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Vincent E Dionne - One of the best experts on this subject based on the ideXlab platform.
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two second messengers mediate amino acid responses in olfactory sensory neurons of the salamander Necturus Maculosus
Chemical Senses, 2002Co-Authors: Rona J Delay, Vincent E DionneAbstract:Odor transduction mediated by the adenylyl cyclase/cAMP pathway has been well studied, but it is still uncertain whether this pathway mediates the transduction of all odors in vertebrates. We isolated olfactory sensory neurons from the salamander Necturus Maculosus and used calcium imaging with the indicator dye fura-2 to examine olfactory responses elicited by amino acids. The properties of approximately two-thirds of the odor responses suggested they were mediated by the adenylyl cyclase/ cAMP pathway, but one-third of the responses were not mimicked by cAMP analogs nor blocked by inhibition of adenylyl cyclase, suggesting that these odor responses were mediated differently. Responses that were unaffected by inhibition of adenylyl cyclase were blocked by neomycin, an inhibitor of phospholipase C, implying that they were transduced by activation of phospholipase C. Some cells which responded to more than one amino acid appeared to employ both pathways, but each was used to transduce different odors. In addition, many responses that were mediated by the adenylyl cyclase/cAMP pathway were enhanced following inhibition of phospholipase C, suggesting that the phospholipase C pathway has a role not only in odor transduction, but also in the modulation of olfactory responses.
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modulation of cl k and nonselective cation conductances by taurine in olfactory receptor neurons of the mudpuppy Necturus Maculosus
The Journal of General Physiology, 1993Co-Authors: Adrienne E Dubin, Vincent E DionneAbstract:Odors are transduced by processes that modulate the membrane conductance of olfactory receptor neurons. Olfactory neurons from the aquatic salamander, Necturus Maculosus, were acutely isolated without enzymes and studied with a resistive whole-cell method to minimize loss of soluble intracellular constituents. 55 of 224 neurons responded to the test compound taurine at concentrations between 10 nM and 100 microM. Four different conductance changes were elicited by taurine: an increased Cl- conductance (33%), an increased nonselective cation conductance (15%), a decreased Cl- conductance (15%), and a decreased K+ conductance (15%); in addition, responses too small to be characterized were elicited in some neurons. In most cases, taurine appeared to modulate only a single conductance in any particular cell. Modulation of each conductance was dose dependent, and each response ran down quickly in the normal whole-cell mode, presumably due to washout of a diffusible component in the transduction pathway. Modulation of taurine-sensitive conductances caused either inhibitory or excitatory responses. A similar diversity of responses in vivo would produce a complex pattern of electrical activity that could encode the identity and characteristics of an odor.
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chemosensory responses in isolated olfactory receptor neurons from Necturus Maculosus
The Journal of General Physiology, 1992Co-Authors: Vincent E DionneAbstract:Olfactory receptor neurons were isolated without enzymes from the mudpuppy, Necturus Maculosus, and tested for chemosensitivity. The cells responded to odorants with changes in firing frequency and alterations in excitability that were detected with tight-seal patch electrodes using on-cell and whole-cell recording conditions. Chemosensitive cells exhibited two primary response characteristics: excitation and inhibition. Both types of primary response were observed in different cells stimulated by mixtures of amino acids as well as by the single compound L-alanine, suggesting that there may be more than one transduction pathway for some odorants. Using the normal whole-cell recording method, the chemosensitivity of competent cells washed out rapidly; a resistive whole-cell method was used to record odorant responses under current-clamp conditions. In response to chemical stimulation, excitability appeared to be modulated in several different ways in different cells: odorants induced hyperpolarizing or depolarizing receptor potentials, elicited or inhibited transient, rhythmic generator potentials, and altered excitability without changing the membrane potential or input resistance. These effects suggest that olfactory transduction is mediated through at least three different pathways with effects on four or more components of the membrane conductance. Polychotomous pathways such as these may be important for odor discrimination and for sharpening the "odor image" generated in the olfactory epithelium.
Virginie Vlaeminckguillem - One of the best experts on this subject based on the ideXlab platform.
