Water pathways across a reconstituted epithelial barrier formed by Caco-2 cells: effects of medium hypertonicity

Caco-2 cells, originated in a human colonic cancer, are currently used as model systems to study transepithelial transports. To further characterize their water permeability properties, clone P1 Caco-2 cells were cultured on permeable supports. At confluence, the transepithelial net water movement (Jw), mannitol permeability (Ps), and electrical resistance (R) were simultaneously measured. The observed results were correlated with transmission and freeze-fracture electron microscopy studies and compared with those obtained, in similar experimental conditions, in a typical mammalian epithelial barrier: the rabbit rectum. When the serosal solution was made hypertonic (50 mM polyethylene glycol-PEG), the spontaneously observed secretory Jw rapidly reversed, became absorptive and then stabilized. Simultaneously, the R values dropped and Ps went up. In the case of the rabbit rectal epithelium, a similar treatment did not elicit significant changes in the water permeability during the first 20 min following the osmotic challenge while there was a significant increase in the transepithelial resistance. After exposure to serosal hypertonicity, several morphological modifications developed in the Caco-2 cells: Localized dilations in the intercellular spaces and vacuoles in the cytoplasm appeared. Nevertheless, most cells remained in contact and no evidence of cell shrinking was observed. Simultaneously, the tight-junction structure was more or less disorganized. The filament network lost its sharpness and "omega" figures appeared, bordering the intercellular spaces. In some cases the tight-junction network was completely disrupted. In the case of the rabbit rectum the structural modifications were completely different: Serosal hypertonicity rapidly induced cell shrinking and the opening of the intercellular spaces, with no noticeable change in the tight-junction structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Aquaporin-CHIP-related protein in frog urinary bladder: localization by confocal microscopy

Aquaporin CHIP, a 28 kDa channel forming protein, has been proposed to function as water channel in both erythrocyte and kidney proximal tubule. Recently, we have reported that in frog urinary bladder, a model of the kidney collecting tubule, polyclonal antibodies against human erythrocyte CHIP recognize and immunoprecipitate a 30 kDa protein from the epithelial cell homogenate. In the present work confocal fluorescence microscopy was used to determine the cellular and subcellular localization of CHIP28-like proteins in the urinary epithelium. A clear labeling of the apical border was found after Triton X-100 permeabilization. The labeling was distributed throughout the apical domain and not restricted to specific domains of the membrane. The staining was also present in the deeper confocal sections where the fluorescence seems to be localized at the cellular contour. No difference in the labeling patterns was observed between resting and ADH-treated bladder. Specificity of the staining was confirmed by the absence of the labeling pattern when antiserum was preadsorbed on CHIP28 protein immobilized on Immobilon P stripes. Our results suggest that CHIP-like proteins are not proteins inserted in the apical membrane during the antidiuretic response. Moreover, we do not know whether the labeling was due to the presence of CHIP28 itself or an as-yet-unidentified protein sharing immunological analogies with aquaporin CHIP.

Activation of the vasopressin-sensitive water permeability pathway in the toad bladder by N-ethyl maleimide

Vasopressin stimulates transepithelial water flow in the toad urinary bladder. We report here that N-ethyl maleimide (NEM) (0.1 mM) produces a similar increase in osmotic water flow when applied to the mucosal surface of the tissue. NEM-induced water flow is sensitive to inhibitors of hormone-induced water flow, including serosal acidification, or exposure to quinidine or cytoskeleton-disruptive drugs. NEM-induced water flow is additive with that induced by a submaximal, but not a maximal, dose of vasopressin. The response to mucosal NEM is not reversed on removal of the reagent, but established NEM-induced water flow can be inhibited by serosal acidification or quinidine. Like vasopressin, mucosal NEM induces the appearance of fusion profiles and intramembranous particle aggregates (putative water channels) in the apical plasma membrane of the granular cells, and the incidence of particle aggregates correlates with water flow. NEM does not cause an increase in intracellular cAMP. Our data suggest that NEM stimulates transepithelial water flow by irreversibly activating cellular mechanisms normally triggered by vasopressin, hence causing the insertion of water channels.

Antidiuretic response in the urinary bladder of Xenopus laevis: presence of typical aggrephores and apical aggregates

The urinary bladder of the aquatic toad Xenopus laevis is known to exhibit a low permeability to water and a poor sensitivity to antidiuretic hormone. In order to precise the characteristics and the specific cellular mechanisms of this reduced hydro-osmotic response we used a sensitive volumetric technique to monitor net water flow and studied the correlation between the antidiuretic hormone (ADH)-induced net water flow and the fine ultrastructural appearance of the urinary bladder epithelium. Transmural net water flow was entirely dependent on the osmotic gradient across the preparation and not on the hydrostatic pressure difference. We observed the existence of a low but significant hydro-osmotic response to arginine vasopressin. Freeze-fracture electron microscopy demonstrated the presence of typical aggrephores in the subapical cytoplasm. The response to the hormone was accompanied by the appearance of typical intramembrane aggregates into the apical plasma membrane. Water permeability increase and apical aggregate insertion were both slowly but fully reversible. Except for the multilayered structure of the epithelium and the particularly low response to antidiuretic hormone, all the studied permeability and ultrastructural characteristics of the bladder were thus very similar to those observed in other sensitive epithelia such as the amphibian bladder and skin and the mammalian collecting duct which exhibit a high hydro-osmotic response to the hormone.

