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PubMed1987

Water permeability and particle aggregates in ADH-, cAMP-, and forskolin-treated toad bladder.

Osmotic water flow was used to evaluate total tissue water permeability (Ptissue), and luminal membrane particle aggregates, presumed sites for transmembrane water movement, were quantified to assess luminal membrane water permeability, in bladders treated with maximally stimulating concentrations of antidiuretic hormone (ADH), adenosine 3',5'-cyclic monophosphate (cAMP), and forskolin. Aggregates were as numerous and occupied the same fractional area of the luminal membrane in response to cAMP treatment (10 mM) as treatment with ADH (20 mU/ml). Ptissue in cAMP-treated tissues, however, was only half of that induced by ADH (P less than 0.001). A similar disparity in the relationship between aggregates and Ptissue occurred for additional bladders treated with 50 microM forskolin, which is known to increase endogenous cAMP to levels much greater than caused by maximally stimulating concentrations of ADH. Although Ptissue achieved with forskolin was the same in paired bladders treated with ADH, aggregates were far more numerous (P less than 0.05) and occupied much more membrane area (P less than 0.05) with forskolin. These observations are consistent with the view that aggregate appearance in the luminal membrane is a function of intracellular cAMP. The finding that the hydrosmotic response of toad bladder to both cAMP and forskolin compared with ADH stimulation is reduced relative to measured changes in luminal membrane aggregates suggests that the effect of ADH in altering water permeability involves additional regulation via a non-cAMP-mediated mechanism. This latter event would appear to be by an effect of ADH on the permeability of a resistance at a postluminal membrane site and/or possibly on the permeability of aggregates in the luminal membrane.

Animals↗
PubMed1999

Functional analysis of aquaporin-2 mutants associated with nephrogenic diabetes insipidus by yeast expression.

Mutations of aquaporin-2 (AQP2) vasopressin water channel cause nephrogenic diabetes insipidus (NDI). It has been suggested that impaired routing of AQP2 mutants to the plasma membrane causes the disease; however, no determinations have been made of mutation-induced alterations of AQP2 channel water permeability. To address this issue, a series of AQP2 mutants were expressed in yeast, and the osmotic water permeability (P(f)) of the isolated vesicles was measured. Wild-type and mutant AQP2 were expressed equally well in vesicles. P(f) of the vesicles containing wild-type AQP2 was 22 times greater than that of the control, which was sensitive to mercury and weakly dependent on the temperature. P(f) measurements and mercury inhibition examinations suggested that mutants L22V and P262L are fully functional, whereas mutants N68S, R187C, and S216P are partially functional. In contrast, mutants N123D, T125M, T126M, A147T, and C181W had very low water permeability. Our results suggest that the structure between the third and fifth hydrophilic loops is critical for the functional integrity of the AQP2 water channel and that disruption of AQP2 water permeability by mutations may cause NDI.

Animals↗
PubMed1973

Concentrating engines and the kidney. I. Central core model of the renal medulla.

Mass balance relations, valid for any counterflow system, are derived and applied to a central core model of the renal medulla, in which descending Henle's limbs (DHL), ascending Henle's limbs (AHL), and collecting ducts (CD) exchange with a central vascular core (VC) formed by vasa recta loops, assumed so highly permeable that the core functions as a single tube open at the cortical end, closed at the papillary. Solute supplied to the VC primarily by the water impermeable AHL may either enter the DHL to be recycled or remain in the core to extract water by osmosis from DHL and CD. If concentrations in core and descending flows are nearly equal, then for all degrees of recycling the ratio of entering DHL concentration to loop concentration is given by r = 1/[1 - f(T)(1 - f(U))], where f(T) is the fractional net solute transport out of AHL and f(U) is the ratio of CD flow to the sum of CD and AHL flows. Differential equations for a single solute are derived for core and AHL concentrations. Explicit analytic solutions are given for solute transport out of the AHL governed by Michaelis-Menten kinetics. Finally the energy requirements for concentration are analyzed.

Biological Transport↗
PubMed2001

Algae permeability to Me(2)SO from -3 to 23 degrees C.