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pedomorphosis revisited thyroid hormone receptors are functional in Necturus Maculosus
Evolution & Development, 2006Co-Authors: Rachid Safi, Virginie Vlaeminckguillem, Martine Duterquecoquillaud, Marilyne Duffraisse, Isabelle Seugnet, Michelina Plateroti, Alain Margotat, Erica J Crespi, Robert J DenverAbstract:SUMMARY Heterochrony, a difference in developmental timing, is a central concept in modern evolutionary biology. An example is pedomorphosis, retention of juvenile characteristics in sexually mature adults, a phenomenon largely represented in salamanders. The mudpuppy (Necturus Maculosus) is an obligate pedomorphic amphibian, never undergoing metamorphosis. Thyroid hormone induces tissue transformation in metamorphosing species and this action is mediated by nuclear thyroid hormone (TH) receptors (TRs). The absence of metamorphosis in Necturus has been attributed to a resistance to TH action as treatment with exogenous TH fails to induce transformation. The failure to metamorphose could be due to the lack of TR expression in target tissues, or to a loss of TR function. Toward understanding the molecular basis for the failure of Necturus tissues to respond to TH, and the ultimate cause for the expression of the obligate pedomorphic life history, we characterized the structure, function, and expression of TR genes in Necturus. Strikingly, we found that Necturus TRα and TRβ genes encode fully functional TR proteins. These TRs bind both DNA and TH and can transactivate target genes in response to TH. Both TRα and TRβ are expressed in various tissues. TH treatment in vivo induced expression in the gill of some but not all genes known to be activated by TH in anuran larvae, caused whole organism metabolic effects, but induced no external morphological changes in adults or larvae. Thus, Necturus possesses fully functional TRs and its tissues are not generally resistant to the actions of TH. Rather, the absence of metamorphosis may be due to the loss of TH-dependent control of key genes required for tissue transformation.
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thyroid hormone receptor expression in the obligatory paedomorphic salamander Necturus Maculosus
The International Journal of Developmental Biology, 2006Co-Authors: Virginie Vlaeminckguillem, Rachid Safi, Philippe Guillem, Emmanuelle Leteurtre, Martine Duterquecoquillaud, Vincent LaudetAbstract:Amphibian metamorphosis is under the strict control of thyroid hormones (TH). These hormones induce metamorphosis by controlling gene expression through binding to thyroid hormone receptors (TRs). Necturus Maculosus is considered to be an obligatory paedomorphic Amphibian since metamorphosis never occurs spontaneously and cannot be induced by pharmacological means. Since metamorphosis depends on the acquisition of response of tadpole tissues to thyroid hormone, we aimed to determine TR gene expression patterns in Necturus Maculosus as well as the expression of two TH-related genes: Cytosolic Thyroid Hormone-Binding Protein (CTHBP)-M2-pyruvate kinase, a gene encoding a cytosolic TH binding protein and stromelysin 3, a direct TH target gene in Xenopus laevis. Tissue samples were obtained from specimens of Necturus Maculosus. We performed in situ hybridization using non-cross-hybridizing RNA probes obtained from the cloned Necturus TRalpha and TRbeta genes. We found clear expression of Necturus TRalpha gene in several tissues including the central nervous system, epithelial cells of digestive and urinary organs, as well as myocardium and skeletal muscle. TRbeta was also expressed in the brain. In other tissues, hybridization signals were too low to draw reliable conclusions about their precise distribution. In addition, we observed that the expression of CTHBP and ST3 is largely distinct from that of TRs. The fact that we observed a clear expression of TRalpha and TRbeta which are evolutionary conserved, suggests that Necturus tissues express TRs. Our results thus indicate that, in contrast to previously held hypotheses, Necturus tissues are TH responsive.
Janez Scancar - One of the best experts on this subject based on the ideXlab platform.
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Hepatic metallothioneins in two neotenic salamanders, Proteus anguinus and Necturus Maculosus (Amphibia, Caudata).
