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  • American Physiological Society  (59)
  • 1
    Online Resource
    Online Resource
    American Physiological Society ; 2004
    In:  American Journal of Physiology-Renal Physiology Vol. 286, No. 6 ( 2004-06), p. F1046-F1053
    In: American Journal of Physiology-Renal Physiology, American Physiological Society, Vol. 286, No. 6 ( 2004-06), p. F1046-F1053
    Abstract: Osmotic shock by addition of sucrose to the medium stimulates erythrocyte sphingomyelinase with subsequent ceramide formation and triggers Ca 2+ entry through stimulation of cation channels. Both ceramide and Ca 2+ activate an erythrocyte scramblase, leading to breakdown of phosphatidylserine asymmetry, a typical feature of apoptosis. Because erythrocytes are regularly exposed to osmotic shock during passage of kidney medulla, the present study explored the influence of NaCl and urea on erythrocyte phosphatidylserine exposure as determined by annexin binding. The percentage of annexin-binding erythrocytes increased from 〈 5 to 80 ± 4% ( n = 4) upon addition of 650 mM sucrose, an effect paralleled by activation of the cation channel and stimulation of ceramide formation. The number of annexin-binding erythrocytes increased only to 18% after addition of 325 mM NaCl and was not increased by addition of 650 mM urea. According to whole cell patch-clamp experiments, the cation conductance was activated by replacement of extracellular Cl − with gluconate at isotonic conditions or by addition of hypertonic sucrose or urea. Although stimulating the cation conductance, urea abrogated the annexin binding and concomitant increase of ceramide levels induced by osmotic cell shrinkage. In vitro sphingomyelinase assays demonstrated a direct inhibitory effect of urea on sphingomyelinase activity. Urea did not significantly interfere with annexin binding after addition of ceramide. In conclusion, both Cl − and urea blunt erythrocyte phosphatidylserine exposure after osmotic shock. Whereas Cl − is effective through inhibition of the cation conductance, urea exerts its effect through inhibition of sphingomyelinase, thus blunting formation of ceramide.
    Type of Medium: Online Resource
    ISSN: 1931-857X , 1522-1466
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2004
    detail.hit.zdb_id: 1477287-5
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  • 2
    Online Resource
    Online Resource
    American Physiological Society ; 2005
    In:  American Journal of Physiology-Cell Physiology Vol. 288, No. 2 ( 2005-02), p. C396-C402
    In: American Journal of Physiology-Cell Physiology, American Physiological Society, Vol. 288, No. 2 ( 2005-02), p. C396-C402
    Abstract: Pb + intoxication causes anemia that is partially due to a decreased life span of circulating erythrocytes. As shown recently, a Ca 2+ -sensitive erythrocyte scramblase is activated by osmotic shock, oxidative stress, and/or energy depletion, leading to exposure of phosphatidylserine at the erythrocyte surface. Because macrophages are equipped with phosphatidylserine receptors, they bind, engulf, and degrade phosphatidylserine-exposing cells. The present experiments were performed to explore whether Pb + ions trigger phosphatidylserine exposure of erythrocytes. The phosphatidylserine exposure was estimated on the basis of annexin binding as determined using fluorescence-activated cell sorting (FACS) analysis. Exposure to Pb + ions [≥0.1 μM Pb(NO 3 ) 2 ] significantly increased annexin binding. This effect was paralleled by erythrocyte shrinkage, which was apparent on the basis of the decrease in forward scatter in FACS analysis. The effect of Pb + ions on cell volume was virtually abolished, and the effect of Pb + ions on annexin binding was blunted after increase of extracellular K + concentration. Moreover, both effects of Pb + ions were partially prevented in the presence of clotrimazole (10 μM), an inhibitor of the Ca 2+ -sensitive K + channels in the erythrocyte cell membrane. Whole cell patch-clamp experiments disclosed a significant activation of a K + -selective conductance after Pb + ion exposure, an effect requiring higher (10 μM) concentrations, however. In conclusion, Pb + ions activate erythrocyte K + channels, leading to erythrocyte shrinkage, and also activate the erythrocyte scramblase, leading to phosphatidylserine exposure. The effect could well contribute to the reported decreased life span of circulating erythrocytes during Pb + intoxication.
