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Joachim W Deitmer - One of the best experts on this subject based on the ideXlab platform.

  • Functional expression of electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse cortical astrocytes is dependent on S255-257 and regulated by mTOR.
    Glia, 2019
    Co-Authors: Shokoufeh Khakipoor, Shefeeq M Theparambil, Joachim W Deitmer, Marina Giannaki, Jana Zecha, Bernhard Kuster, Stephan Heermann, Eleni Roussa
    Abstract:

    The electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), is the major bicarbonate transporter expressed in astrocytes. It is highly sensitive for bicarbonate and the main regulator of intracellular, extracellular, and synaptic pH, thereby modulating neuronal excitability. However, despite these essential functions, the molecular mechanisms underlying NBCe1-mediated astrocytic response to extracellular pH changes are mostly unknown. Using primary mouse cortical astrocyte cultures, we investigated the effect of long-term extracellular metabolic Alkalosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant downregulation of NBCe1 activity following metabolic Alkalosis without influencing protein abundance or surface expression of NBCe1. During Alkalosis, the rate of intracellular H+ changes upon challenging NBCe1 was decreased in wild-type astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Alkalosis-induced decrease of NBCe1 activity was rescued after activation of mTOR signaling. Moreover, mass spectrometry revealed constitutively phosphorylated S255-257 and mutational analysis uncovered these residues being crucial for NBCe1 transport activity. Our results demonstrate a novel mTOR-regulated mechanism by which NBCe1 functional expression is regulated. Such mechanism likely applies not only for NBCe1 in astrocytes, but in epithelial cells as well.

  • reversed electrogenic sodium bicarbonate cotransporter 1 is the major acid loader during recovery from cytosolic Alkalosis in mouse cortical astrocytes
    The Journal of Physiology, 2015
    Co-Authors: Shefeeq M Theparambil, Zinnia Naoshin, Anne Thyssen, Joachim W Deitmer
    Abstract:

    KEY POINTS The regulation of H(+) i from cytosolic Alkalosis has generally been attributed to the activity of Cl(-) -coupled acid loaders/base extruders in most cell types, including brain cells. The present study demonstrates that outwardly-directed sodium bicarbonate cotransport via electrogenic sodium bicarbonate cotransporter 1 (NBCe1) mediates the major fraction of H(+) i regulation from cytosolic Alkalosis in mouse cortical astrocytes. Cl(-) -coupled acid-loading transporters play only a minor role in the regulation of H(+) i from Alkalosis in mouse cortical astrocytes. NBCe1-mediated H(+) i regulation from Alkalosis was dominant, with the support of intracellular carbonic anhydrase II, even when the intra- and extracellular [HCO3 (-) ] was very low (<1mM), as in nominally CO2 /HCO3 (-) free condition. A reversed NBCe1 in astrocytes may also be significant for stabilizing extracellular pH in brain tissue. ABSTRACT Recovery of intracellular pH from cytosolic Alkalosis has been attributed primarily to Cl(-) coupled acid loaders/base extruders such as Cl(-) /HCO3 (-) or Cl(-) /OH(-) exchangers. We have studied this process in cortical astrocytes from wild-type and transgenic mouse models with gene deletion for the electrogenic sodium bicarbonate cotransporter 1 (NBCe1) and for carbonic anhydrase (CA) isoform II. An acute cytosolic Alkalosis was induced by the removal of either CO2 /HCO3 (-) or butyric acid, and the subsequent acid loading was analysed by monitoring changes in cytosolic H(+) or Na(+) using ion-sensitive fluorescent dyes. We have identified that NBCe1 reverses during Alkalosis and contributes more than 70% to the rate of recovery from Alkalosis by extruding Na(+) and HCO3 (-) . After CA inhibition or in CAII-knockout (KO) cells, the rate of recovery was reduced by 40%, and even by 70% in the nominal absence of CO2 /HCO3 (-) . Increasing the extracellular K(+) concentration modulated the rate of acid loading in wild-type cells, but not in NBCe1-KO cells. Removing chloride had only a minor effect on the recovery from Alkalosis. Reversal of NBCe1 by reducing pH/[HCO3 (-) ] was demonstrated in astrocytes and in Xenopus oocytes, in which human NBCe1 was heterologously expressed. The results obtained suggest that reversed NBCe1, supported by CAII activity, plays a major role in acid-loading cortical astrocytes to support recovery from cytosolic Alkalosis.

Shefeeq M Theparambil - One of the best experts on this subject based on the ideXlab platform.