Comparative biochemistry and physiology. Toxicology & pharmacology : CBP, 2020Co-Authors: K Dobrovoljc, Ingrid Falnoga, Boris Bulog, M Tusek-znidaric, Janez ScancarAbstract:The presence of metallothionein (MT) and the subcellular distribution of copper, zinc and cadmium were investigated in livers of two neotenic salamanders, Proteus anguinus and Necturus Maculosus. In P. anguinus, caught in the wild, hepatic MTs were present as a single isoform of (Zn, Cu, Cd)-thioneins, whose molecular weight was estimated to be approximately 12000 by size exclusion chromatography. The percentage of zinc and cadmium was higher in the cytosol and of copper in the pellet. Cytosolic cadmium was almost exclusively associated with MTs (80%), while zinc and copper were also present in the regions of higher-molecular weight proteins. In laboratory bred N. Maculosus, MTs were isolated from the liver cytosol and extract of the pellet as (Cu, Zn)- and (Zn, Cu)-thioneins, respectively. According to the low amount of copper extracting from liver pellets of N. Maculosus, the presence of water insoluble aggregated forms of Cu-thioneins should be checked in further investigations.
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cd cu zn se and metallothioneins in two amphibians Necturus Maculosus amphibia caudata and bufo bufo amphibia anura
Biological Trace Element Research, 2012Co-Authors: Katarina Dobrovoljc, Ingrid Falnoga, Janez Scancar, Magda Tusek žnidaric, Darja Mazej, Boris BulogAbstract:The accumulation of cadmium, its affinity for metallothioneins (MTs), and its relation to copper, zinc, and selenium were investigated in the experimental mudpuppy Necturus Maculosus and the common toad Bufo bufo captured in nature. Specimens of N. Maculosus were exposed to waterborne Cd (85 μg/L) for up to 40 days. Exposure resulted in tissue-dependent accumulation of Cd in the order kidney, gills > intestine, liver, brain > pancreas, skin, spleen, and gonads. During the 40-day exposure, concentrations increased close to 1 μg/g in kidneys and gills (0.64–0.95 and 0.52–0.76; n = 4), whereas the levels stayed below 0.5 in liver (0.14–0.29; n = 4) and other organs. Cd exposure was accompanied by an increase of Zn and Cu in kidneys and Zn in skin, while a decrease of Cu was observed in muscles and skin. Cytosol metallothioneins (MTs) were detected as Cu,Zn–thioneins in liver and Zn,Cu–thioneins in gills and kidney, with the presence of Se in all cases. After exposure, Cd binding to MTs was clearly observed in cytosol of gills as Zn,Cu,Cd–thionein and in pellet extract of kidneys as Zn,Cu,Cd–thioneins. The results indicate low Cd storage in liver with almost undetectable Cd in liver MT fractions. In field trapped Bufo bufo (spring and autumn animals), Cd levels were followed in four organs and found to be in the order kidney > liver (0.56–5.0 μg/g >0.03–0.72 μg/g; n = 11, spring and autumn animals), with no detectable Cd in muscle and skin. At the tissue level, high positive correlations between Cd, Cu, and Se were found in liver (all r > 0.80; α = 0.05, n = 5), and between Cd and Se in kidney (r = 0.76; n = 5) of autumn animals, possibly connected with the storage of excess elements in biologically inert forms. In the liver of spring animals, having higher tissue level of Cd than autumn ones, part of the Cd was identified as Cu,Zn,Cd–thioneins with traces of Se. As both species are special in having liver Cu levels higher than Zn, the observed highly preferential Cd load in kidney seems reasonable. The relatively low Cd found in liver can be attributed to its excretion through bile and its inability to displace Cu from MTs. The associations of selenium observed with Cd and/or Cu (on the tissue and cell level) point to selenium involvement in the detoxification of excessive cadmium and copper through immobilization.