Water handling in Caco-2 cells: effects of acidification of the medium

Caco-2 cells were cultured on permeable supports. At confluence the minute-by-minute net water movement (Jw) was automatically recorded. Simultaneously, unidirectional [14C]mannitol, 22Na+, and/or 36Cl- fluxes and transepithelial resistances were measured. The water and mannitol permeabilities went progressively down between 9 and 16 days after seeding and then stabilized. In this last condition the hydrostatic permeability coefficient (Phydr) was 2.67 +/- 0.31 cm s-1 while the osmotic permeability coefficient (Posm) was 0.0017 +/- 0.0004 cm s-1. Phydr but not Posm was dependent on the temperature and on the presence of Na+ in the medium. A net secretory Jw was observed 16 days after seeding, in the absence of any osmotic, hydrostatic or chemical gradient. This secretory Jw was associated with net Cl- (1.43 +/- 0.43 muequiv h-1 cm-2) and Na+ (1.05 +/- 0.35 muequiv h-1 cm-2) secretions. Amiloride reduced, in open-circuit conditions, both Na+ and Cl- apical to basal fluxes, thus enhancing the net Na+ and Cl- exit. Acidification of the medium (pH 6.2) reversibly increased water and mannitol permeabilities in 10-day-old cultures. In 16-day-old cultures the same shift in medium pH did not change mannitol permeability, while stimulating water secretion. These results, obtained in the absence of supracellular structures (villae, crypts) and subepithelial components (muscular, vascular and conjunctive tissues) indicate that paracellular and transport-associated water pathways are sensitive to changes in the pH of the medium in Caco-2 cell layers.

Effects of salt acclimation on water and urea permeabilities across the frog bladder: Relationship with intramembrane particle aggregates

1. In salt-acclimated frogs, water and urea bladder permeabilities are markedly higher than in tap water-acclimated animals. 2. Intra-membrane particle aggregates (IMPA) cover an unusually large surface area of the salt-acclimated frog bladder apical plasma membrane. 3. In saline-adapted animals, proteins extracted from the apical plasma membrane contain additional species of 19, 26, 31 and 53-61 kDa. These proteins might be related to the water channels contained by IMPA.

Selected polyclonal antibodies and ADH challenge in frog urinary bladder: a label-fracture study

It is clearly established that the changes induced by antidiuretic hormone (ADH) in its target epithelial cells result from the insertion in the apical membrane of new components that contain channels for water. We have already undertaken an initial study of these channels by raising polyclonal antibodies against Triton X-100 apical extracts from ADH-treated bladders and approached their purification by different adsorption steps. In the present study, we used the label-fracture technique to investigate the localization of the binding sites of the obtained polyclonal antibodies on the apical membrane of ADH-stimulated frog urinary bladder. The results obtained clearly demonstrated a preferential labeling by the selected antibodies of morphological structures such as the groove arrays and the fusion images that are generally accepted as being involved in ADH-induced changes in water permeability of the apical membrane.

Vesicles and particles of sodium bis(2-ethylhexyl) phosphate in binary and ternary systems

Vesicles were identified in aqueous solution of pure sodium bis(2-ethylhexyl) phosphate, a short branched chain surfactant. Superficial tension measurements show that the vesicles appear above a molality of 0.02 (0.69 %w). These aggregates are equilibrium structures. The "packing parameter' theory established by Israelachvili et al. allows the prediction of the occurrence of such vesicles. If an organic solvent, such as xylene or ethylhexanoate, is added to the binary system, a different type of aggregate appears, the size of which is determined by several methods including electron microscopy and light scattering. Interfacial tension measurements show that these aggregates would be expected to form above a molality of 0.02. According to our experimental results, the microstructure of these aggregates can be described as micelles and/or vesicles, swollen or not.

ADH-induced water permeability and particle aggregates: alteration by a synthetic estrogen

In the amphibian urinary bladder, the increase in water permeability induced by antidiuretic hormone (ADH) is accompanied by the appearance of apical intramembrane particle (IMP) aggregates that are believed to contain specific channels for water. In a previous work, we have shown that 3,3'-diallyldiethylstilbestrol (DADES), a synthetic estrogen which is a blocker of the glucose transporter, also inhibits the hydrosmotic response to ADH in the bladder. Our aim in the present study was to analyze the alterations of the membrane fine structure further and to correlate them with the water permeability changes. The results point to a selective inhibition of the ADH-induced net water flow, probably due to an interference with one of the last steps of the response to the hormone. This inhibition is associated with an increase in the density of the apical IMP aggregates, which are thus probably not operational. The resting net water flow is not inhibited and, surprisingly, typical IMP aggregates are frequently observed in the apical membrane after DADES treatment. The compound also induces the appearance of unusual loose IMP clusters that can only be seen on the apical membrane of the granular cells and that share several ultrastructural similarities with the ADH-induced aggregates. These results suggest that 1) apical DADES treatment stimulates the insertion of IMP aggregates in the apical membrane of the urinary bladder and 2) DADES inhibits the ADH-induced water flow by interfering with the aggregates and thus probably by blocking the specific water channels.