Biphasic transport of water and dimethyl sulfoxide (Me(2)SO), a common cryoprotective agent (CPA), in algal cells was induced and measured on a cryoperfusion stage. A two-step experimental protocol provided data for the volumetric response of Chlorococcum (C.) texanum to impermeable and permeable solutes. First, the cells were exposed to a 500-mOsm sucrose solution, causing immediate shrinkage of the cell to a minimum equilibrium volume. Then an isoosmotic 200-mOsm/300-mOsm CPA/sucrose solution was introduced to the cells, resulting in increased cell volume to a new equilibrium state. Experiments were conducted at temperatures between -3 and 23 degrees C. Cell volumes were measured off-line by computer analysis of video images. A network thermodynamic model was fit to the transient volume data to determine permeabilities of C. texanum to water and Me(2)SO over the full temperature range, and results were calculated with two numeric methods. Biphasic transport was found to be slower at colder temperatures, with water entering the cell faster than Me(2)SO. Experimental results were also compared with data from similar experiments using methanol (MeOH) as the CPA. MeOH influx was calculated to be a magnitude larger than that of water. Additionally, MeOH permeability was at least three orders of magnitude greater than Me(2)SO permeability, and the difference in these solute permeabilities increased as temperature decreased.

Biological Transport, Active↗
PubMed1992

cAMP-dependent protein kinase mediates hydrosmotic effect of vasopressin in collecting duct.

The role of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) in mediating the hydrosmotic effect of vasopressin in in vitro microperfused rabbit cortical collecting ducts (CCDs) was examined. We measured PKA substrate phosphorylation and water permeability [hydraulic conductivity (Lp) = 10(-7) cm.atm-1.s-1], stimulated by substituted cAMP analogues selective for a unique cAMP binding site (site A or B) on PKA regulatory subunit (R). Synergy between site A- and site B-selective analogues suggests involvement of PKA, because both sites must be occupied for R to dissociate from the catalytic subunit (C), allowing phosphorylation to proceed. As single agents, the site B-selective analogues 8-(4-chlorophenylthio)-cAMP (8-CPT) and 8-thiomethyl-cAMP (8-SCH3) were at least two orders of magnitude more potent than the site A-selective analogues N6-monobutyryl-cAMP (N6-mono) or N6-benzoyl-cAMP (N6-benz). Combinations of subthreshold concentrations of two site A analogues (N6-mono+N6-benz) or two site B-selective analogues (8-CPT + 8-SCH3) failed to significantly increase protein phosphorylation or water permeability. In contrast, combination of a site A plus site B analogue synergistically stimulated both protein phosphorylation and Lp. Rp-cAMPS, an inhibitor of cAMP binding to PKA, reduced both vasopressin (41% inhibition)- and cAMP (56% inhibition)-stimulated water permeability. H-89 (50 microM), an inhibitor of PKA kinase activity, also blocked cAMP-stimulated water permeability (90% inhibition). These findings suggest that vasopressin-induced water permeability in the rabbit CCD is mediated by PKA.

Animals↗
PubMed1976

Selective inhibition of osmotic water flow by general anesthetics to toad urinary bladder.

Vasopressin increases the permeability of the total urinary bladder, an analogue of the mammalian renal collecting duct, to water and small solutes, especially the amide urea. We have observed that three general anesthetic agents of clinical importance, the gases methoxyflurane and halothane and the ultrashortacting barbiturate methohexital, reversibly inhibit vasopressin-stimulated water flow, but do not depress permeability to urea, or the the lipophilic solute diphenylhydantoin. In contrast to their effects in vasopressin-treated bladders, the anesthetics do not inhibit cyclic AMP-stimulated water flow, consistent with an effect on vasopressin-responsive adenylate cyclase. The selectivity of the anesthetic-induced depression of water flow suggests that separate adenylate cyclases and cyclic AMP pools may exist for control of water and urea permeabilities in to toad bladder. Furthermore, theophylline's usual stimulatory effect on water flow, but not its effect on urea permeability, was entirely abolished in methoxyflurane-treated bladders, suggesting that separate phosphodiesterases that control water and urea permeabilities are present as well. We conclude that the majority of water and urea transport takes place via separate pathways across the rate-limiting luminal membrane of the bladder cell, and that separate vasopressin-responsive cellular pools of cyclic AMP appear to control permeability to water and to urea.