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hepatic metallothioneins in two neotenic salamanders proteus anguinus and Necturus Maculosus amphibia caudata
Comparative Biochemistry and Physiology C-toxicology & Pharmacology, 2003Co-Authors: K Dobrovoljc, Ingrid Falnoga, Boris Bulog, Majda Tusekžnidaric, Janez ScancarAbstract:b ˇ Abstract The presence of metallothionein (MT) and the subcellular distribution of copper, zinc and cadmium were investigated in livers of two neotenic salamanders, Proteus anguinus and Necturus Maculosus .I nP. anguinus, caught in the wild, hepatic MTs were present as a single isoform of (Zn, Cu, Cd)-thioneins, whose molecular weight was estimated to be approximately 12 000 by size exclusion chromatography. The percentage of zinc and cadmium was higher in the cytosol and of copper in the pellet. Cytosolic cadmium was almost exclusively associated with MTs (80%), while zinc and copper were also present in the regions of higher-molecular weight proteins. In laboratory bred N. Maculosus, MTs were isolated from the liver cytosol and extract of the pellet as (Cu, Zn)- and (Zn, Cu)-thioneins, respectively. According to the low amount of copper extracting from liver pellets of N. Maculosus, the presence of water insoluble aggregated forms of Cu-thioneins should be checked in further investigations. 2003 Elsevier Inc. All rights reserved.
Boris Bulog - One of the best experts on this subject based on the ideXlab platform.
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Hepatic metallothioneins in two neotenic salamanders, Proteus anguinus and Necturus Maculosus (Amphibia, Caudata).
Comparative biochemistry and physiology. Toxicology & pharmacology : CBP, 2020Co-Authors: K Dobrovoljc, Ingrid Falnoga, Boris Bulog, M Tusek-znidaric, Janez ScancarAbstract:The presence of metallothionein (MT) and the subcellular distribution of copper, zinc and cadmium were investigated in livers of two neotenic salamanders, Proteus anguinus and Necturus Maculosus. In P. anguinus, caught in the wild, hepatic MTs were present as a single isoform of (Zn, Cu, Cd)-thioneins, whose molecular weight was estimated to be approximately 12000 by size exclusion chromatography. The percentage of zinc and cadmium was higher in the cytosol and of copper in the pellet. Cytosolic cadmium was almost exclusively associated with MTs (80%), while zinc and copper were also present in the regions of higher-molecular weight proteins. In laboratory bred N. Maculosus, MTs were isolated from the liver cytosol and extract of the pellet as (Cu, Zn)- and (Zn, Cu)-thioneins, respectively. According to the low amount of copper extracting from liver pellets of N. Maculosus, the presence of water insoluble aggregated forms of Cu-thioneins should be checked in further investigations.
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Isolation and primary culture of Necturus Maculosus (Amphibia: Urodela) hepatocytes.
In vitro cellular & developmental biology. Animal, 2020Co-Authors: Petramaja Prelovsek, Urska Batista, Boris BulogAbstract:In order to evaluate their suitability for physiological and ecotoxicological studies, hepatocytes were isolated from the common mudpuppy (Necturus Maculosus) using a two-step collagenase perfusion. Hepatocytes in primary culture were investigated for 14 d using light and electron microscopy and biochemical analyses. A typical perfusion yielded 1.7 x 10(5) viable hepatocytes per gram body weight with an average viability of 86 +/- 5%. The majority of isolated cells remained in suspension and formed aggregates. The viability of hepatocytes in primary culture was dependent on a fetal calf serum (FCS) concentration and incubation temperature. Viability was best at 8 degrees C in Leibovitz L-15 medium supplemented with 5% FCS. The ultrastructural characteristics of freshly isolated hepatocytes resembled those of N. Maculosus hepatocytes in vivo. Whereas hepatocyte viability remained relatively stable (around 80%) up to 14 d in culture, electron microscopic analyses revealed changes at ultrastructural level. The majority of hepatocytes retained similar structural characteristics to those in vivo up to 4 d. Loss of cellular polarity, fractionation of rough endoplasmic reticulum, formation of autophagosomes, and successive exhaustion of cellular glycogen deposits were observed with increased time in culture. Functional integrity, as estimated by tyrosine aminotransferase induction, decreased during the culture period. Ultrastructural and biochemical analyses indicate the need for further improvement of culture conditions. Nevertheless, isolated hepatocytes in primary culture for up to 4 d can be recommended as a model for physiological and toxicological studies in lower vertebrates.
