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Results for “OSMOSIS AND PERMEABILITY”

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At least 433 records · Page 24Linked to original sources

PubMed2002

Unimpaired osmotic water permeability and fluid secretion in bile duct epithelia of AQP1 null mice.

The mechanisms by which fluid moves across the luminal membrane of cholangiocyte epithelia are uncertain. Previous studies suggested that aquaporin-1 (AQP1) is an important determinant of water movement in rat cholangiocytes and that cyclic AMP mediates the movement of these water channels from cytoplasm to apical membrane, thereby increasing the osmotic water permeability. To test this possibility we measured agonist-stimulated fluid secretion and osmotically driven water transport in isolated bile duct units (IBDUs) from AQP1 wild-type (+/+) and null (-/-) mice. AQP1 expression was confirmed in a mouse cholangiocyte cell line and +/+ liver. Forskolin-induced fluid secretion, measured from the kinetics of IBDU luminal expansion, was 0.05 fl/min and was not impaired in -/- mice. Osmotic water permeability (P(f)), measured from the initial rate of IBDU swelling in response to a 70-mosM osmotic gradient, was 11.1 x 10(-4) cm/s in +/+ mice and 11.5 x 10(-4) cm/s in -/- mice. P(f) values increased by approximately 50% in both +/+ and -/- mice following preincubation with forskolin. These findings provide direct evidence that AQP1 is not rate limiting for water movement in mouse cholangiocytes and does not appear to be regulated by cyclic AMP in this species.

Animals↗

PubMed1994

Atrial natriuretic peptide inhibited the natriferic and hydrosmotic effects of arginine vasotocin on toad skin.

The effect of rat atrial natriuretic peptide (rANP) on hormonal stimulated osmotic water permeability (Jw, hydrosmotic effect) and net ion transport (short-circuit current, SCC, natriferic effect) was studied on toad skin, a tissue with functional similarities to the mammalian distal nephron, in order to assess actions on transport mechanisms. Rat atrial natriuretic peptide, rANP-99-126 (rANP) inhibited stimulated SCC and Jw to submaximal concentrations of arginine vasotocin (AVT) at a site before cyclic AMP generation. The angiotensin-converting enzyme inhibitor (ACEI) MK-422 did not modify the inhibitory effect of ANP in the stimulated Jw.

Animals↗

PubMed1994

The effect of adrenalectomy on water permeability in rat papillary collecting duct.

1. Chronic adrenal insufficiency impairs maximal urine concentration, probably in part due to reduced medullary tonicity but also possibly by inhibition of distal nephron water transport. This latter defect has been demonstrated in rabbit but not in rat. 2. Since the time between adrenalectomy and experiment was different in rabbit and rat studies, diffusional water permeability was evaluated in the papillary collecting duct in the absence and presence of submaximal (20 microU/mL) and supramaximal (200 microU/mL) arginine vasopressin (AVP) in adrenalectomized rats at 7, 14 and 21 days. 3. Experimentation 7 days after adrenalectomy failed to demonstrate significantly altered basal or AVP-induced water permeability which increased by 23 and 78% with submaximal and supramaximal concentrations, respectively. Submaximal AVP concentrations also induced a comparable change in water permeability in adrenalectomized rats at 14 days; however, 21 days after adrenalectomy, diffusional water permeability was not increased by 20 microU/mL AVP (3.31 +/- 0.22 to 3.31 +/- 0.24 microns/s). Nevertheless, the effect of a supramaximal AVP concentration (200 microU/mL) was not altered by adrenalectomy (4.54 +/- 0.39 to 8.08 +/- 0.96; P < 0.01). Incubation of collecting ducts in aldosterone for 2 h did not reverse the inhibitory effect of chronic adrenalectomy on AVP-stimulated water transport. 4. These studies suggest that mineralocorticoid withdrawal does impair the hydro-osmotic action of AVP in the rat papillary collecting duct but that this effect takes between 14 and 21 days to occur.