Antidiuretic response: what markers for water channel components?

Antidiuretic hormone increases the water permeability of its target epithelial tissues by triggering the insertion into the apical cell membrane of aggregated intramembrane particles that contain channels specific for water. Little is known about the chemical composition of these membrane particles and of the water channel components. Present work describes a procedure for obtaining selected antibodies that specifically recognize ADH-induced components of the apical membrane in the amphibian urinary bladder epithelial cells.

Effects of PCMBS on the water and small solute permeabilities in frog urinary bladder

It has been reported that PCMBS (p-chloromercuribenzene sulfonate) blocks the water permeability of red cells and of the tubular kidney membranes. In this study we compare the effects of this mercurial compound on the permeability of water and other small solutes in the frog urinary bladder. We observed that: (i) 5 mM PCMBS applied at pH 5.0 to the mucosal side inhibited the net and unidirectional water fluxes induced by oxytocin without changing the delta Pf/delta Pd ratio. (ii) The oxytocin-induced urea and Na+ influxes were also inhibited by PCMBS. (iii) The unidirectional Cl- movement was first reduced and then increased during the course of PCMBS treatment. (iv) The short-circuit measured at low mucosal Na+ concentration (10 mM), diminished continuously, whereas the transepithelial resistance first increased and then diminished. (v) Mannitol, raffinose, alpha-methyl-glucose, antipyrine, caffeine and Rb+ movements were not changed significantly during the first 26 min of the water permeability inhibition.

IN CONCLUSION

(i) The ADH-sensitive water, urea and Na+ transport systems were inhibited by PCMBS, (ii) PCMBS did not induce a nonspecific and general effect on the permeability of the membrane during the development of the water permeability inhibition, and (iii) in terms of water channels, the inhibition of water transport with the maintenance of a high Pf/Pd ratio suggests that PCMBS closes the water channels in an all or none manner, reducing their operative number in the apical border of frog bladder.

[Exchanges of medical students from Rennes/Erlangen-Nuremberg: various considerations on these exchanges within the E.E.C. framework]

The current political trends of the European Economic Community (EEC) have made it more desirable than ever before for medical students to be able carry out part of their training in medical schools other than their Faculties of origin. The authors examine successively: 1) The results of 20 years of twinning-between the Medical Schools of Rennes (France) and Nürnberg-Erlangen (W. Germany). A considerable number of syllabuses and examinations are now recognized as equivalent. So far, nearly 500 students have taken advantage of the possibilities of exchanges lasting a few months or even a full University year. 2) The propositions submitted by the Medical Schools of Rennes and Strasbourg have been selected from the 800 presented by EEC Universities as port of the Erasmus programme. For the whole of the EEC, 12 medical projects have been started up since october 1989. Among the other projects accepted were those of Bonn and Hamburg, Ovideo and Valence, Naples and Barri, Dublin, Coïmbra, Brussels, Copenhagen, Leyden, etc. 3) In order to strengthen the North-South axis of the EEC and to widen further the horizons of European medical students (even beyond Europe), the Medical Facilities of Rennes and of Alcalà de Henares (University of Madrid) have just defined syllabus and examination equivalences as Rennes and Erlangen did some twenty years ago.

Effect of mercurial compounds on net water transport and intramembrane particle aggregates in ADH-treated frog urinary bladder

It has been suggested that during the oxytocin-induced hydrosmotic response, water crosses the luminal membrane of urinary bladder epithelium cells through membrane-spanning proteins. Although specific inhibitors of osmotic water transport have not been found, certain sulfhydryl reagents such as mercurial compounds may help to identify the proteins involved in this permeation process. We tested the effects of p-chloromercuribenzene sulfonate (PCMBS) and of fluorescein-mercuric acetate (FMA) on the net water flux, the microtubule and microfilament structures of the frog urinary bladder, and the distribution of intramembrane particle aggregates in the luminal membrane. We observed that: (i) 5 mM PCMBS at pH 5 and 0.5 mM FMA at pH 8 added to the mucosal bath at the maximum of the response to oxytocin partially inhibited the net water flux. Inhibition then increased progressively when the preparation was repeatedly or continuously stimulated, until it reached a maximal inhibition at 120 min. This inhibition was not reversed even when cystein was added in the mucosal bath. PCMBS and FMA effects were also observed when cyclic AMP (3',5' cyclic adenosine monophosphate) was used to increase water permeability, (ii) PCMBS mucosal pretreatment did not modify the basal water flux but potentiated the inhibitory effect of PCMBS or FMA on the hydrosmotic response to oxytocin. (iii) Microtubule and microfilament network, visualized in target cells by immunofluorescence, was not affected by PCMBS. (iv) The maximal PCMBS or FMA inhibition was not associated with a reduction of aggregate surface area in the apical membrane. The persistence of the intramembrane particle aggregates associated with the oxytocin-induced hydrosmotic response during the net water flux inhibition by PCMBS, suggests that the PCMBS effect occurs possibly at the level of sulfhydryl groups of the water channel itself.