  • Functional expression of electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse cortical astrocytes is dependent on S255-257 and regulated by mTOR.
    Glia, 2019
    Co-Authors: Shokoufeh Khakipoor, Shefeeq M Theparambil, Joachim W Deitmer, Marina Giannaki, Jana Zecha, Bernhard Kuster, Stephan Heermann, Eleni Roussa
    Abstract:

    The electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), is the major bicarbonate transporter expressed in astrocytes. It is highly sensitive for bicarbonate and the main regulator of intracellular, extracellular, and synaptic pH, thereby modulating neuronal excitability. However, despite these essential functions, the molecular mechanisms underlying NBCe1-mediated astrocytic response to extracellular pH changes are mostly unknown. Using primary mouse cortical astrocyte cultures, we investigated the effect of long-term extracellular metabolic Alkalosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant downregulation of NBCe1 activity following metabolic Alkalosis without influencing protein abundance or surface expression of NBCe1. During Alkalosis, the rate of intracellular H+ changes upon challenging NBCe1 was decreased in wild-type astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Alkalosis-induced decrease of NBCe1 activity was rescued after activation of mTOR signaling. Moreover, mass spectrometry revealed constitutively phosphorylated S255-257 and mutational analysis uncovered these residues being crucial for NBCe1 transport activity. Our results demonstrate a novel mTOR-regulated mechanism by which NBCe1 functional expression is regulated. Such mechanism likely applies not only for NBCe1 in astrocytes, but in epithelial cells as well.

  • reversed electrogenic sodium bicarbonate cotransporter 1 is the major acid loader during recovery from cytosolic Alkalosis in mouse cortical astrocytes
    The Journal of Physiology, 2015
    Co-Authors: Shefeeq M Theparambil, Zinnia Naoshin, Anne Thyssen, Joachim W Deitmer
    Abstract:

    KEY POINTS The regulation of H(+) i from cytosolic Alkalosis has generally been attributed to the activity of Cl(-) -coupled acid loaders/base extruders in most cell types, including brain cells. The present study demonstrates that outwardly-directed sodium bicarbonate cotransport via electrogenic sodium bicarbonate cotransporter 1 (NBCe1) mediates the major fraction of H(+) i regulation from cytosolic Alkalosis in mouse cortical astrocytes. Cl(-) -coupled acid-loading transporters play only a minor role in the regulation of H(+) i from Alkalosis in mouse cortical astrocytes. NBCe1-mediated H(+) i regulation from Alkalosis was dominant, with the support of intracellular carbonic anhydrase II, even when the intra- and extracellular [HCO3 (-) ] was very low (<1mM), as in nominally CO2 /HCO3 (-) free condition. A reversed NBCe1 in astrocytes may also be significant for stabilizing extracellular pH in brain tissue. ABSTRACT Recovery of intracellular pH from cytosolic Alkalosis has been attributed primarily to Cl(-) coupled acid loaders/base extruders such as Cl(-) /HCO3 (-) or Cl(-) /OH(-) exchangers. We have studied this process in cortical astrocytes from wild-type and transgenic mouse models with gene deletion for the electrogenic sodium bicarbonate cotransporter 1 (NBCe1) and for carbonic anhydrase (CA) isoform II. An acute cytosolic Alkalosis was induced by the removal of either CO2 /HCO3 (-) or butyric acid, and the subsequent acid loading was analysed by monitoring changes in cytosolic H(+) or Na(+) using ion-sensitive fluorescent dyes. We have identified that NBCe1 reverses during Alkalosis and contributes more than 70% to the rate of recovery from Alkalosis by extruding Na(+) and HCO3 (-) . After CA inhibition or in CAII-knockout (KO) cells, the rate of recovery was reduced by 40%, and even by 70% in the nominal absence of CO2 /HCO3 (-) . Increasing the extracellular K(+) concentration modulated the rate of acid loading in wild-type cells, but not in NBCe1-KO cells. Removing chloride had only a minor effect on the recovery from Alkalosis. Reversal of NBCe1 by reducing pH/[HCO3 (-) ] was demonstrated in astrocytes and in Xenopus oocytes, in which human NBCe1 was heterologously expressed. The results obtained suggest that reversed NBCe1, supported by CAII activity, plays a major role in acid-loading cortical astrocytes to support recovery from cytosolic Alkalosis.

Eleni Roussa - One of the best experts on this subject based on the ideXlab platform.