Adrenal Glands↗

PubMed2000

Molecular mechanisms of action of prostaglandin E2 in the regulation of water osmotic permeability.

The functional role and molecular mechanisms of action of prostaglandin E2 (PGE2) in the regulation of water osmotic permeability in osmoregulatory epithelia (mammalian collecting tubules and amphibian urinary bladder) are considered. The paper describes the modern classification of PGE2 receptors, their distribution along a nephron and receptor-coupled intracellular second messenger systems. The mechanism of the inhibitory action of PGE2 on the antidiuretic hormone-induced enhancement of water osmotic permeability is analyzed. Special attention is given to the role of PGE2 as an auto- or paracrine regulator of water osmotic permeability in the phenomenon of ADH-independent increase of water permeability observed in an isolated amphibian urinary bladder in replacements of the surrounding serous solution. It is concluded that the osmoregulatory epithelium is not only a place of the maximum level of PGE2 synthesis in the kidney but is also characterized by a great diversity of PGE2 receptor subtypes: EP1, EP2, EP3 and EP4 have been revealed in the mammalian collecting tubules. Such a diversity of PGE2 receptors is in a good agreement with different functional effects of PGE2 in the osmoregulatory epithelium. The data considered suggest that PGE2 is not less important in the regulation of water and ion transport in the osmoregulatory epithelium than antidiuretic hormone.

Adenylyl Cyclases↗

PubMed2001

Optical dysfunction of the crystalline lens in aquaporin-0-deficient mice.

Aquaporin-0 (AQP0), a water transport channel protein, is the major intrinsic protein (MIP) of lens fiber cell plasma membranes. Mice deficient in the gene for AQP0 (Aqp0, Mip) were generated from a library of gene trap embryo stem cells. Sequence analysis showed that the gene trap vector had inserted into the first exon of Aqp0, causing a null mutation as verified by RNA blotting and immunochemistry. At 3 wk of age (postnatal day 21), lenses from null mice (Aqp0(-/-)) contained polymorphic opacities, whereas lenses from heterozygous mice (Aqp0(+/-)) were transparent and did not develop frank opacities until approximately 24 wk of age. Osmotic water permeability values for Aqp0(+/-) and Aqp0(-/-) lenses were reduced to approximately 46% and approximately 20% of wild-type values, respectively, and the focusing power of Aqp0(+/-) lenses was significantly lower than that of wild type. These findings show that heterozygous loss of AQP0 is sufficient to trigger cataractogenesis in mice and suggest that this MIP is required for optimal focusing of the crystalline lens.

Age Factors↗

PubMed1973

Dynamics of glomerular ultrafiltration in the rat. IV. Determination of the ultrafiltration coefficient.

Pressures and flow rates were measured in accessible surface glomeruli of mutant Wistar rats under conditions deliberately designed to prevent achievement of filtration pressure equilibrium, that is, the equalization of transcapillary hydrostatic and oncotic pressures by the efferent end of the glomerulus as typically observed in the normal hydropenic rat. Disequilibrium was obtained at elevated levels of glomerular plasma flow (GPF) brought about by acute expansion of plasma volume with a volume of rat plasma equal to 5% of body weight. Glomerular hydrostatic and oncotic pressures measured at high GPF were used to calculate the ultrafiltration coefficient, K(f), the product of effective hydraulic permeability and surface area. GPF was then either lowered (by aortic constriction) or raised (by carotid occlusion) in order to examine the dependence of K(f) on GPF. The value of K(f) per glomerulus, 0.08 nl/(s.mm Hg), was found not to vary over an approximately twofold range of GPF. This finding, taken together with data from previous studies from this laboratory, leads us to conclude that plasma-flow dependence of glomerular filtration rate (GFR) results primarily from flow-induced changes in mean ultrafiltration pressure, rather than large changes in K(f).

Animals↗

PubMed2002

Two novel aquaporin-2 mutations responsible for congenital nephrogenic diabetes insipidus in Chinese families.