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cd cu zn se and metallothioneins in two amphibians Necturus Maculosus amphibia caudata and bufo bufo amphibia anura
Biological Trace Element Research, 2012Co-Authors: Katarina Dobrovoljc, Ingrid Falnoga, Janez Scancar, Magda Tusek žnidaric, Darja Mazej, Boris BulogAbstract:The accumulation of cadmium, its affinity for metallothioneins (MTs), and its relation to copper, zinc, and selenium were investigated in the experimental mudpuppy Necturus Maculosus and the common toad Bufo bufo captured in nature. Specimens of N. Maculosus were exposed to waterborne Cd (85 μg/L) for up to 40 days. Exposure resulted in tissue-dependent accumulation of Cd in the order kidney, gills > intestine, liver, brain > pancreas, skin, spleen, and gonads. During the 40-day exposure, concentrations increased close to 1 μg/g in kidneys and gills (0.64–0.95 and 0.52–0.76; n = 4), whereas the levels stayed below 0.5 in liver (0.14–0.29; n = 4) and other organs. Cd exposure was accompanied by an increase of Zn and Cu in kidneys and Zn in skin, while a decrease of Cu was observed in muscles and skin. Cytosol metallothioneins (MTs) were detected as Cu,Zn–thioneins in liver and Zn,Cu–thioneins in gills and kidney, with the presence of Se in all cases. After exposure, Cd binding to MTs was clearly observed in cytosol of gills as Zn,Cu,Cd–thionein and in pellet extract of kidneys as Zn,Cu,Cd–thioneins. The results indicate low Cd storage in liver with almost undetectable Cd in liver MT fractions. In field trapped Bufo bufo (spring and autumn animals), Cd levels were followed in four organs and found to be in the order kidney > liver (0.56–5.0 μg/g >0.03–0.72 μg/g; n = 11, spring and autumn animals), with no detectable Cd in muscle and skin. At the tissue level, high positive correlations between Cd, Cu, and Se were found in liver (all r > 0.80; α = 0.05, n = 5), and between Cd and Se in kidney (r = 0.76; n = 5) of autumn animals, possibly connected with the storage of excess elements in biologically inert forms. In the liver of spring animals, having higher tissue level of Cd than autumn ones, part of the Cd was identified as Cu,Zn,Cd–thioneins with traces of Se. As both species are special in having liver Cu levels higher than Zn, the observed highly preferential Cd load in kidney seems reasonable. The relatively low Cd found in liver can be attributed to its excretion through bile and its inability to displace Cu from MTs. The associations of selenium observed with Cd and/or Cu (on the tissue and cell level) point to selenium involvement in the detoxification of excessive cadmium and copper through immobilization.
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isolation and primary culture of Necturus Maculosus amphibia urodela hepatocytes
In Vitro Cellular & Developmental Biology – Animal, 2006Co-Authors: Petramaja Prelovsek, Urska Batista, Boris BulogAbstract:In order to evaluate their suitability for physiological and ecotoxicological studies, hepatocytes were isolated from the common mudpuppy (Necturus Maculosus) using a two-step collagenase perfusion. Hepatocytes in primary culture were investigated for 14 d using light and electron microscopy and biochemical analyses. A typical perfusion yielded 1.7×105 viable hepatocytes per gram body weight with an average viability of 86±5%. The majority of isolated cells remained in suspension and formed aggregates. The viability of hepatocytes in primary culture was dependent on a fetal calf serum (FCS) concentration and incubation temperature. Viability was best at 8°C in Leibovitz L-15 medium supplemented with 5% FCS. The ultrastructural characteristics of freshly isolated hepatocytes resembled those of N. Maculosus hepatocytes in vivo. Whereas hepatocyte viability remained relatively stable (around 80%) up to 14 d in culture, electron microscopic analyses revealed changes at ultrastructural level. The majority of hepatocytes retained similar structural characteristics to those in vivo up to 4 d. Loss of cellular polarity, fractionation of rough endoplasmic reticulum, formation of autophagosomes, and successive exhaustion of cellular glycogen deposits were observed with increased time in culture. Functional integrity, as estimated by tyrosine aminotransferase induction, decreased during the culture period. Ultrastructural and biochemical analyses indicate the need for further improvement of culture conditions. Nevertheless, isolated hepatocytes in primary culture for up to 4 d can be recommended as a model for physiological and toxicological studies in lower vertebrates.
