Role of Na/K/Cl cotransport in astrocytes

1992 ◽  
Vol 70 (S1) ◽  
pp. S260-S262 ◽  
Author(s):  
Wolfgang Walz
Keyword(s):  
Volume Regulation ◽  
Ion Homeostasis ◽  
Combined Cycle ◽  
Kinetic Characterization ◽  
Cultured Astrocytes ◽  
Net Uptake ◽  
Swelling Volume ◽  
External K

The kinetic characterization of the Na/K/Cl cotransport of cultured astrocytes and evidence for its involvement in volume regulation and K+ net uptake during K+ clearance are reviewed. Emphasis is put on experimental evidence for a proposed sodium cycle in astrocytes; this cycle involves a Na+–K+ ATPase that is stimulated by both a high external K+ and intracellular Na+. Elevated external K+ also stimulates the Na/K/Cl carrier, transporting these ions inward. As a result Na+ is cycled across the membrane, carried inward by the Na/K/Cl carrier, and returned by the Na+–K+ ATPase. Both functionally coupled mechanisms lead to intracellular KCl accumulation and inward movements of water to compensate for increased osmolarity. The combined cycle is expected to play a major role in the regulation of physiological K+ levels in the brain.Key words: furosemide, ion homeostasis, Na+–K+ ATPase, swelling, volume regulation.

Swelling and potassium uptake in cultured astrocytes

1987 ◽  
Vol 65 (5) ◽  
pp. 1051-1057 ◽  
Author(s):  
Wolfgang Walz
Keyword(s):  
Energy Source ◽  
Driving Force ◽  
Primary Cultures ◽  
Volume Changes ◽  
Cultured Astrocytes ◽  
High K ◽  
Ion Activity ◽  
Net Uptake ◽  
Two Phases ◽  
External K

The intracellular water content of astrocytes in primary cultures shows a biphasic swelling pattern on exposure to various increased external K+ concentrations over the range of 1.5–100 mM. The two phases (physiological, 1.5–12 mM K+; pathological, 25–100 mM K+) are based on two different mechanisms. Both can be blocked by low Cl− solutions and involve intensive net uptake of K+. However, the physiological phase consists of the activation of a KCl + NaCl carrier, while the Na+ in turn is pumped out by Na+–K+ ATPase, with a resultant net accumulation of KCl. At pathological K+ concentrations the KCl + NaCl carrier is less active because the Na+ driving force, its energy source, is reduced (owing to depolarization by K+). However, the Donnan equilibrium across the cell membrane is heavily disturbed, which leads to passive KCl accumulation. The results suggest that volume changes in cultured glial cells during exposure to high K+ should be taken into consideration since they disguise K+ accumulation when only ion activity is measured.

scholarly journals Kinetic characterization of the Escherichia coli oligopeptidase A (OpdA) and the role of the Tyr607 residue

2010 ◽  
Vol 500 (2) ◽  
pp. 131-136 ◽  
Author(s):  
Ricardo Z. Lorenzon ◽  
Carlos E.L. Cunha ◽  
Marcelo F. Marcondes ◽  
Maurício F.M. Machado ◽  
Maria A. Juliano ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Kinetic Characterization

Molecular and kinetic characterization of histamine transport into adult rat cultured astrocytes

2012 ◽  
Vol 61 (3) ◽  
pp. 415-422 ◽  
Author(s):  
Katja Perdan-Pirkmajer ◽  
Sergej Pirkmajer ◽  
Katarina Černe ◽  
Mojca Kržan
Keyword(s):  
Kinetic Characterization ◽  
Adult Rat ◽  
Cultured Astrocytes

scholarly journals Identification and Characterization of the Na+/H+ Antiporter NhaS3 from the Thylakoid Membrane of Synechocystis sp. PCC 6803

2009 ◽  
Vol 284 (24) ◽  
pp. 16513-16521 ◽  
Author(s):  
Kenta Tsunekawa ◽  
Toshiaki Shijuku ◽  
Mitsuo Hayashimoto ◽  
Yoichi Kojima ◽  
Kiyoshi Onai ◽  
...  
Keyword(s):  
Thylakoid Membrane ◽  
Ion Homeostasis ◽  
E Coli ◽  
Subjective Night ◽  
Genes Encoding ◽  
Ph Range ◽  
Identification And Characterization ◽  
Pcc 6803

Na+/H+ antiporters influence proton or sodium motive force across the membrane. Synechocystis sp. PCC 6803 has six genes encoding Na+/H+ antiporters, nhaS1–5 and sll0556. In this study, the function of NhaS3 was examined. NhaS3 was essential for growth of Synechocystis, and loss of nhaS3 was not complemented by expression of the Escherichia coli Na+/H+ antiporter NhaA. Membrane fractionation followed by immunoblotting as well as immunogold labeling revealed that NhaS3 was localized in the thylakoid membrane of Synechocystis. NhaS3 was shown to be functional over a pH range from pH 6.5 to 9.0 when expressed in E. coli. A reduction in the copy number of nhaS3 in the Synechocystis genome rendered the cells more sensitive to high Na+ concentrations. NhaS3 had no K+/H+ exchange activity itself but enhanced K+ uptake from the medium when expressed in an E. coli potassium uptake mutant. Expression of nhaS3 increased after shifting from low CO2 to high CO2 conditions. Expression of nhaS3 was also found to be controlled by the circadian rhythm. Gene expression peaked at the beginning of subjective night. This coincided with the time of the lowest rate of CO2 consumption caused by the ceasing of O2-evolving photosynthesis. This is the first report of a Na+/H+ antiporter localized in thylakoid membrane. Our results suggested a role of NhaS3 in the maintenance of ion homeostasis of H+, Na+, and K+ in supporting the conversion of photosynthetic products and in the supply of energy in the dark.

Kinetic Characterization of Wild-Type and S229A Mutant MurB:  Evidence for the Role of Ser 229 as a General Acid†

Biochemistry ◽  
1997 ◽  
Vol 36 (4) ◽  
pp. 796-805 ◽  
Author(s):  
Timothy E. Benson ◽  
Christopher T. Walsh ◽  
Vincent Massey
Keyword(s):  
Kinetic Characterization ◽  
Wild Type ◽  
General Acid

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

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