Mutations in the aquaporin-2 gene (AQP2), encoding the vasopressin-regulated water channel of the renal collecting duct, are responsible for the autosomal recessive or dominant forms of congenital nephrogenic diabetes insipidus. We describe two new families with normal hypotensive and coagulation responses following the administration of desamino-8-D-arginine AVP, a clinical suggestion of normal vasopressin-2 receptors. The patients were compound heterozygotes for point mutations at nucleotide position 170 (CAG to CCG; Q57P) and at position 299 (GGA to GTA; G100V) in exon 1 of the AQP2 gene. Expression of the G57P and G100V AQP2 proteins in Xenopus oocytes showed only 1.3-fold and 1.2-fold increase, respectively, in the water permeability in contrast to 8.0-fold increase in oocytes injected with wild-type cRNA. Immunoblots of oocyte lysate revealed the intensities of the 29-kDa bands were comparable among oocytes injected with wild-type and mutant cRNAs. Immunocytochemistry showed the plasma membrane was not stained in oocytes injected with cRNA of Q57P and of G100V. These results provide evidence that the Q57P and G100V mutations in congenital nephrogenic diabetes insipidus are attributable to the misrouting of AQP2.

Adult↗

PubMed2005

Channel-dependent permeation of water and glycerol in mouse morulae.

The cryosensitivity of mammalian embryos depends on the stage of development. Because permeability to water and cryoprotectants plays an important role in cryopreservation, it is plausible that the permeability is involved in the difference in the tolerance to cryopreservation among embryos at different developmental stages. In this study, we examined the permeability to water and glycerol of mouse oocytes and embryos, and tried to deduce the pathway for the movement of water and glycerol. The water permeability (L(P), microm min(-1) atm(-1)) of oocytes and four-cell embryos at 25 degrees C was low (0.63-0.70) and its Arrhenius activation energy (E(a), kcal/mol) was high (11.6-12.3), which implies that the water permeates through the plasma membrane by simple diffusion. On the other hand, the L(p) of morulae and blastocysts was quite high (3.6-4.5) and its E(a) was quite low (5.1-6.3), which implies that the water moves through water channels. Aquaporin inhibitors, phloretin and p-(chloromercuri) benzene-sulfonate, reduced the L(p) of morulae significantly but not that of oocytes. By immunocytochemical analysis, aquaporin 3, which transports not only water but also glycerol, was detected in the morulae but not in the oocytes. Accordingly, the glycerol permeability (P(GLY), x 10(-3) cm/min) of oocytes was also low (0.01) and its E(a) was remarkably high (41.6), whereas P(GLY) of morulae was quite high (4.63) and its E(a) was low (10.0). Aquaporin inhibitors reduced the P(GLY) of morulae significantly. In conclusion, water and glycerol appear to move across the plasma membrane mainly by simple diffusion in oocytes but by facilitated diffusion through water channel(s) including aquaporin 3 in morulae.

Animals↗

PubMed1994

Differential osmotic behavior of mammalian oocytes before and after maturation: a quantitative analysis using goat oocytes as a model.

This study shows that immature and mature goat oocytes respond differently to hyperosmotic stress; when exposed to a 1.5 M propanediol solution, immature oocytes manifest a higher osmotic stress than do mature oocytes. This is the consequence of both higher water permeability (133.9 +/- 15.2 vs 82.4 +/- 4.4 x 10(-3) cm/min) and lower propanediol permeability (0.87 +/- 0.03 vs 1.20 +/- 0.03 x 10(-3) cm/min at 20 degrees C) in the immature than in the mature stage. The difference of osmotic behavior between these two types of oocytes is abolished following exposure to cytochalasin D, a drug known to modify the cellular microfilament network. This result suggests differences in actin organization between the two types of oocyte, probably at the cortical level. Calculated values of the intracellular concentration of propanediol as a function of time of exposure show that propanediol rapidly permeates both types of oocyte and that the kinetics of intracellular concentration are lowered by cytochalasin treatment.