  • Functional expression of electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse cortical astrocytes is dependent on S255-257 and regulated by mTOR.
    Glia, 2019
    Co-Authors: Shokoufeh Khakipoor, Shefeeq M Theparambil, Joachim W Deitmer, Marina Giannaki, Jana Zecha, Bernhard Kuster, Stephan Heermann, Eleni Roussa
    Abstract:

    The electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), is the major bicarbonate transporter expressed in astrocytes. It is highly sensitive for bicarbonate and the main regulator of intracellular, extracellular, and synaptic pH, thereby modulating neuronal excitability. However, despite these essential functions, the molecular mechanisms underlying NBCe1-mediated astrocytic response to extracellular pH changes are mostly unknown. Using primary mouse cortical astrocyte cultures, we investigated the effect of long-term extracellular metabolic Alkalosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant downregulation of NBCe1 activity following metabolic Alkalosis without influencing protein abundance or surface expression of NBCe1. During Alkalosis, the rate of intracellular H+ changes upon challenging NBCe1 was decreased in wild-type astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Alkalosis-induced decrease of NBCe1 activity was rescued after activation of mTOR signaling. Moreover, mass spectrometry revealed constitutively phosphorylated S255-257 and mutational analysis uncovered these residues being crucial for NBCe1 transport activity. Our results demonstrate a novel mTOR-regulated mechanism by which NBCe1 functional expression is regulated. Such mechanism likely applies not only for NBCe1 in astrocytes, but in epithelial cells as well.

Shokoufeh Khakipoor - One of the best experts on this subject based on the ideXlab platform.

  • Functional expression of electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse cortical astrocytes is dependent on S255-257 and regulated by mTOR.
    Glia, 2019
    Co-Authors: Shokoufeh Khakipoor, Shefeeq M Theparambil, Joachim W Deitmer, Marina Giannaki, Jana Zecha, Bernhard Kuster, Stephan Heermann, Eleni Roussa
    Abstract:

    The electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), is the major bicarbonate transporter expressed in astrocytes. It is highly sensitive for bicarbonate and the main regulator of intracellular, extracellular, and synaptic pH, thereby modulating neuronal excitability. However, despite these essential functions, the molecular mechanisms underlying NBCe1-mediated astrocytic response to extracellular pH changes are mostly unknown. Using primary mouse cortical astrocyte cultures, we investigated the effect of long-term extracellular metabolic Alkalosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant downregulation of NBCe1 activity following metabolic Alkalosis without influencing protein abundance or surface expression of NBCe1. During Alkalosis, the rate of intracellular H+ changes upon challenging NBCe1 was decreased in wild-type astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Alkalosis-induced decrease of NBCe1 activity was rescued after activation of mTOR signaling. Moreover, mass spectrometry revealed constitutively phosphorylated S255-257 and mutational analysis uncovered these residues being crucial for NBCe1 transport activity. Our results demonstrate a novel mTOR-regulated mechanism by which NBCe1 functional expression is regulated. Such mechanism likely applies not only for NBCe1 in astrocytes, but in epithelial cells as well.

John F Gennari - One of the best experts on this subject based on the ideXlab platform.

  • pathophysiology of metabolic Alkalosis a new classification based on the centrality of stimulated collecting duct ion transport
    American Journal of Kidney Diseases, 2011
    Co-Authors: John F Gennari
    Abstract:

    Metabolic Alkalosis is a unique acid-base disorder because it can be induced and sustained by functional alterations in renal ion transport. This review summarizes more than 50 years of research into the pathophysiologic processes causing this disorder. The evidence reviewed supports the hypothesis that virtually all forms of metabolic Alkalosis are sustained by enhanced collecting duct hydrogen ion secretion, induced by stimulation of sodium uptake through the epithelial sodium channel (ENaC). Enhanced collecting duct hydrogen ion secretion in metabolic Alkalosis occurs most commonly secondary to changes in ion transport earlier along the nephron, but also can occur as the result of primary stimulation of ENaC. In both these settings, potassium secretion is stimulated, and abnormal potassium losses cause depletion of body potassium stores. Potassium depletion has a key role in sustaining metabolic Alkalosis by stimulating renal hydrogen ion secretion, enhancing renal ammonium production and excretion, and downregulating sodium reabsorption in the loop of Henle and early distal tubule. A new classification of the causes of metabolic Alkalosis is proposed based on these pathophysiologic events rather than response to treatment.

  • severe metabolic Alkalosis in a hemodialysis patient
    American Journal of Kidney Diseases, 2011
    Co-Authors: Lu Huber, John F Gennari
    Abstract:

    We present a patient with end-stage kidney disease receiving hemodialysis therapy who developed severe metabolic Alkalosis secondary to vomiting. This case illustrates the important differences in pathogenesis, diagnosis, and management of this common acid-base disorder in patients without kidney function. The diagnostic approach and management strategy for metabolic Alkalosis are discussed, highlighting the special issues to be considered in dialysis patients.