To what extent is microtubular network involved in antidiuretic response?

Antimitotic drugs markedly interfere with antidiuretic response, strongly implying that cytoskeleton integrity is essential to this function. This role of the cytoskeleton in controlling the epithelial transport has been seen as a necessary step in the translocation of the water channel containing particle aggregates and in their delivery to the apical membrane. We have now reexamined the exact role of the microtubular network by appropriate time course determinations, by the use of microtubule disruptive agents that lack of the side effects of colchicine, and by trying to visualize the apparent modifications of the microtubular network that accompany water permeability alterations using immunocytochemical techniques. Our results fully confirm that after microtubular network disruption, antidiuretic hormone-induced water permeability variations undergo typical alterations consisting in both a reduction in peak net water flow and a slowing down of its onset. At the same time, the microtubular network disappears in all the epithelial cells. We also show that colchicine-induced inhibition can still be observed in the presence of a prostaglandin synthetase inhibitor and that this inhibition is most likely to occur at a post-adenosine 3',5'-cyclic monophosphate level. These data, as well as results from other series with nocodazole, indicate that the reduction of the net water flow directly results from microtubular network disruption and not from side effects of the disrupting drugs. They also show that the hydrosmotic response is only partially dependent on the microtubular network, which probably has only a guidance role in the translocation of particle aggregates and their exocytotic fusion to the apical membrane.

Role of vesicular transport in ADH-stimulated aggregate delivery

It has been assumed from studies in toad bladder that antidiuretic hormone (ADH)-stimulated particle delivery to the luminal membrane is mediated by particle-carrying tubular structures (aggrephores). We report studies in frog and toad urinary bladder showing that vesicles, rather than aggrephores, appear to play the major role in particle delivery in the frog and that vesicle and aggrephore delivery proceed in parallel in the toad. Our principal evidence for this view is that in the frog, transmission electron microscopy shows virtually no fused aggrephores. Supporting evidence includes the following. 1) Freeze-fracture studies show that the diameters of fusion events delivering particles can be quite small, indicating that they are formed by fused vesicles rather than fused aggrephores. 2) A significant population of small fusion events is also seen in the toad, along with larger fusion events related to both aggrephores and large vesicles. 3) Surface aggregate areas in both species are small, consistent with vesicular delivery. 4) Freeze-fracture replicas indicate delivery from shallow pits. We propose a system of transport of particles in which aggrephores act largely as intermediate storage organelles in the frog and as storage and fusion organelles in the toad.

[Propentofylline and its analogs: a new class of agents for in vitro study of the antidiuretic response]

We took profit in this work of the discovery of a novel series of trialkylxanthines, with a biological activity greater than that of the other methylxanthines classically used as cAMP phosphodiesterase inhibitors. First, we determined their hydrosmotic activity, with the hope to find out compounds that could be used as apical agonists. Second, we employed these compounds as tools to further analyze the cellular mechanism of hydrosmotic response. Results show that propentofylline, the most potent compound in this series, exhibits a comparable activity whatever the side of administration, apical or basal. Results further show a similar mode of action in most of the studied conditions. They suggest thus that the same mechanism of action, probably an inhibition of cAMP phosphodiesterase is involved in both apical and basal stimulation. However, they reveal the existence of characteristics that are specific to the apical response. This suggest that an additional mechanism of action is possibly involved in the apically-induced hydrosmotic response.

ADH-induced water permeability: what role for the microtubular network?

1. ADH-induced intramembrane particle aggregates in the apical membrane of the epithelial cells are specifically related to water permeability in the epithelium. 2. Colchicine and nocadozole (both of which bind to tubulin) inhibit ADH-induced osmotic water flow in the amphibian bladder. 3. Microtubules may be involved in the translocation of the aggrephores prior to their insertion into the plasma membrane.

Evidence for a two-site model of forskolin action in frog urinary bladder

In the present study several aspects of the osmotic water-flow-regulation mechanism in frog urinary bladder were examined, utilizing forskolin either as a direct hydrosmotic agent or in association with vasopressin. It was found that forskolin induces a hydrosmotic effect similar to the one induced by vasopressin. This effect is rapid, reversible and dose-dependent. The half-maximally effective concentration (Ec50FSK) is 1.37 microM forskolin. No additional effect on the osmotic water flow was observed when maximal concentrations of forskolin and vasopressin were given simultaneously. Moreover, forskolin can also markedly potentiate vasopressin-induced hydrosmotic response. This potentiation was maximal with submaximal doses of vasopressin, whereas it disappeared when the hormonal concentration was increased to very high levels. Therefore, forskolin increases vasopressin potency without affecting vasopressin efficacy. The Ec50FSK for the forskolin-induced increase in vasopressin potency was 11 nmol, about two orders of magnitude lower than the Ec50FSK for the direct effect of forskolin on the osmotic water transport. On the whole, our results are compatible with a two-site model of forskolin action in frog urinary bladder: a low affinity site (Ec50FSK = 1.37 microM) that mediates the direct action of forskolin on the osmotic water flow and a high affinity site (Ec50FSK = 11 nmol), which mediates the synergic effect of forskolin with the antidiuretic hormone.

