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  • 1
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (71 Seiten = 2,6 MB) , Illustrationen, Graphen, Karten
    Edition: 2021
    Language: German
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    ISSN: 1432-2013
    Keywords: Key words Osmoregulation ; Regulatory volume decrease ; Cytosolic calcium ; Calcium stores ; IP3 ; Arachidonic acid ; Collecting duct
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In rat inner medullary collecting duct (IMCD) cells in primary culture, hypotonic stress induces Ca2+ transients consisting of an early peak phase caused by a Ca2+ release from intracellular stores and a subsequent plateau phase that involves Ca2+ entry from the extracellular milieu. In the present study, the mechanisms by which cell swelling is transduced into the Ca2+ release were investigated. The free intracellular Ca2+ concentration ([Ca2+]i) was measured using the fluorescent dye fura-2 and cell volume using a confocal laser scanning microscope. In control experiments, after reduction of extracellular osmolarity from 600 to 300 mosmol/l, by omission of sucrose, [Ca2+]i rapidly increased from 106 ± 9 nmol/l to a peak value of 405 ± 22 nmol/l (P≤ 0.05) and thereafter reached a steady-state of 230 ± 23 nmol/l. In low-Ca2+ conditions (10 nmol/l), the reduction of osmolarity evoked only a transient increase of [Ca2+]i by 182 ± 11 nmol/l (P≤ 0.05), which reflected Ca2+ release from intracellular stores. Hyposmotic stress had no effect on inositol 1,4,5-triphosphate (IP3) production measured by a [3H]IP3 radioreceptor assay. Preincubation with 100 μmol/l ETYA (a non-metabolisible derivative of arachidonic acid) reduced the Ca2+ response to hyposmotic stress under high and low Ca2+ conditions (87 and 85% inhibition respectively) as well as the regulatory volume decrease (RVD). Extracellular application of arachidonic acid in isotonic medium led to an increase in [Ca2+]i under high and low Ca2+ conditions. Pretreatment of IMCD cells with 50 μg/ml D609 (a phosphatidylcholine-directed phospholipase C inhibitor) or with 200 μmol/l propranolol (a phosphatidate phosphohydrolase inhibitor) reduced the hypotonic Ca2+ response more strongly than pretreatment with 5 μmol/l BPhB (a phospholipase A2 inhibitor). The Ca2+ response was also suppressed after preincubation with 200 μmol/l RHC 80267 (a diacylglycerol lipase inhibitor). Preincubation with 50 ng/ml pertussis toxin (a G-protein inhibitor) reduced the transient component of the Ca2+ response partially. We conclude that G-proteins, phosphatidylcholine-directed phospholipase C, phospholipase A2, diacylglycerol lipase and arachidonic acid, but not IP3, are involved in the mechanisms by which Ca2+ is released from the intracellular stores during RVD in IMCD cells.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2013
    Keywords: Liver Cell volume regulation Na+ conductance Na+/H+ antiport Na+-K+-2Cl– symport Na+/K+-ATPase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The initial event in the regulatory volume increase (RVI) of rat hepatocytes is an influx of Na+ that is then exchanged for K+ via stimulation of Na+/K+-adenosine triphosphatase (ATPase). In this study, we analysed the activation pattern of the Na+ transporters underlying RVI as a function of the degree of hypertonic stress. In confluent primary cultures, four hypertonic conditions were tested (changes from 300 to 327, 360, 400 or 450 mosmol/l) and the activities of Na+ conductance, Na+/H+ antiport, Na+-K+-2Cl– symport and Na+/K+-ATPase were quantified using intracellular microelectrodes, microfluorometry and time-dependent, furosemide- or ouabain-sensitive 86Rb+ uptake, respectively. Neither Na+ conductance nor Na+-K+-2Cl– symport responded to 327 mosmol/l. At 360, 400 and 450 mosmol/l, uptake via these transporters would lead to increases of cell Na+ by 33.0, 49.0 and 49.0 and by 4.5, 10.4 and 9.2 mmol/l per 10 min, respectively. In contrast, Na+/H+ antiport exhibited 65% of its maximal activation already at 327 mosmol/l. At the four osmolarities tested, this transporter would augment cell Na+ by 6.9, 8.9, 9.8 and 10.6 mmol/l per 10 min. The sums of Na+ import were consistent with the amounts of Na+ exported via Na+/K+-ATPase plus the actual increases of cell Na+ (21.2, 58.5, 63.6 and 68.3 mmol/l per 10 min and 2.2, 4.0, 6.3 and 8.2 mmol/l, respectively). In addition, these elevations of cell Na+ plus the increases of cell K+ (via Na+/K+-ATPase) that amounted to 5.0, 6.5, 17.5 and 18.4 mmol/l were consistent with the increases of intracellular osmotic (cationic) activity of 2.5, 11.5, 21.0 and 28.5 mmol/l, respectively, computed from RVI data. It is concluded that the principle of rat hepatocyte RVI, i.e. an initial uptake of Na+ that is then exchanged for K+ via Na+/K+-ATPase, is realized over the entire range of 9-50% hypertonicity tested. The set-point for the activation of RVI clearly lies below 327 mosmol/l. Na+/H+ antiport is the most sensitive Na+ importer involved in RVI, whereas Na+ conductance plays the prominent role from 360 mosmol/l upwards.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2013