Anesthetics↗
PubMedDate not supplied

[Comparative evaluation of cuprophane and cellophane used as membranes for hemodialysis].

Investigations into the structure, mechanical properties and permeability of the Soviet-made cellophane, cellulose film No 100 and cuprophane have shown the Soviet-made cellophane membrane to be inferior to cuprophane with regard to the strength and permeability of low-molecular metabolites. High strength properties of the cellulose film No 100 go with a much more lower permeability than in the case of cuprophane and cellophane. Sterilization with gamma-irradiation does not have any material effect on the physico-mechanical and functional characteristics of the membranes. Ways and means for improving the strength and permeability of the hydrate-cellulose membranes are outlined.

Cellophane↗
PubMed2001

[A pressure gravity-diffusive effect for flat polymeric membrane and ternary non-electrolyte solutions].

In this paper the pressure gravidiffusive model equation in a single-membrane osmotic-diffusive cell is elaborated. In this cell the flat, microporous and symmetric polymeric membrane so-called Nephrophane positioned horizontally separated water and binary (aqueous glucose or aqueous ethanol) or ternary (glucose in 0.2 mol.l-1 aqueous ethanol or ethanol in 0.05 mol.l-1 aqueous glucose) non-electrolyte solutions. The calculations of pressure gravidiffusive effects for the configurations A and B of the single-membrane osmotic-diffusive cell were elaborated. In configuration A solution was placed in compartment below membrane and in configuration B--above membrane. The calculated result are interpreted in terms of the convective instability that increases the diffusive permeability coefficient of complex: concentration boundary layer/membrane/concentration boundary layer.

Cell Membrane↗
PubMed2004

Theoretical prediction of 'optimal' freezing programmes.

We have developed a quantitative description of the osmotic behaviour of cells during freezing without a presupposed value of the cooling rate. Instead, at all times the intracellular supercooling is maximised provided that it does not exceed a predetermined value 'p' (e.g., 2 degrees C). This should preclude intracellular ice formation, but also ensures that the osmotic gradient and the CPA concentration gradient are limited, as well as the gradient driven transmembrane fluxes of water and CPA. Using the condition of a constant level of supercooling of p degrees C, equations can be derived to generate non-linear cooling curves in which at all times the cooling rate is maximised (to minimise slow cooling damage), while preventing conditions that could lead to fast cooling damage. Simulations of the osmotic events during freezing, and prediction of the 'optimal' freezing curve can be performed provided that values are available for the membrane permeability coefficients for water (L(p)) and cryoprotectant (P(s)), and their respective activation energies, the initial intracellular osmotically active aqueous volume, and the membrane surface area. Simulations are shown, both with and without permeant solute, to demonstrate how the predicted 'optimal' freezing curve is affected by medium composition, and by membrane permeability and osmotic cell characteristics.

Animals↗
PubMed1986

Diluting segment in avian kidney. II. Water and chloride transport.

The mammalian-type nephrons of avian kidneys contain a Henle's loop that runs parallel to the collecting ducts and the vasa recta. Thus we examined whether the thick ascending limb (TAL) of Henle's loop of the avian kidney acts as a diluting segment by measuring water and Cl transport in the isolated and perfused TAL of the quail, Coturnix coturnix. The TAL showed a lumen-positive transepithelial voltage (Vt) (+9.4 +/- 0.4 mV, n = 28). Net water flux (Jv) was nearly zero when the TAL was perfused and bathed with isosmotic solution. When the osmotic gradient was imposed, Jv increased only slightly, and thus the osmotic water permeability (Lp) was low. Arginine vasotocin (AVT) added to the hyperosmotic bath did not alter either Jv, Lp, or Vt. Cl efflux (lumen to bath, 370.4 +/- 27.7 peq X mm-1 X min-1) was higher than Cl influx (bath to lumen, 98.6 +/- 14.3 peq X mm-1 X min-1) when measured in the different tubules. AVT showed no effect on Cl efflux. These results indicate that in the TAL of the quail osmotic water permeability is low while net Cl reabsorption is present, suggesting that the TAL functions as a diluting segment.