Effect of SH-group reagents on net water transport in frog urinary bladder

The basal rate of water reabsorption and its acceleration by oxytocin, cyclic AMP (cAMP) or serosal hypertonicity in frog urinary bladders were monitored before and after exposure of the mucosal surface to sulfhydryl (SH) reactive reagents. The following observations were made: 1. N-ethylmaleimide (NEM, 10(-5)M) did not modify the basal water flux, but did potentiate the hydrosmotic response to oxytocin. At higher NEM concentrations, an increase in the basal flux was observed, while the oxytocin-induced water flux was strongly inhibited, if not, nullified. 2. Iodoacetamide (IAM, 10(-3)M) did not modify the basal water flux but did inhibit the oxytocin-, cAMP-, and serosal hypertonicity-induced increase in water permeability. Furthermore, the time course of the hydrosmotic response to oxytocin was significantly increased. 3. 5,5' dithio-bis-(2-nitrobenzoic acid) (DTNB, 10(-3)M) modified neither the basal nor the oxytocin-induced water flux when incubated at pH 8.1, but potentiated the inhibitory effect of NEM. However, at a mucosal pH of 6.5, DTNB inhibited the response to oxytocin by 30%. These results suggest that: (1) the three SH reagents affect differently the basal and the oxytocin-induced water pathways; and that (2) each of the changes in the oxytocin-induced paths occurs at a step following the hormonally-induced increase in intracellular cAMP concentration.

Glutaraldehyde fixation preserves the permeability properties of the ADH-induced water channels

Unidirectional and net water movements were determined, in frog urinary bladders, before and after glutaraldehyde fixation. Experiments were performed in three experimental conditions: in nonstimulated preparations, after the action of antidiuretic hormone (ADH) and in nonstimulated preparations to which amphotericin B was incorporated from the luminal bath. As previously observed for net water fluxes, the increase in the unidirectional water movement induced by ADH was well preserved by glutaraldehyde fixation. After correction for the effects of unstirred layers and nonosmotic pathways, the observed correlation between the ADH-induced increases in the osmotic (Pf) and diffusional (Pd) permeability coefficients was not modified by the fixative action (before glutaraldehyde: slope 11.19, r: 0.87 +/- 0.07; n = 12; after glutaraldehyde: slope 10.67, r: 0.86 +/- 0.04, n = 39). In the case of amphotericin B, delta Pf/delta Pd = 3.08 (r: 0.83 +/- 0.08), a value similar to that observed in lipid bilayers or in nonfixed toad urinary bladders. It is concluded that: The experimental approach previously employed to study water channels in artificial lipid membranes and in amphibian urinary bladders, can be applied to the glutaraldehyde-fixed frog urinary bladder. Glutaraldehyde fixation does not modify the permeability properties of the ADH-induced water channels. Any contribution of exo-endocytic processes or cell regulatory mechanisms to the observed permeability parameters can probably be excluded. Glutaraldehyde-fixed preparations are a good model to characterize these water pathways.

The role of microtubules and microfilaments in the hydrosmotic response to antidiuretic hormone

To test the effects of colchicine and cytochalasin B on the ADH-induced response, unidirectional and net water fluxes were measured at one or two minutes intervals in frog urinary bladder. The action of these agents on the appearance of intramembrane particles aggregates in the luminal membrane of target cells under oxytocin stimulation and the changes in the tissue ultrastructure induced by cytochalasin B were also studied. It was observed that: the time-course of the response to oxytocin was strongly slowed by colchicine while the washout was not affected; the time-course of the 'on and off' of the response to oxytocin was not modified by cytochalasin B; cytochalasin B pretreatment proportionally reduced unidirectional and net water fluxes measured after glutaraldehyde fixation; the combined action of colchicine and cytochalasin B proportionally reduced the net water flux and the number of intramembrane particles aggregates, observed in freeze-fracture studies; after cytochalasin B action the dilation of intercellular spaces classically observed under oxytocin stimulation is strongly reduced. It is concluded that: microtubules probably play an important role in the water channels plug-in, but not in their removal; microfilaments integrity is necessary for the mechanisms inducing intercellular space dilation and the observed results confirm that water permeability is controlled by the number of permeation units present in the luminal border of granular cells and probably represented by the intramembrane particle aggregates.

Fusion images and intramembrane particle aggregates during the action of antidiuretic hormone. A rapid-freeze study

Antidiuretic hormone (ADH) causes the appearance of water-conducting particle aggregates in the luminal membrane of receptor cells in amphibian bladder and skin, and in the mammalian collecting duct. The aggregates originate from cytoplasmic tubules that fuse with the luminal membrane during ADH stimulation. We have studied the process of fusion and the structure of the particle aggregates by a rapid-freeze technique that renders chemical fixation and glycerol protection unnecessary. Our findings differ in some important respects from previously published work. Aggregate particles, in our study, partition equally between the external (EF) and protoplasmic (PF) membrane leaflets, rather than remaining in the protoplasmic leaflet exclusively. By including the entire population of fusion images in our survey, we have found that aggregate delivery in ADH-treated cells proceeds preferentially from small fusion images whose diameter is significantly less than the 0.12 micron characteristic of the carrier tubules themselves. We have also found that, even in unstimulated preparations, fusion images are numerous, being mostly of small diameter. ADH stimulation produces a moderate increase in the number of fusion images and a significant increase in fusion-image diameter. These findings indicate that the individual particles are mobile within the membrane, lacking interparticle linkage. In addition, contact of cytoplasmic tubules with the luminal membrane may take place even in the absence of ADH, producing small fusion images which are not associated with aggregate delivery to the luminal membrane.