Actin Cytoskeleton↗

PubMed1987

Osmotic water permeability in glycoprotein containing liposomes.

The kinetics of osmotic water permeability in proteoliposomes containing alpha 1-acid glycoprotein was investigated by means of stopped-flow spectrophotometry. A biphasic time-course of scattered light with time was registered. The rate constants calculated from fits to an exponential function in the first phase were proportional to the final medium osmolarity. The apparent second order rate constants Kapp (Osm-1 sec-1) were determined at different glycoprotein concentrations in the original mixture for preparation of proteoliposomes. The value of Kapp at lipid:glycoprotein weight ratio = 1 was plotted in Arrhenius coordinates. The calculated activation energy for water permeation through the lipid bilayer suggests that eventual channel mechanism may be involved due to the presence of glycoprotein molecule in the liposomes.

Hypertonic Solutions↗

PubMed1979

Osmotic opening of the blood-brain barrier to methotrexate in the rat.

Osmotic opening of the blood-brain barrier in the rat, by intracarotid infusion of 1.6 molal (m) arabinose solution, increases cerebrovascular permeability to 3H-methotrexate by a factor of about seven. PA (product of permeability and capillary surface area) increases from a mean of 3.3 X 10(-5) sec-1 in brains of control rats to as much as 28 X 10(-5) sec-1 at the cerebral hemisphere ipsilateral to carotid infusion. If tracer is introduced into the carotid artery after osmotic treatment, brain uptake is increased by a net factor of 50 (a factor of 70 due to elevation of PA, multiplied by 7 due to infusion by the carotid route) as compared to uptake by normal, untreated brain with infusion into a peripheral vein. Osmotic barrier opening followed by carotid drug administration may be of use in experimental chemotherapy of nervous system disease.

Animals↗

PubMed2006

Cryoprotectant permeability of aquaporin-3 expressed in Xenopus oocytes.

It has been shown that aquaporin-3, a water channel, is expressed in mouse embryos. This type of aquaporin transports not only water but also neutral solutes, including cell-permeating cryoprotectants. Therefore, the expression of this channel may have significant influence on the survival of cryopreserved embryos. However, permeability coefficients of aquaporin-3 to cryoprotectants have not been determined except for glycerol. In addition, permeability coefficients under concentration gradients are important for developing and improving cryopreservation protocols. In this study, we examined the permeability of aquaporin-3 to various cryoprotectants using Xenopus oocytes. The permeability of aquaporin-3 to cryoprotectants was measured by the volume change of aquaporin-3 cRNA-injected oocytes in modified Barth's solution containing either 10% glycerol, 8% ethylene glycol, 10% propylene glycol, 1.5 M acetamide, or 9.5% DMSO (1.51-1.83 Osm/kg) at 25 degrees C. Permeability coefficients of aquaporin-3 for ethylene glycol and propylene glycol were 33.50 and 31.45 x 10(-3) cm/min, respectively, which were as high as the value for glycerol (36.13 x 10(-3) cm/min). These values were much higher than those for water-injected control oocytes (0.04-0.11 x 10(-3) cm/min). On the other hand, the coefficients for acetamide and DMSO were not well determined because the volume data were poorly fitted by the two parameter model, possibly because of membrane damage. To avoid this, the permeability for these cryoprotectants was measured under a low concentration gradient by suspending oocytes in aqueous solutions containing low concentrations of acetamide or DMSO dissolved in water (0.20 Osm/kg). The coefficient for acetamide (24.60 x 10(-3) cm/min) was as high as the coefficients for glycerol, ethylene glycol, and propylene glycol, and was significantly higher than the value for control (6.50 x 10(-3) cm/min). The value for DMSO (6.33 x 10(-3) cm/min) was relatively low, although higher than the value for control (0.79 x 10(-3) cm/min). This is the first reported observation of DMSO transport by aquaporin-3.

Animals↗

PubMed2005

Aquaporin-3 expressed in the basolateral membrane of gill chloride cells in Mozambique tilapia Oreochromis mossambicus adapted to freshwater and seawater.