    Keywords: HCO3 secretion ; Membrane potentials ; Cell membrane ion permeabilities ; Ouabain ; Prostaglandin E1 ; Loperamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Loperamide inhibits PGE1-induced electrogenic HCO3 secretion in guinea-pig gallbladder. Underlying changes in epithelial cell membrane properties were investgated using intracellular microelectrode techniques in vitro. In the absence of PGE1, mucosal loperamide (10−4 mol/l) reversibly depolarized both cell membranes by ∼ 6 mV. The apparent ratio of membrane resistances (R a/R b) remained unchanged and so did voltage responses to luminal Cl removal and Na reduction. The depolarizing response to elevation of luminal K concentration from 5 to 76 mmol/l was decreased from 13 to 8 mV. In the presence of 1 PGE1, the apical membrane is mainly permeable to Cl and HCO3. Under these conditions, loperamide reduced membrane potentials by ∼ 10 mV,R a/R b remaining constant at ∼ 0.4. Effects on voltage responses to changes in luminal Na or K concentration were unchanged. Responses to luminal Cl removal (transient depolarization) were greatly enhanced (from 22 to 42 mV) as predictable from the fall in K permeability that hinders Cl efflux from cell into lumen. Less marked but significant effects were obtained with 10−5 mol/l (mucosal side) and serosal loperamide (10−4 mol/l). We suggest that loperamide inhibits electrogenic HCO3 secretion by reducing apical membrane K permeability. The resulting depolarization diminishes the driving force for conductive anion efflux from cell into lumen. This conclusion is supported by the ability of luminal K elevation to mimick loperamide inhibition of the secretory flux of HCO3 (pH-stat experiments).
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2013
    Keywords: Rat hepatocytes ; Electrophysiology ; Membrane potentials ; Na+ conductance ; Bile acids ; Taurocholic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rat hepatocytes in primary culture were impaled with conventional microelectrodes. Addition of 5–100 μmol/l taurocholate led to a slowly developing depolarization that was maximal at 50 μmol/l (10.5±1.5 mV, n=15) and not reversible. The effect was Na+ dependent and decreased in cells preincubated with 1 μmol/l taurocholate. Increasing external K+ tenfold depolarized the cells by 12.3±2.3 mV under control conditions and by 6.3±1.2 mV with 50 μmol/l taurocholate present (n=7). Depolarization by 1 mmol/l Ba2+ was 7.6±0.8 mV and 6.0±0.7 mV (n=9) before and after addition of taurocholate, respectively. Cable analysis and Na+ substitution experiments reveal that this apparent decrease in K+ conductance reflects an actual increase in Na+ conductance: in the presence of taurocholate, specific cell membrane resistance decreased from 2.8 to 2.3 kΩ · cm2 · Na+ substitution by 95% depolarized cell membranes by 8.9±2.9 mV (n=9), probably due to indirect effects on K+ conductance via changes in cell pH. With taurocholate present, the same manoeuvre changed membrane voltages by −0.8±2.6 mV. When Na+ concentration was restored to 100% from solutions containing 5% Na+, cells hyperpolarized by 3.5±3.6 mV (n=7) under control conditions and depolarized by 4.4±2.9 mV in the presence of taurocholate, respectively. In Cl− substitution experiments, there was no evidence for changes in Cl− conductance by taurocholate. These results show that taurocholate-induced membrane depolarization is due to an increase in Na+ conductance probably via uptake of the bile acid.
    Type of Medium: Electronic Resource
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  • 6
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    In:  (Diploma thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 68 pp
    Publication Date: 2013-05-22
    Type: Thesis , NonPeerReviewed
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  • 7
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    In:  (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 68 pp
    Publication Date: 2021-04-27
    Type: Thesis , NonPeerReviewed
    Format: text
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  • 8
    Publication Date: 2021-04-29
    Type: Dataset
    Format: text/tab-separated-values, 129364 data points
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  • 9
    Publication Date: 2021-04-29
    Type: Dataset
    Format: text/tab-separated-values, 188944 data points
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