Structural and cytochemical differentiation of membrane elements of the apical membrane of amphibian urinary bladder epithelial cells. A label fracture study

It is now generally accepted that ADH-induced increase in water permeability in responsive epithelia is associated with the insertion of specific structures in the apical membrane of epithelial cells. Up to now, these structures have only been recognized in freeze-fractured preparations and their chemical nature is still unknown. In this study, we used the label-fracture method (Pinto da Silva and Kan, J. Cell Biol., 99, 1156-1161, 1984) to investigate the distribution of wheat germ agglutinin (WGA) on the luminal plasma membrane of freeze-fractured frog urinary bladder epithelial cells. With label-fracture, the cytochemical markers are seen superimposed with the conventional high resolution image of the E face. Label-fracture of tissue treated for 15 min with WGA and subsequently labeled with colloidal gold coated with ovomucoid showed uniform distribution of gold particles along the exoplasmic fracture face. Stereomicrographs show that the gold label is under the fracture face as it is attached to the outer surface of the membrane. Preincubation of the bladder with WGA for 3 hr induced a segregation of the intramembranous particles of the apical plasma membrane. In this condition, we observed a co-distribution of WGA-gold complexes with the segregated particles on the E face. This indicates that WGA-binding sites are located on glycoproteins which probably comprise the large intramembranous particles dispersed on the exoplasmic faces of freeze-fractured luminal membranes. In contrast, the numerous small intramembrane particles observed on P faces remained evenly distributed even after exposure to WGA and are, therefore, unrelated to WGA receptor sites. After WGA treatment, ADH still induced the formation of aggregates inside the smooth domains. A few WGA-binding sites appeared to be associated to these aggregates.

Apical material extracted from amphibian urinary bladder epithelium by enzymes and detergent treatment

The apical plasma membrane of epithelial cells of frog and toad urinary bladder is subject to large modifications during the induction of water permeability by the antidiuretic hormone. A better characterization of the apical membrane is necessary for a clear understanding of the mechanisms of hormone action. Towards this end, apical material was extracted by enzymatic treatment and by incubation with detergent. Proteolytic enzyme alone had little effect under our conditions. A pretreatment with several glycosidases (alpha-mannosidase or endo-beta-N-acetylglucosaminidase H) increased the hydrolytic action of papain, elastase, proteinase K or Staphylococcus aureus V8 protease and allowed the detection of a major 76 kD in SDS gel electrophoresis. The n-octyl-beta-D-glucopyranoside (0.2%) led to the extraction after 150 mn of 1 to 5 micrograms proteins per cm2 of amphibian urinary bladder apical surface. The extracted proteins migrated as several bands on SDS gels. One of them probably corresponds to the 76 kD fragment obtained after proteolysis. The absence of alteration of the water permeability after extraction and the good preservation of the ultrastructure are evidence for the localisation of the 76 kD at the apical membrane surface. This protein may be the best candidate as antigen to raise antibodies against the apical surface of amphibian urinary bladder epithelial cells.

Effects of cellular acidification on ADH-induced intramembrane particle aggregates

8-Bromoadenosine 3',5'-cyclic monophosphate [an analogue of adenosine 3',5'-cyclic monophosphate (cAMP), the intracellular mediator for antidiuretic hormone (ADH) action] induces, in frog urinary bladder, an increase in water permeability that is rapidly and reversibly inhibited by cellular acidification. The effect of CO2 bubbling on the simultaneously observed intramembranous particle aggregates, which probably represent water channels, depended on the time that elapsed after changing medium pH: 3 min of CO2 bubbling depressed the water flux by 70%, whereas the membrane surface occupied by the aggregates remained unchanged. On the contrary, after 9-15 min of CO2 bubbling, both the water flux and the surface area occupied by the aggregates were strongly reduced. These results can be interpreted by accepting two post-cAMP levels of action for cellular acidification: 1) the channels themselves that, as previously suggested by ADH experiments at low temperature, would shift their structure from an "open" to a "closed" state, and 2) the mechanism that controlled the aggregates' plug in and removal.

The single file hypothesis and the water channels induced by antidiuretic hormone

Unidirectional and net water movements were determined at minute intervals in frog urinary bladders. The changes in both parameters were followed, during the action of antidiuretic hormone (ADH), at different temperatures and stirring conditions. After correction for external unstirred layer effects, the ratio of the osmotic (Pf) and diffusional (Pd) permeability coefficients was remarkably constant, at different times and in different experimental conditions. In the presence of ADH the delta Pf/delta Pd ratio in the mucosal border was probably greater than 9. On the other hand, in nonstimulated preparations the ratio was smaller, and probably not different from 1. These results, together with previous observations indicating that other small molecules (like urea) are excluded from the ADH-induced channel, might indicate that single-file water movement can occur through this structure. Alternatively, the delta Pf/delta Pd ratio could result from a complex geometric arrangement in series with the aqueous pore.