Animals↗
PubMed1964

ROLE OF EDTA AND METALS IN MITOCHONDRIAL CONTRACTION.

STUDIES COMPARING THE STATE OF HYDRATION AND DEHYDRATION OF RAT LIVER MITOCHONDRIA TO THEIR CONTENT OF ATP, CA, AND FATTY ACID, ALONG WITH THE RATE OF ATP HYDROLYSIS, AS WELL AS MICROSCOPIC APPEARANCE OF MITOCHONDRIA, HAVE LED TO THE FOLLOWING GENERALIZATIONS: 1. The competition between cationic translocations and water translocation for the available chemical energy (ATP) determines under many circumstances the water content of mitochondria. 2. Swelling of mitochondria by electron transport substrates is an example of the activation of the cationic translocations at the expense of water translocation. 3. Electron micrographic studies are interpreted to indicate that EDTA alone can cause condensation and dehydration of the mitochondrial matrix. However, both EDTA and substrate are necessary to remove appreciable quantities of water from mitochondrial intramembranous spaces. 4. Since the data in the accompanying report indicated that EDTA, in the absence of energy, decreased the permeability of mitochondrial membranes, it appears likely that ballooning of intramembranous spaces, following addition of EDTA, represents trapping of water between two semipermeable membranes following dehydration of mitochondrial matrix.

Adenosine Triphosphatases↗
PubMed1982

Extracellular Ca2+ and the effect of antidiuretic hormone on the water permeability of the toad urinary bladder: an example of flow-induced alteration of flow.

The extracellular Ca2+ requirement for antidiuretic hormone (ADH) stimulation of water permeability in the toad urinary bladder has been critically examine. The polarity of the tissue was maintained with 1 mM Ca2+ in the mucosal bathing medium and a serosal bath nominally free of Ca2+. Under these conditions, ADH-induced osmotic water flow was inhibited by more than 60% while enhancement of the diffusional permeability to water was unaffected. Structural studies revealed that low serosal Ca2+ led to parallel alterations in epithelial architecture that amounted to a significant distortion of the osmotic water pathway. Prevention of these alterations, or restoration of normal cell-cell contact showed that the reduction of serosal Ca2+ did not restrict hormonal action per se, but that it resulted in a weakening of cell-cell junctions such that intercellular space distension during water flow occurred to a point where the geometric conditions for maintenance of osmotic flow were compromised. We conclude that extracellular Ca2+ is not a requirement for the molecular aspects of ADH action but that, in its absence, a direct measurement of ADH-induced osmotic flow proves to be an inaccurate index of the hormone-generated changes in epithelial transport characteristics. Under certain conditions the ADH-effect on the tissue's hydraulic permeability is probably best assessed by measurement of the diffusional permeability to water; although accuracy in this determination is difficult, it is not as strongly dependent on tissue geometry.

Animals↗
PubMed2001

Molecular mechanisms of water and solute transport across archaebacterial lipid membranes.

Archaebacteria thrive in environments characterized by anaeobiosis, saturated salt, and both high and low extremes of temperature and pH. The bulk of their membrane lipids are polar, characterized by the archaeal structural features typified by ether linkage of the glycerol backbone to isoprenoid chains of constant length, often fully saturated, and with sn-2,3 stereochemistry opposite that of glycerolipids of Bacteria and Eukarya. Also unique to these bacteria are macrocyclic archaeol and membrane spanning caldarchaeol lipids that are found in some extreme thermophiles and methanogens. To define the barrier function of archaebacterial membranes and to examine the effects of these unique structural features on permeabilities, we investigated the water, solute (urea and glycerol), proton, and ammonia permeability of liposomes formed by these lipids. Both the macrocyclic archaeol and caldarchaeol lipids reduced the water, ammonia, urea, and glycerol permeability of liposomes significantly (6-120-fold) compared with diphytanylphosphatidylcholine liposomes. The presence of the ether bond and phytanyl chains did not significantly affect these permeabilities. However, the apparent proton permeability was reduced 3-fold by the presence of an ether bond. The presence of macrocyclic archaeol and caldarchaeol structures further reduced apparent proton permeabilities by 10-17-fold. These results indicate that the limiting mobility of the midplane hydrocarbon region of the membranes formed by macrocyclic archaeol and caldarchaeol lipids play a significant role in reducing the permeability properties of the lipid membrane. In addition, it appears that substituting ether for ester bonds presents an additional barrier to proton flux.