    Type of Medium: Online Resource
    ISSN: 0363-6143 , 1522-1563
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2005
    detail.hit.zdb_id: 1477334-X
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  • 3
    Online Resource
    Online Resource
    American Physiological Society ; 2003
    In:  American Journal of Physiology-Cell Physiology Vol. 285, No. 6 ( 2003-12), p. C1553-C1560
    In: American Journal of Physiology-Cell Physiology, American Physiological Society, Vol. 285, No. 6 ( 2003-12), p. C1553-C1560
    Abstract: Exposure of erythrocytes to the Ca 2+ ionophore ionomycin has recently been shown to induce cell shrinkage, cell membrane blebbing, and breakdown of phosphatidylserine asymmetry, all features typical of apoptosis of nucleated cells. Although breakdown of phosphatidylserine asymmetry is thought to result from activation of a Ca 2+ -sensitive scramblase, the mechanism and role of cell shrinkage have not been explored. The present study was performed to test whether ionomycin-induced activation of Ca 2+ -sensitive Gardos K + channels and subsequent cell shrinkage participate in ionomycin-induced breakdown of phosphatidylserine asymmetry of human erythrocytes. According to on-cell patch-clamp experiments, ionomycin (1 μM) induces activation of inwardly rectifying K + -selective channels in the erythrocyte membrane. Fluorescence-activated cell sorter analysis reveals that ionomycin leads to a significant decrease of forward scatter, reflecting cell volume, an effect blunted by an increase of extracellular K + concentration to 25 mM and exposure to the Gardos K + channel blockers charybdotoxin (230 nM) and clotrimazole (5 μM). As reflected by annexin binding, breakdown of phosphatidylserine asymmetry is triggered by ionomycin, an effect again blunted, but not abolished, by an increase of extracellular K + concentration and exposure to charybdotoxin (230 nM) and clotrimazole (5 μM). Similar to ionomycin, glucose depletion leads (within 55 h) to annexin binding of erythrocytes, an effect again partially reversed by an increase of extracellular K + concentration and exposure to charybdotoxin. K-562 human erythroleukemia cells similarly respond to ionomycin with cell shrinkage and annexin binding, effects blunted by antisense, but not sense, oligonucleotides against the small-conductance Ca 2+ -activated K + channel isoform hSK4 (KCNN4). The experiments disclose a novel functional role of Ca 2+ -sensitive K + channels in erythrocytes, i.e., their participation in regulation of erythrocyte apoptosis.
    Type of Medium: Online Resource
    ISSN: 0363-6143 , 1522-1563
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2003
    detail.hit.zdb_id: 1477334-X
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  • 4
    In: American Journal of Physiology-Cell Physiology, American Physiological Society, Vol. 291, No. 4 ( 2006-10), p. C710-C717
    Abstract: Eryptosis or apoptosis-like death of erythrocytes is characterized by phosphatidylserine exposure and erythrocyte shrinkage, both typical features of nucleated apoptotic cells. Eryptosis is triggered by activation of nonselective Ca 2+ -permeable cation channels with subsequent entry of Ca 2+ and stimulation of Ca 2+ -sensitive scrambling of the cell membrane. The channels are activated and thus eryptosis is triggered by Cl − removal, osmotic shock, oxidative stress, or glucose deprivation. The present study has been performed to compare cation channel activity and susceptibility to eryptosis in neonatal and adult erythrocytes. Channel activity was determined by patch-clamp analysis, cytosolic Ca 2+ activity by fluo-3 fluorescence, phosphatidylserine exposure by FITC-labeled annexin V binding, and cell shrinkage by decrease in forward scatter in fluorescence-activated cell sorting analysis. Prostaglandin E 2 (PGE 2 ) formation, cation channel activity, Ca 2+ entry, annexin V binding, and decreased forward scatter were triggered by removal of Cl − in both adult and neonatal erythrocytes. The effects were, however, significantly blunted in neonatal erythrocytes. Osmotic shock, PGE 2, and platelet-activating factor similarly increased annexin V binding and decreased forward scatter, effects again significantly reduced in neonatal erythrocytes. On the other hand, spontaneous and oxidative (addition of tert-butylperoxide) stress-induced eryptosis was significantly larger in neonatal erythrocytes. In conclusion, cation channel activity, Ca 2+ leakage, and thus channel-dependent triggering of eryptosis are blunted, whereas spontaneous and oxidative stress-induced eryptosis is more pronounced in neonatal erythrocytes.