We have cloned a homologue of mammalian aquaporin-3 (AQP3) from gills of Mozambique tilapia using a reverse transcription-polymerase chain reaction (RT-PCR). The deduced amino acid sequence shared 64-75% homology with other vertebrate AQP3 homologues. RT-PCR revealed that tilapia AQP3 was expressed in the brain, pituitary, kidney, spleen, intestine, skin, eye and gill in tilapia adapted to freshwater (FW) and seawater (SW). We also examined functional characteristics of tilapia AQP3 using Xenopus oocytes as an in vitro transcribed cRNA expression system. Osmotic water permeability (Pf) of Xenopus oocytes expressing tilapia AQP3 was about 30-fold higher than that of control oocytes, and was 80% inhibited by treatment with 0.3 mmol l(-1) HgCl2. Light-microscopic immunocytochemistry of branchial epithelia revealed that tilapia AQP3 was expressed in gill chloride cells of FW- and SW-adapted tilapia. Electron-microscopic immunocytochemistry further demonstrated that tilapia AQP3 was localized in the basolateral membrane of gill chloride cells. Basolateral localization of AQP3 in gill chloride cells suggests that AQP3 is involved in regulatory volume changes and osmoreception, which could trigger functional differentiation of chloride cells.

Adaptation, Physiological↗

PubMed2006

A composition-based cartilage model for the assessment of compositional changes during cartilage damage and adaptation.

OBJECTIVE: The composition of articular cartilage changes with progression of osteoarthritis. Since compositional changes are associated with changes in the mechanical properties of the tissue, they are relevant for understanding how mechanical loading induces progression. The objective of this study is to present a computational model of articular cartilage which enables to study the interaction between composition and mechanics. METHODS: Our previously developed fibril-reinforced poroviscoelastic swelling model for articular cartilage was combined with our tissue composition-based model. In the combined model both the depth- and strain-dependencies of the permeability are governed by tissue composition. All local mechanical properties in the combined model are directly related to the local composition of the tissue, i.e., to the local amounts of proteoglycans and collagens and to tissue anisotropy. RESULTS: Solely based on the composition of the cartilage, we were able to predict the equilibrium and transient response of articular cartilage during confined compression, unconfined compression, indentation and two different 1D-swelling tests, simultaneously. CONCLUSION: Since both the static and the time-dependent mechanical properties have now become fully dependent on tissue composition, the model allows assessing the mechanical consequences of compositional changes seen during osteoarthritis without further assumptions. This is a major step forward in quantitative evaluations of osteoarthritis progression.

Adaptation, Physiological↗

PubMedDate not supplied

[Cyclosporin A inhibits the response of osmotic water permeability to antidiuretic hormone in toad's bladder and to angiotensin II and antidiuretic hormone in toad's skin].

The purpose of the present study was to assess the effects of cyclosporine A (CyA) in the osmotic water flow response of isolated toad bladder to arginine-vasotocin (AVT) and to angiotensin II (Ang II) and AVT in isolated toad skin. CyA added to the dermal side of isolated toad skin or to the serosal side of toad bladder in concentrations of 0.42. 10(-6) M to 0.42. 10(-7) M had no effect on basal osmotic water permeability (Posm) but inhibited the hormonal response to AVT in both membranes (AVT 10(-10) M in toad bladder and 10(-8) to 10(-9) M in toad skin). CyA also inhibited the Posm response to Ang II (10(-7) M) in toad skin in concentrations of 0.42. 10(-6) M and 0.42. 10(-7) M. In toad bladder it could be demonstrated that the inhibitory effect was reversible. CyA in concentrations of 0.42. 10(-6) M inhibited the Posm response of toad skin to theophylline (3.2. 10(-3) M) and to dibutyryl cyclic AMP (6.3. 10(-3) M) suggesting an effect distal to the generation of cyclic AMP. These responses would support the possibility of a diuretic effect in the mammalian nephron.

