% in cholestasis, suggesting a posttranscriptional mechanism of protein level reduction. Accordingly, studies in primary cultured rat hepatocytes indicated that the lysosomal protease inhibitor leupeptin prevented the estrogen-induced AQP8 downregulation. In conclusion, hepatocyte AQP8 protein expression is downregulated in estrogen-induced intrahepatic cholestasis, presumably by lysosomal-mediated degradation. Reduced canalicular membrane AQP8 expression is associated with impaired osmotic membrane water permeability. Our data support the novel notion that a defective expression of canalicular AQP8 contributes as a mechanism for bile secretory dysfunction of cholestatic hepatocytes.

Aquaporin-3 water channel localization and regulation in rat kidney

1995 ◽  
Vol 269 (5) ◽  
pp. F663-F672 ◽  
Author(s):  
C. A. Ecelbarger ◽  
J. Terris ◽  
G. Frindt ◽  
M. Echevarria ◽  
D. Marples ◽  
...  
Keyword(s):  
High Speed ◽  
Plasma Membranes ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Water Channel ◽  
Subcellular Fractionation ◽  
Aquaporin 3 ◽  
Immunofluorescence Studies ◽  
Intracellular Vesicles ◽  
Collecting Duct Epithelium

The aquaporins are a family of water channels expressed in several water-transporting tissues, including the kidney. We have used a peptide-derived, affinity-purified polyclonal antibody to aquaporin-3 (AQP-3) to investigate its localization and regulation in the kidney. Immunoblotting experiments showed expression in both renal cortex and medulla, with greatest expression in the base of the inner medulla. Subcellular fractionation of membranes, using progressively higher centrifugation speeds, revealed that AQP-3 is present predominantly in the 4,000 and 17,000 g pellets and, in contrast to AQP-2, is virtually absent in the high-speed (200,000 g) pellet that contains small intracellular vesicles. Immunocytochemistry and immunofluorescence studies revealed that labeling is restricted to the cortical, outer medullary, and inner medullary collecting ducts. Within the collecting duct, principal cells were labeled, whereas intercalated cells were unlabeled. Consistent with previous immunofluorescence studies (K. Ishibashi, S. Sasaki, K. Fushimi, S. Uchida, M. Kuwahara, H. Saito, T. Furukawa, K. Nakajima, Y. Yamaguchi, T. Gojobori, and F. Marumo. Proc. Natl. Acad. Sci. USA 91: 6269-6273, 1994; T. Ma, A. Frigeri, H. Hasegawa, and A. S. Verkman. J. Biol. Chem. 269: 21845-21849, 1994), the labeling was confined to the basolateral domain. Immunoelectron microscopy, using the immunogold technique in ultrathin cryosections, demonstrated a predominant labeling of the basolateral plasma membranes. In contrast to previous findings with AQP-2, there was only limited AQP-3 labeling of intracellular vesicles, suggesting that this water channel is not regulated acutely through vesicular trafficking. Immunoblotting studies revealed that thirsting of rats for 48 h approximately doubled the amount of AQP-3 protein in the inner medulla. These studies are consistent with a role for AQP-3 in osmotically driven water absorption across the collecting duct epithelium and suggest that the expression of AQP-3 is regulated on a long-term basis.

Imidazole derivatives as artificial water channel building-blocks: structural design influence on water permeability

2018 ◽  
Vol 209 ◽  
pp. 113-124 ◽  
Author(s):  
Zhanhu Sun ◽  
Istvan Kocsis ◽  
Yuhao Li ◽  
Yves-Marie Legrand ◽  
Mihail Barboiu
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Structural Design ◽  
Water Channel ◽  
Building Blocks ◽  
Structural Modifications ◽  
Imidazole Derivatives ◽  
Permeability Variation ◽  
Self Assembled ◽  
Artificial Water

A series of mono- and di-ureidoethylimidazole derivatives were tested as self-assembled supramolecular channels for water transport across a vesicle bilayer. Structural modifications of the selected compounds were related to permeability variation.

scholarly journals Aquaporin-4–dependent K+ and water transport modeled in brain extracellular space following neuroexcitation