    Type of Medium: Online Resource
    ISSN: 0363-6143 , 1522-1563
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2006
    detail.hit.zdb_id: 1477334-X
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  • 5
    Online Resource
    Online Resource
    American Physiological Society ; 2010
    In:  American Journal of Physiology-Renal Physiology Vol. 298, No. 5 ( 2010-05), p. F1113-F1117
    In: American Journal of Physiology-Renal Physiology, American Physiological Society, Vol. 298, No. 5 ( 2010-05), p. F1113-F1117
    Abstract: Akt/PKB is known to regulate the facilitative glucose carrier GLUT4. Nothing is known, however, of the role of Akt/PKB in the regulation of renal epithelial transport. To explore whether Akt2/PKBβ influences the Na + -coupled glucose cotransporter SGLT1, human SGLT1 was expressed in Xenopus laevis oocytes with or without Akt/PKB, and electrogenic glucose transport was determined by dual-electrode voltage clamp. The coexpression of Akt/PKB in SGLT1-expressing oocytes was followed by an increase in glucose-induced currents. To study the functional significance of Akt/PKB-sensitive renal glucose transport, further experiments were performed in gene-targeted mice lacking functional Akt2/PKBβ ( akt2 −/− ) and in their wild-type littermates ( akt2 +/+ ). Plasma glucose concentration was significantly higher in akt2 −/− mice than in akt2 +/+ mice but was virtually identical to the plasma glucose concentration in fructose-treated akt2 +/+ mice. Urinary glucose excretion was significantly higher in akt2 −/− mice compared with akt2 +/+ mice with or without fructose treatment. Moreover, the glucose-induced depolarization of proximal tubular cells was significantly smaller in isolated, perfused renal tubules from akt2 −/− mice than in those from akt2 +/+ mice. In conclusion, Akt2/PKBβ plays a role in the regulation of renal glucose transport.
    Type of Medium: Online Resource
    ISSN: 1931-857X , 1522-1466
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2010
    detail.hit.zdb_id: 1477287-5
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  • 6
    Online Resource
    Online Resource
    American Physiological Society ; 2005
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 289, No. 2 ( 2005-08), p. R395-R401
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 289, No. 2 ( 2005-08), p. R395-R401
    Abstract: Mineralocorticoids modify salt balance by both stimulating salt intake and inhibiting salt loss. Renal salt retention is accomplished by upregulation of reabsorption, an effect partially mediated by serum- and glucocorticoid-inducible kinase 1 (SGK1). The present study explored the contribution of SGK1 to the regulation of renal function, salt intake, and blood pressure during mineralocorticoid excess. DOCA/1% NaCl treatment increased blood pressure and creatinine clearance to a similar extent in SGK1-deficient sgk1 −/− and wild-type sgk1 +/+ mice but led to more pronounced increase of proteinuria in sgk1 +/+ mice (by 474 ± 89%) than in sgk1 −/− mice (by 154 ± 31%). DOCA/1% NaCl treatment led to significant increase of kidney weight (by 24%) and to hypokalemia (from 3.9 ± 0.1 to 2.7 ± 0.1 mmol/l) only in sgk1 +/+ mice. The treatment enhanced renal Na + excretion significantly more in sgk1 +/+ mice (from 3 ± 1 to 134 ± 32 μmol·24 h −1 ·g body wt −1 ) than in sgk1 −/− mice (from 4 ± 1 to 49 ± 8 μmol·24 h −1 ·g body wt −1 ), pointing to SGK1-dependent stimulation of salt intake. With access to two drinking bottles containing 1% NaCl or water, DOCA treatment did not significantly affect water intake in either genotype but increased 1% NaCl intake in sgk1 +/+ mice (within 9 days from 3.5 ± 0.9 to 16.5 ± 2.4 ml/day) consistent with DOCA-induced salt appetite. This response was significantly attenuated in sgk1 −/− mice (from 2.6 ± 0.6 to 5.9 ± 0.9 ml/day). Thus SGK1 contributes to the stimulation of salt intake, kidney growth, proteinuria, and renal K + excretion during mineralocorticoid excess.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2005
    detail.hit.zdb_id: 1477297-8
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  • 7