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hepatic metallothioneins in two neotenic salamanders proteus anguinus and Necturus Maculosus amphibia caudata
Comparative Biochemistry and Physiology C-toxicology & Pharmacology, 2003Co-Authors: K Dobrovoljc, Ingrid Falnoga, Boris Bulog, Majda Tusekžnidaric, Janez ScancarAbstract:b ˇ Abstract The presence of metallothionein (MT) and the subcellular distribution of copper, zinc and cadmium were investigated in livers of two neotenic salamanders, Proteus anguinus and Necturus Maculosus .I nP. anguinus, caught in the wild, hepatic MTs were present as a single isoform of (Zn, Cu, Cd)-thioneins, whose molecular weight was estimated to be approximately 12 000 by size exclusion chromatography. The percentage of zinc and cadmium was higher in the cytosol and of copper in the pellet. Cytosolic cadmium was almost exclusively associated with MTs (80%), while zinc and copper were also present in the regions of higher-molecular weight proteins. In laboratory bred N. Maculosus, MTs were isolated from the liver cytosol and extract of the pellet as (Cu, Zn)- and (Zn, Cu)-thioneins, respectively. According to the low amount of copper extracting from liver pellets of N. Maculosus, the presence of water insoluble aggregated forms of Cu-thioneins should be checked in further investigations. 2003 Elsevier Inc. All rights reserved.
Thomas Zeuthen - One of the best experts on this subject based on the ideXlab platform.
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cotransport of k cl and h2o by membrane proteins from choroid plexus epithelium of Necturus Maculosus
The Journal of Physiology, 1994Co-Authors: Thomas ZeuthenAbstract:1. The interaction between K+, Cl- and H2O fluxes was studied in the ventricular membrane of the choroid plexus epithelium from Necturus Maculosus by means of ion-selective microelectrodes. 2. Three experimental strategies were adopted: the osmolarity of the ventricular solution was increased abruptly by addition of (i) mannitol or (ii) KCl; (iii) Na+ in the ventricular solution was replaced isosmotically by K+. 3. The mannitol experiments showed that H2O had two pathways across the ventricular membrane. One was purely passive, with a water permeability, L'p, of 0.64 x 10(-4) cm s-1 (osmol l-1)-1. This operated in parallel with an ion-dependent pathway of similar magnitude which was abolished in Cl(-)-free solutions. 4. When KCl was added there was a flow of H2O into the cell. Surprisingly, this took place despite the osmotic gradient which favoured an efflux of H2O. The effect was blocked by frusemide (furosemide), in which case KCl had the same effects as applications of NaCl or mannitol. 5. Replacement of Na+ with K+ caused an influx of H2O. This flux could proceed against osmotic gradients implemented by mannitol. 6. The present data and those of earlier publications show that the interdependence of the fluxes of K+, Cl- and H2O in the exit membrane can be described as cotransport. The fluxes have a fixed stoichiometry of 1:1:500, the flux of one species is able to energize the flux of the two others, and the transport exhibits saturation and is specific for K+ and Cl-. 7. A molecular model based upon a mobile barrier in a membrane spanning protein gives an accurate quantitative description of the data.