Intracellular pH, transepithelial pH gradients, and ADH-induced water channels

Urinary bladders of frogs were exposed to a transepithelial proton and osmotic gradient (serosal pH 8.1, Tris or bicarbonate buffer; mucosal pH 5.8, unbuffered) while the alkalinization rate of the mucosal bath and the net water movement were simultaneously monitored. It was observed that 1) the mucosal alkalinization rate was dependent on serosal pH and buffer; 2) oxytocin increased the mucosal alkalinization rate only when serosal bicarbonate was employed, whereas the net water movement augmented both when serosal bicarbonate or Tris buffers were used; 3) amiloride did not modify the mucosal alkalinization rate either before or after oxytocin; 4) the increases in the mucosal alkalinization rate and in the net water movement induced by oxytocin (serosal bicarbonate) were negatively correlated. In other experiments intracellular pH (pHi) was estimated with the DMO distribution technique with the following results. 1) Oxytocin increased the pHi when either serosal bicarbonate or Tris buffers was used and even in the presence of a low mucosal pH (Tris buffer, pH 5.8). 2) Important cellular acidification was observed when CO2 was bubbled (to pH 5.8), whereas the hydrosmotic response to 8-bromo-cAMP was clearly inhibited. These results indicate that cellular alkalinization could play a pivotal role in action of ADH, show that ADH can modify the transepithelial pH equilibrium mechanism, and suggest that intracellular pH regulation and water permeability control can be linked regulatory processes.

The rate-limiting step in hydrosmotic response of frog urinary bladder

The ADH-induced water fluxes and the associated appearance of intramembranous particle aggregates in the luminal membrane of frog urinary bladders have been correlated in a time course study. Plots of the onset and reversal of the oxytocin-induced hydrosmotic response were sigmoidal in shape, symmetrical and slowed by low temperature to the same degree. Parallel freeze-fracture studies showed that the mean size distribution of the aggregates was constant at different temperatures and at different times during hormonal stimulation and washout. No qualitatively different picture of aggregate formation was detected at low temperature: this suggests that the insertion and removal of individual aggregates into or from the apical plasma membrane is a rather rapid process, both at 20 and at 6.5 degrees C. As in the case of water permeability, both aggregate appearance and disappearance were similarly slowed by lowering the temperature. A similar time-course study of the inhibition of the hydrosmotic response by acidification of the medium was also made. In this case, lowering the incubation temperature induced a clear dissociation between net water flow and the surface area occupied by the aggregates. For the first time, a low water permeability was found associated with a high aggregate surface area in the apical membrane, indicating that cellular acidification induces an impairment of aggregate function rather than a reduction of surface area.

[Traumatic lesions of the nose-ethmoid-forehead region]

The treatment of this kind of lesion further remains difficult and requires work of several specialists: Neurosurgeon, Ophthalmologist, and ENT-surgeon. As for our opinion the reconstruction of anatomy and normal function of the frontal sinus is unequivocal, and performing it in the majority of cases renders in outstanding results.

Detergent extraction of membrane proteins related to the action of antidiuretic hormone

Antidiuretic hormone (ADH) induces, in the apical plasma membrane of target cells, the insertion of intramembranous particle aggregates that probably contain water channels. A mild attack of this membrane by a polyoxyethylene nonylphenyl detergent, which reversibly depressed ADH-induced water permeability, has been found to modify aggregate structure while extracting additional proteins. This simple procedure could be a valuable approach to the problem of aggregate isolation and characterization.

Retention of antidiuretic hormone-induced particle aggregates by luminal membranes separated from toad bladder epithelial cells

Aggregates of intramembrane particles appear in the luminal membranes of renal collecting duct and amphibian bladder cells after stimulation by antidiuretic hormone (ADH). We undertook this freeze-fracture study to determine whether particle aggregates, once in place, remain in the luminal membrane of the amphibian bladder after the membrane is physically separated from the rest of the cell. We found that the aggregates do remain in high yield in isolated membranes stabilized with a bifunctional imidoester (DTBP) followed by fixation with glutaraldehyde, or unfixed but stabilized with DTBP. These findings support the view that the particles are intrinsic membrane components and that their organization in the form of aggregates does not depend on the presence of the intact cell. In addition, the availability of isolated membranes containing particle aggregates provides a starting point for the isolation of the water-conducting proteins.