Angiotensin II↗

PubMed1991

Coupled water transport by rat proximal tubule.

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to examine water reabsorption by this epithelium. Osmolality of the luminal solution was varied with changes in NaCl concentration and by the addition of raffinose. Capillary perfusates contained either low (2 g/dl) or high (16 g/dl) concentrations of albumin. We used low-bicarbonate perfusates for both lumen and capillary so that we might apply the nonequilibrium thermodynamic model of transport for a single solute (NaCl) to interpret our observations. Linear regression with the volume flux equation Jv = -Lp delta II - Lp sigma delta C + Jav (where Jv is volume flux, Lp is hydraulic conductance, delta II is oncotic force, sigma is osmotic reflection coefficient, delta C is salt concentration difference, and Jav is the component of Jv not attributed to transepithelial hydrostatic or osmotic forces) revealed a tubule water permeability (Pf = 0.11 +/- 0.01 cm/s) and a sigma (0.74 +/- 0.08) in agreement with previous determinations. These transport parameters were unaffected by changes in peritubular protein. We also found that Jav was substantial, approximately three-fourths of the rate of isotonic transport under these perfusion conditions. Further, this component of water transport nearly doubled with the transition from low- to high-protein peritubular capillary perfusion. When expressed as a capacity for water reabsorption against an osmotic gradient, the salt concentration differences required to null volume flux were 13.2 +/- 2.4 and 29.4 +/- 4.0 mosmol/kgH2O under low and high peritubular protein. Our data suggest that this protein effect is, most likely, an increase in solute transport by the tubule epithelial cells.

Absorption↗

PubMed1998

Intestinal water absorption--implications for the formulation of rehydration solutions.

Absorption of ingested water and most solutes occurs in the proximal small intestine, therefore the rate at which beverages are emptied from the stomach is an important factor in determining the rate of water absorption. In the small intestine, water absorption is brought about by the creation of suitable osmotic gradients that promote net uptake of water from the intestinal lumen. The absorption of solute, especially that brought about by active carriers, are highly effective in creating the osmotic gradients that promote net water uptake. The activation of these transporters also increases the permeability of the mucosa which helps absorption. Moderate hypotonicity of the luminal contents potentiates solute-induced water absorption while hypertonicity slows fluid absorption. Dilute hypotonic glucose-sodium solutions are highly effective oral rehydration solutions, and the type of carbohydrate used does not appear to be important. The addition of other actively absorbed solutes gives little benefit in potentiating water uptake. The inclusion of sodium in rehydration solutions may not be required to stimulate water absorption but probably assists the overall rehydration process. The amount of glucose required to stimulate water absorption is relatively small and for rehydration purposes ingestion of an adequate amount of a dilute solution is more beneficial than drinking a smaller volume of a more concentrated beverage.

Biological Transport↗

PubMed1989

Trypsin affects basal and stimulated osmotic water permeability in isolated toad skin.

1. We investigated the effect of trypsin (Tryp) on basal, stimulated and fluphenazine (FPZ)-inhibited net water flow (Jw) through isolated toad skin (Bufo arenarum). 2. Epidermal Tryp (20 min) promoted an increase in basal Jw which was dose-dependent (maximal with 0.5 mg/ml) and was prevented by a Tryp inhibitor (SBTI). 3. Tryp treatment inhibited the subsequent response to substances known to act before (oxytocin, Oxy) or after cyclic AMP (cAMP) generation (theophylline). 4. Tryp-induced Jw was not additive with the maximal response to Oxy or theophylline and did not modify FPZ's inhibitory effect on stimulated Jw. 5. Dermal Tryp (0.5 mg/ml, 20 min) did not modify basal, but inhibited Oxy and isoproterenol-stimulated Jw, without altering the response to theophylline or db-cAMP. 6. Collectively, our results show a differential action for epidermal and dermal Tryp. Tryp's side-selective action enables its use as a pharmacological tool in the functional dissection of Jw across toad skin.

Animals↗