Archaea↗
PubMed2001

[Increase of water permeability and recovery of water impermeability of the frog urinary bladder].

The experiments carried out on the urinary bladder of the frog Rana temporaria L. have shown that the period of recovery of water impermeability after an increase of osmotic water permeability induced by arginine-vasotocin, desmopressin, or cAMP depends on the degree of increase of the osmotic permeability but not on the nature of the substance stimulating the increase of osmotic water permeability. The removal of the hormone in the absence of autacoids fails to recover the water impermeability. After cessation of the vasotocin action the water permeability decrease is delayed if phospholipase A2 and cyclooxygenase are inhibited by qiunacrine and voltaren, respectively. An agonist of V1-receptors has no effect on dynamics of the recovery of water impermeability. This recovery has been shown to depend on PGE2 concentration in the serosal solution after the hormone removal. The obtained results indicate that decrease of water permeability depends not only on removal of vasotocin or cAMP but also on involvement of autacoids.

Animals↗
PubMed1982

Osmotic permeabilities across corneal endothelium and antidiuretic hormone-stimulated toad urinary bladder structures.

Osmotic permeabilities of several epithelial structures have been determined with novel optical procedures based on specular microscopy. The osmotic permeabilities of several tissue layers were determined by continuously monitoring the position of the apical tissue borders while an osmotic flow was imposed across those layers. The values found were (in micrometer/s; mean +/- SE): corneal epithelium, 137 +/- 30 (n = 5): antidiuretic hormone stimulated toad bladder, 429 +/- 64 (n = 6); and corneal endothelium, 711 +/- 34 (n = 7). In addition, the osmotically-induced transient change in thickness of the corneal endothelial cells was determined with the help of a computer, and the apparent osmotic permeability measured for the apical membrane was 1420 +/- 160 micrometer/s (n = 5). It is concluded that the osmotic permeability across the endothelial layer is sizably larger than had been previously detected and that osmotic flows across such layer largely traverse the cellular membranes. With osmotic permeability values (per unit of cell membrane area) as large as presently reported, isotonic fluid transport by epithelia can be explained simply on the basis of local osmotic gradients.

Animals↗
PubMed1980

Effect of osmotic gradient on ADH-induced intramembranous particle aggregates in toad bladder.

Paired toad urinary bladders were prepared without or with an osmotic gradient (175 mosM) across them, stimulated for 2.5 (n = 6), 5 (n = 6), 30 (n = 6) or 60 (n = 6) min with ADH (20 mU/ml), and studied by freeze-fracture electron microscopy. Water permeability at these times was assessed in additional bladders (n = 6 for each case) after tissue fixation according to the technique of Eggena. After both 60 and 30 min of ADH stimulation, the presence of a gradient compared with the absence of one was associated with fewer aggregates (242 +/- 35 vs. 382 +/- 14 x 235 micron-2 at 60 min, P less than 0.01; 279 +/- 36 vs. 470 +/- 51 x 235 micron-2 at 30 min, P less than 0.01) and lower water permeability (8.4 +/- 1.1 vs. 18.8 +/- 1.8 microgram x min-1 x cm-1 x mosM-1 at 60 min, P less than 0.005; 9.2 +/- 1.0 vs. 22.0 +/- 2.1 microgram x min-1 x cm-2 x mosM-1 at 30 min, P less than 0.001). In addition, with a gradient both maximum water permeability and maximum aggregate frequency were reached nearly together; a similar correspondence occurred without a gradient. We conclude that in the presence of an osmotic gradient both the ADH-associated aggregates and the water permeability response to ADH are prevented from reaching the higher levels observed in bladders not exposed to a gradient.

Animals↗