    Online Resource
    Online Resource
    American Physiological Society ; 2006
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 291, No. 5 ( 2006-11), p. R1533-R1538
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 291, No. 5 ( 2006-11), p. R1533-R1538
    Abstract: The phosphoinositide-dependent kinase-1 (PDK-1) activates the serum- and glucocorticoid-inducible kinase and protein kinase B isoforms, which, in turn, are known to stimulate the renal and intestinal Na + -dependent glucose transporter 1. The present study has been performed to explore the role of PDK-1 in electrogenic glucose transport in small intestine and proximal renal tubules. To this end, mice expressing ∼20% of PDK-1 ( pdk1 hm ) were compared with their wild-type littermates ( pdk1 wt ). According to Ussing chamber experiments, electrogenic glucose transport was significantly smaller in the jejunum of pdk1 hm than of pdk1 wt mice. Similarly, proximal tubular electrogenic glucose transport in isolated, perfused renal tubule segments was decreased in pdk1 hm compared with pdk1 wt mice. Intraperitoneal injection of 3 g/kg body wt glucose resulted in a similar increase of plasma glucose concentration in pdk1 hm and in pdk1 wt mice but led to a higher increase of urinary glucose excretion in pdk1 hm mice. In conclusion, reduction of functional PDK-1 leads to impairment of electrogenic intestinal glucose absorption and renal glucose reabsorption. The experiments disclose a novel element of glucose transport regulation in kidney and small intestine.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2006
    detail.hit.zdb_id: 1477297-8
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  • 8
    Online Resource
    Online Resource
    American Physiological Society ; 2006
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 290, No. 4 ( 2006-04), p. R945-R950
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 290, No. 4 ( 2006-04), p. R945-R950
    Abstract: Serum- and glucocorticoid-inducible kinase (SGK) 1 and SGK3 share the ability to upregulate several ion channels, including the epithelial Na + channel. Whereas SGK1 is under genomic control of mineralocorticoids and glucocorticoids, SGK3 is constitutively expressed. The SKG1-knockout ( sgk1 −/− ) mouse is seemingly normal when it is fed a standard diet, but its ability to retain NaCl is impaired when it is fed a salt-deficient diet. In the SGK3-knockout ( sgk3 −/− ) mouse fed standard and salt-deficient diets, hair growth is strikingly delayed but NaCl excretion is normal. Thus the possibility was considered that SGK1 and SGK3 could mutually replace each other, thus preventing severe NaCl loss in sgk1 −/− and sgk3 −/− mice. We crossed SGK1- and SGK3-knockout mice and compared renal electrolyte excretion of the double mutants ( sgk1 −/− / sgk3 −/− ) with that of their wild-type littermates ( sgk1 +/+ / sgk3 +/+ ). Similar to sgk3 −/− mice, the sgk1 −/− / sgk3 −/− mice display delayed hair growth. Blood pressure was slightly, but significantly ( P 〈 0.03), lower in sgk1 −/− / sgk3 −/− (102 ± 4 mmHg) than in sgk1 +/+ / sgk3 +/+ (114 ± 3 mmHg) mice, a difference that was maintained in mice fed low- and high-salt diets. Plasma aldosterone concentrations were significantly ( P 〈 0.01) higher in sgk1 −/− / sgk3 −/− than in sgk1 +/+ sgk3 +/+ mice fed control (511 ± 143 vs. 143 ± 32 pg/ml) and low-salt (1,325 ± 199 vs. 362 ± 145 pg/ml) diets. During salt depletion, absolute and fractional excretions of Na + were significantly ( P 〈 0.01) higher in sgk1 −/− / sgk3 −/− (1.2 ± 0.2 μmol/24 h g body wt, 0.12 ± 0.03%) than in sgk1 +/+ / sgk3 +/+ (0.4 ± 0.1 μmol/24 h g body wt, 0.04 ± 0.01%) mice. The sgk1 −/− / sgk3 −/− mice share the delayed hair growth with sgk3 −/− mice and the modestly impaired renal salt retention with sgk1 −/− mice. Additional lack of the isoform kinase does not substantially compound the phenotype for either property.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2006
    detail.hit.zdb_id: 1477297-8
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  • 9
    Online Resource
    Online Resource
    American Physiological Society ; 2006