Cellular pH and water permeability control in frog urinary bladder. A possible action on the water pathway

Mucosal acidification (from pH 8.1 to 6.0) reversibly inhibited the hydroosmotic responses to oxytocin, cyclic AMP and 8-bromo-cyclic AMP in frog urinary bladder. These inhibitory effects were only observed in the presence of a permeant buffer in the apical medium and could also be elicited by CO2 bubbling, even when the mucosal pH was clamped at 8.1. Acid pH reduced the oxytocin-induced net water flux faster than norepinephrine or oxytocin removal and the difference was especially important at low temperature. The time course of recovery from acid pH inhibition was, at 20 degree C, similar to that of the hormonal action, but when the medium temperature was reduced to 6-7 degrees C, the recovery from acid pH inhibition paradoxically became faster while the oxytocin action was markedly slowed down (t 1/2 of changes in net water fluxes (expressed in min): oxytocin addition at 20 degrees C, 6.2 +/- 0.9; at 6 degrees C, 24 +/- 3; oxytocin removal at 20 degrees C, 4.7 +/- 0.8; at 6 degrees C, 22 +/- 3; pH inhibition at 20 degrees C, 2.6 +/- 0.2, at 6 degrees C 2.5 +/- 0.2; recovery from pH 6 at 20 degrees C 6.5 +/- 0.9; at 6 degrees C, 2.7 +/- 0.3). These results can be explained by accepting two main loci sensitive to medium acidification: (1) the cyclase system and (2) an intracellular, temperature-independent, post-cyclic AMP site. The fact that the intramembranous particle aggregates associated with the oxytocin-induced water permeability increase did not disappear after the flow inhibition by acid pH at low temperature suggests that the second effect could be located at the water channel itself.

Fine structure of intramembranous particle aggregates in ADH-treated frog urinary bladder and skin: influence of glutaraldehyde and N-ethyl maleimide

The fine structure of ADH-induced intramembrane particle aggregates has been studied in different tissues and under different experimental conditions. Particle aggregates similar to those previously observed in the amphibian urinary bladder and in the mammalian collecting duct were also found in the frog skin, another ADH target tissue. In the frog urinary bladder, typical aggregates were observed in the absence of glutaraldehyde fixation. Two experimental approaches were used 1) the absence of both fixative and cryoprotectant treatments and b) the absence of only glutaraldehyde treatment. In the latter case the reversal of hydrosmotic action was prevented by exposing the preparations to N-ethyl maleimide. In specimens of frog urinary bladder conventionally fixed with glutaraldehyde, two fracture levels could be observed in the aggregates, suggesting that the aggregated particles span an appreciable part of the membrane thickness.

Effects of pentoxifylline and various methylxanthine derivatives on transepithelial water permeability of frog urinary bladder

Theophylline, pentoxifylline and MIX (isobutyl methylxanthine) increase the water permeability of frog urinary bladder when added to the serosal side of the epithelium; this hydrosmotic effect is explained by an inhibition of adenylate cyclase. Both pentoxifylline and MIX exhibit an higher biological activity than theophylline. In contrast to theophylline, pentoxifylline and MIX stimulate the water permeability when added to the mucosal side of the epithelium; this probably results from a better penetration of these drugs into cells.

[Esophagotracheal fistula after tracheotomy and assisted ventilation (author's transl)]

On the basis of 12 cases of oesophagotracheal fistula after tracheotomy and assisted ventilation, the authors discuss the etiopathogenesis and the diagnosis of this grave condition, emphasizing its inevitably surgical treatment, and the major value of prophylaxis which is nevertheless difficult to apply.

[Fronto-ethmoidal meningo-encephaloceles and nasal gliomas (author's transl)]

Meningoencephalocoeles and nasal gliomas are congenital malformations rare in Europe but much better known in Morocco and in Thailand. These lesions have embryonic relations which are such that certain authors consider them to be only clinical varieties of the same malformation. They cause extra nasal, intra nasal or mixed tumours discovered most often at birth. Treatment is surgical either via a high intracranial approach or via a low facial approach (both approaches sometimes being used in association) and the prognosis is dominated by the problem of the dura mater if there are connections between the tumour mass and the subarachnoid spaces. When the problem is resolved by dural plasty, the later prognosis is excellent and, in particular, the psychomotor development of the children appears to be normal. Cosmetic problems, and in particular hypertelorism, may nevertheless require later surgery.

[On 30 cases of naso-pharyngeal fibromas (author's transl)]

The authors report their experiments in the diagnosis and treatment of naso-pharyngeal fibromas. They point out:--the usefulness of tomo-densitometric and arteriographic examinations; but they are concerned by the neurological dangers of embolization;--the usefulness of surgical treatment in this condition, usually done by the infralabial route, in the Rouge-Denker technique.

Influence of mucosal and serosal pH on antidiuretic action in frog urinary bladder

Mucosal acidification to pH 6.5 reduced by 88% the oxytocin- (2.2 x 10(-8) M) elicited increase of water permeability in frog urinary bladder. Mucosal alkalinization (pH 10.5) increased by as much as 200% the response to the same concentration of oxytocin. These effects were not observed when supramaximal concentrations of oxytocin were imployed. Similar changes were found when the serosal pH was modified. The hydrosmotic responses elicited by serosal hypertonicity or cyclic AMP plus theophylline were also affected by mucosal or serosal changes of the hydrogen in concentration, suggesting an effect at a post-cyclic AMP level. Important interactions were found between luminal pH and serosal hypertonicity when experimental conditions were employed similar to those observed in the collecting duct of mammalian nephron. Freeze-fracture studies showed that the number of intramembranous aggregates of particles induced by ADH in the luminal membrane was reduced by mucosal acidification and augmented by an increase in medium pH.