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water permeability of ventricular cell membrane in choroid plexus epithelium from Necturus Maculosus
The Journal of Physiology, 1991Co-Authors: Thomas ZeuthenAbstract:1. The osmotic water permeability Lp and the relations between the flows of H2O, K+ and Cl- were studied in the ventricular membrane of the epithelium from the choroid plexus of Necturus Maculosus. 2. The flows were induced by abrupt changes in external osmolarity of the ventricular solution. Solution changes were convective and no effects of unstirred layers could be detected on measured parameters. 3. The initial rate of change in intracellular concentrations of K+ and Cl- was monitored by double-barrelled ion-selective microelectrodes. 4. The initial rate of flux of H2O could be monitored as the changes in the concentration of intracellular choline ions (Ch+i). When 0.5 mmol l-1 of choline chloride was added to the external solutions, Ch+i attained values of 1-5 mmol l-1. The dilution or concentration of Ch+i could be recorded by K+ electrodes since the sensitivity of these to Ch+ is more than 50 times greater than to K+. 5. The Lp of the ventricular membrane of the epithelium was 1.4-2.1 x 10(-4) cm s-1 (osmol l-1)-1 and independent of the direction of the induced water flux. Lp was unchanged in tissues adapted to osmolarities of half the physiological value. 6. The efflux of H2O induced by mannitol was associated with an instantaneous efflux of K+ which was inhibited by furosemide. The fluxes had a ratio of 40 mmol l-1. The influx of H2O induced by the removal of NaCl from the ventricular solution was associated with an instantaneous influx of K+. The H2O influx had a ratio to the flux of K+ of 70 mmol l-1. 7. The efflux of H2O induced by mannitol was associated with an efflux of Cl- which was inhibited by furosemide. The ratio of the two fluxes was in the range 15-44 mmol l-1. 8. The conclusion is that the Ch+ method gives a reliable measure of the movement of H2O across the ventricular membrane. The magnitude of the Lp and its relevance to transepithelial transport are discussed. The osmotically induced H2O movement is accompanied by furosemide-sensitive fluxes of K+ and Cl- of the same magnitude. This suggests that co-transport between H2O and KCl can take place in the membrane.
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secondary active transport of water across ventricular cell membrane of choroid plexus epithelium of Necturus Maculosus
The Journal of Physiology, 1991Co-Authors: Thomas ZeuthenAbstract:1. The interaction between Cl-, K+ and H2O fluxes were studied in the ventricular membrane of the choroid plexus epithelium from Necturus Maculosus by means of ion-selective microelectrodes. The flux of H2O was measured by means of K+ electrodes as the dilution or concentration of intracellular choline ions, Ch+i. 2. In one series of experiments Cl- was readministered to the ventricular solution of tissues incubated in media with low Cl- concentrations. The resulting influx of Cl- was associated with an instantaneous influx of K+ and H2O. 3. Both the Cl- and the K+ influxes were reduced by the diuretic furosemide but were unaffected by inhibitors of Na+, K(+)-ATPase or changes in membrane potentials induced by Ba2+. Since the influx of K+ proceeds against its electrochemical gradient and is unaffected by changes in membrane potentials, the membrane exhibits secondary active, electroneutral transport of K+. 4. The influx of water, initiated simultaneously with the influx of K+ and Cl-, commenced before these ions had changed the osmolarity of the intracellular solution significantly. The influx of H2O could proceed against an osmotic gradient. The influx stopped when 100 mmol l-1 of mannitol was added to the ventricular solution at the same time as the Cl- ions. The influx of H2O was inhibited by K+ removal, furosemide or high external Ba2+ (10 mmol l-1), but not by strophanthidin, ouabain or low concentrations of Ba2+ (0.5 mmol l-1). The influx could not continue with other permeable anions, NO3-, acetate- or SCN-, replacing Cl-. 5. In another series of experiments Cl- was removed from the ventricular solution of tissues bathed in saline solutions with normal concentrations of Cl-. The resulting efflux of Cl- was associated with an instantaneous efflux of K+ and H2O. This efflux of H2O could proceed against an osmotic gradient of up to 70 mosmol l-1. This effect was inhibited by furosemide, in which case the water fluxes were entirely dependent on the osmotic gradients and the osmotic water permeability Lp of the ventricular membrane. 6. The data suggest that there is a coupling between the flux of KCl and of water in the ventricular membrane, which implies that the reflection coefficient sigma for KCl under the given circumstances is less than one. I suggest that the ability of leaky epithelia to transport against osmotic gradients depends on such a coupling, which derives from the properties of the proteins through which K+, Cl- and H2O leave the cell.