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 291, No. 5 ( 2006-11), p. G868-G876
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 291, No. 5 ( 2006-11), p. G868-G876
    Abstract: In vitro experiments have demonstrated the stimulating effect of serum- and glucocorticoid-inducible kinase (SGK)1 on the activity of the Na + /H + exchanger (NHE3). SGK1 requires activation by phosphoinositide-dependent kinase (PDK)1, which may thus similarly play a role in the regulation of NHE3-dependent epithelial electrolyte transport. The present study was performed to explore the role of PDK1 in the regulation of NHE3 activity. Because mice completely lacking functional PDK1 are not viable, hypomorphic mice expressing ∼20% of PDK1 ( pdk1 hm ) were compared with their wild-type littermates ( pdk1 wt ). NHE3 activity in the intestine and PDK1-overexpressing HEK-293 cells was estimated by utilizing 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence for the determination of intracellular pH. NHE activity was reflected by the Na + -dependent pH recovery from an ammonium prepulse (ΔpH NHE ). The pH changes after an ammonium pulse allowed the calculation of cellular buffer capacity, which was not significantly different between pdk1 hm and pdk1 wt mice. ΔpH NHE was in pdk1 hm mice, only 30 ± 6% of the value obtained in pdk1 wt mice. Conversely, ΔpH NHE was 32 ± 7% larger in PDK1-overexpressing HEK-293 cells than in HEK-293 cells expressing the empty vector. The difference between pdk1 hm and pdk1 wt mice and between PDK1-overexpressing and empty vector-transfected HEK cells, respectively, was completely abolished in the presence of the NHE3 inhibitor S3226 (10 μM). In conclusion, defective PDK1 expression leads to significant impairment of NHE3 activity in the intestine, pointing to a role of PDK1-dependent signaling in the regulation of NHE-mediated electrolyte transport.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2006
    detail.hit.zdb_id: 1477329-6
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  • 10
    Online Resource
    Online Resource
    American Physiological Society ; 2011
    In:  American Journal of Physiology-Cell Physiology Vol. 301, No. 2 ( 2011-08), p. C490-C498
    In: American Journal of Physiology-Cell Physiology, American Physiological Society, Vol. 301, No. 2 ( 2011-08), p. C490-C498
    Abstract: Blebbistatin, a myosin II inhibitor, interferes with myosin-actin interaction and microtubule assembly. By influencing cytoskeletal dynamics blebbistatin counteracts apoptosis of several types of nucleated cells. Even though lacking nuclei and mitochondria, erythrocytes may undergo suicidal cell death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Triggers of eryptosis include energy depletion and osmotic shock, which enhance cytosolic Ca 2+ activity with subsequent Ca 2+ -sensitive cell shrinkage and cell membrane scrambling. The present study explored the effect of blebbistatin on eryptosis. Cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, cell volume from forward scatter in fluorescence-activated cell sorting analysis and cytosolic Ca 2+ concentration from Fluo3 fluorescence. Exposure to blebbistatin on its own (1–50 μM) did not significantly modify cytosolic Ca 2+ concentration, forward scatter, or annexin V binding. Glucose depletion (48 h) was followed by a significant increase of Fluo3 fluorescence and annexin V binding, effects significantly blunted by blebbistatin (Fluo3 fluorescence ≥ 25 μM, annexin V binding ≥ 10 μM). Osmotic shock (addition of 550 mM sucrose) again significantly increased Fluo3 fluorescence and annexin binding, effects again significantly blunted by blebbistatin (Fluo3 fluorescence ≥ 25 μM, annexin V binding ≥ 25 μM). The present observations disclose a novel effect of blebbistatin, i.e., an influence on Ca 2+ entry and suicidal erythrocyte death following energy depletion and osmotic shock.
    Type of Medium: Online Resource
    ISSN: 0363-6143 , 1522-1563
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2011
    detail.hit.zdb_id: 1477334-X
    SSG: 12
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