2012 ◽  
Vol 141 (1) ◽  
pp. 119-132 ◽  
Author(s):  
Byung-Ju Jin ◽  
Hua Zhang ◽  
Devin K. Binder ◽  
A.S. Verkman
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Extracellular Space ◽  
Water Channel ◽  
Aquaporin 4 ◽  
Solute Diffusion ◽  
Water Transport Properties ◽  
And Diffusion ◽  
K Permeability ◽  
Brain Extracellular Space

Potassium (K+) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K+] accumulation and slowing K+ reuptake. These effects could involve AQP4-dependent: (a) K+ permeability, (b) resting ECS volume, (c) ECS contraction during K+ reuptake, and (d) diffusion-limited water/K+ transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K+ and water uptake into astrocytes after neuronal release of K+ into the ECS. The model computed the kinetics of ECS [K+] and volume, with input parameters including initial ECS volume, astrocyte K+ conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte–ECS interface. The modeling showed that mechanisms b–d, together, can predict experimentally observed impairment in K+ reuptake from the ECS in AQP4 deficiency, as well as altered K+ accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K+/water coupling in the ECS without requiring AQP4-dependent astrocyte K+ permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency.

scholarly journals Tetrameric assembly of CHIP28 water channels in liposomes and cell membranes: a freeze-fracture study.

1993 ◽  
Vol 123 (3) ◽  
pp. 605-618 ◽  
Author(s):  
J M Verbavatz ◽  
D Brown ◽  
I Sabolić ◽  
G Valenti ◽  
D A Ausiello ◽  
...  
Keyword(s):  
Water Permeability ◽  
Cho Cells ◽  
Cell Membranes ◽  
Plasma Membranes ◽  
Single Channel ◽  
Water Channel ◽  
Freeze Fracture ◽  
Water Channels ◽  
Straight Tubules ◽  
Tetrameric Assembly

Channel forming integral protein of 28 kD (CHIP28) functions as a water channel in erythrocytes, kidney proximal tubule and thin descending limb of Henle. CHIP28 morphology was examined by freeze-fracture EM in proteoliposomes reconstituted with purified CHIP28, CHO cells stably transfected with CHIP28k cDNA, and rat kidney tubules. Liposomes reconstituted with HPLC-purified CHIP28 from human erythrocytes had a high osmotic water permeability (Pf0.04 cm/s) that was inhibited by HgCl2. Freeze-fracture replicas showed a fairly uniform set of intramembrane particles (IMPs); no IMPs were observed in liposomes without incorporated protein. By rotary shadowing, the IMPs had a diameter of 8.5 +/- 1.3 nm (mean +/- SD); many IMPs consisted of a distinct arrangement of four smaller subunits surrounding a central depression. IMPs of similar size and appearance were seen on the P-face of plasma membranes from CHIP28k-transfected (but not mock-transfected) CHO cells, rat thin descending limb (TDL) of Henle, and S3 segment of proximal straight tubules. A distinctive network of complementary IMP imprints was observed on the E-face of CHIP28-containing plasma membranes. The densities of IMPs in the size range of CHIP28 IMPs, determined by non-linear regression, were (in IMPs/microns 2): 2,494 in CHO cells, 5,785 in TDL, and 1,928 in proximal straight tubules; predicted Pf, based on the CHIP28 single channel water permeability of 3.6 x 10(-14) cm3/S (10 degrees C), was in good agreement with measured Pf of 0.027 cm/S, 0.075 cm/S, and 0.031 cm/S, respectively, in these cell types. Assuming that each CHIP28 monomer is a right cylindrical pore of length 5 nm and density 1.3 g/cm3, the monomer diameter would be 3.2 nm; a symmetrical arrangement of four cylinders would have a greatest diameter of 7.2 nm, which after correction for the thickness of platinum deposit, is similar to the measured IMP diameter of approximately 8.5 nm. These results provide a morphological signature for CHIP28 water channels and evidence for a tetrameric assembly of CHIP28 monomers in reconstituted proteoliposomes and cell membranes.

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