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  • 1
    Electronic Resource
    Electronic Resource
    Aldosterone and thyroid hormone modulation of α1-, β1-mRNA, and Na,K-Pump sites in rabbit distal colon epithelium. Evidence for a novel mechanism of escape from the effect of hyperaldosteronemia (1993)
    Springer
    The journal of membrane biology 133 (1993), S. 203-211 
    Details
    ISSN: 1432-1424
    Keywords: sodium pump ; Na,K-ATPase ; aldosterone ; thyroid hormone ; distal colon epithelium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Aldosterone and thyroid hormone regulation of Na,K-pump biosynthesis has been examined in the distal colon epithelium of rabbits. Qualitative analysis of α-subunit isoform distribution (α1, α2, α3) detected only the α1-mRNA in the distal colon epithelium and outer renal medulla, while all three isoforms were observed in rabbit brain. A low-sodium diet led to a rise in serum aldosterone from 0.6 nm to 1.4–1.9 nm and an increase of α1-mRNA to 162%, β1-mRNA to 120%, and the number of Na,K-pump units as determined by specific [3H]-ouabain binding to 182% of control by the second day of the diet. While aldosterone levels remained elevated, a spontaneous decrease in serum levels of T3 and T4 to 50–60% of control from the third day of the diet was followed by downregulation of β1-mRNA to 55–67%, α1-mRNA to 63–105%, and of [3H]-ouabain binding to 103% of control, suggesting that a reduced rate of synthesis of the β1-subunit is rate limiting for Na,K-pump biosynthesis. Substitution with T3 (10 μg/kg) at the seventh day with transient restoration of serum T3 to control levels, led to rapid accumulation of β1-mRNA to 152%, of α1-mRNA to 135%, and of the number of Na,K-pump units to 153% of control. This is consistent with thyroid hormone having a permissive role for the aldosterone stimulation of Na,K-pump biosynthesis. Reduced rates of β-subunit transcription due to low thyroid hormone levels appear to provide a mechanism for escape from the effect of hyperaldosteronemia on the number of Na,K-pump units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232020
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  • 2
    Electronic Resource
    Electronic Resource
    Localization of E1–E2 conformational transitions of sarcoplasmic reticulum Ca-ATPase by tryptic cleavage and hydrophobic labeling (1986)
    Springer
    The journal of membrane biology 93 (1986), S. 85-92 
    Details
    ISSN: 1432-1424
    Keywords: conformational change ; trypsin ; size exclusion HPLC ; amino-acid sequence ; trifluoromethyl-[125I]iodophenyldiazirine ; CrATP ; vanadate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Tryptic peptides of Ca-ATPase in Et and E2 conformational states (Andersen, J. P., Jørgensen, P. L.,J. Membrane Biol. 88:187–198 (1985)) have been isolated by size exclusion high performance liquid chromatography in sodium dodecyl sulfate. This permitted unambiguous localization of a conformational sensitive tryptic split at Arg 198 by N-terminal amino acid sequence analysis. Other splits at Arg 505 and at Arg 819-Lys 825 were insensitive to E1–E2 transitions. Tryptic cleavage of Ca-ATPase after phosphorylation by inorganic phosphate showed that this enzyme form has a conformation similar to that of the vanadate-bound E2 state, both in membranous and in soluble monomeric Ca-ATPase. Hydrophobic labeling of Ca-ATPase in sarcoplasmic reticulum vesicles with the photoactivable reagent trifluoromethyl-[125I]iodophenyl-diazirine indicated that E2 and E2V states are more exposed to the membrane phase than E1 and E1P (Ca2+-occluded) states. The preferetial hydrophobic labeling in E2 forms was found to be localized in the A1 tryptic fragment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871021
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  • 3
    Electronic Resource
    Electronic Resource
    Ca2+ activation and pH dependence of a maxi K+ channel from rabbit distal colon epithelium (1993)
    Springer
    The journal of membrane biology 136 (1993), S. 9-21 
    Details
    ISSN: 1432-1424
    Keywords: Maxi K+ channel ; Calcium ; pH ; Charybdotoxin ; Rabbit distal colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract To determine if their properties are consistent with a role in regulation of transepithelial transport, Ca2+-activated K+ channels from the basolateral plasma membrane of the surface cells in the distal colon have been characterized by single channel analysis after fusion of vesicles with planar lipid bilayers. A Ca2+-activated K+ channel with a single channel conductance of 275 pS was predominant. The sensitivity to Ca2+ was strongly dependent on the membrane potential and on the pH. At a neutral pH, the K 0.5 for Ca2+ was raised from 20nm at a potential of 0 mV to 300nm at −40 mV. A decrease in pH at the cytoplasmic face of the K+ channel reduced the Ca2+ sensitivity dramatically. A loss of the high sensitivity to Ca2+ was also observed after incubation with MgCl2, possibly a result of dephosphorylation of the channels by endogenous phosphatases. Modification of the channel protein may thus explain the variation in Ca2+ sensitivity between studies on K+ channels from the same tissue. High affinity inhibition (K 0.5=10nm) by charybdotoxin of the Ca2+-activated K+ channel from the extracellular face could be lifted by an outward flux of K+ through the channel. However, at the ion gradients and potentials found in the intact epithelium, charybdotoxin should be a useful tool for examination of the role of maxi K+ channels. The high sensitivity for Ca2+ and the properties of the activator site are in agreement with an important regulatory role for the high conductance K+ channel in the epithelial cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00241485
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  • 4
    Electronic Resource
    Electronic Resource
    Reconstitution in phospholipid vesicles of calcium-activated potassium channel from outer renal medulla (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 105-112 
    Details
    ISSN: 1432-1424
    Keywords: Ca-activated K+ channel ; solubilization ; reconstitution ; thick ascending limb of Henle's loop ; calmodulin inhibitors ; trypsin ; pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A barium-sensitive Ca-activated K+ channel in the luminal membrane of the tubule cells in thick ascending limb of Henle's loop is required for maintenance of the lumen positive transepithelial potential and may be important for regulation of NaCl reabsorption. In this paper we examine if the K+ channel can be solubilized and reconstituted into phospholipid vesicles with preservation of its native properties. The K+ channel in luminal plasma membrane vesicles can be quantitatively solubilized in CHAPS at a detergent/protein ratio of 3. For reconstitution, detergent is removed by passage over a column of Sephadex G 50 (coarse). K+-channel activity is assayed by measurement of86Rb+ uptake against a large opposing K+ gradient. The reconstituted K+ channel is activated by Ca2+ in the physiological range of concentration (K1/2∼2×10−7 m at pH 7.2) as found for the K+ channel in native plasma membrane vesicles and shows the same sensitivity to inhibitors (Ba2+, trifluoperazine, calmidazolium, quinidine) and to protons. Reconstitution of the K+ channel into phospholipid vesicles with full preservation of its native properties is an essential step towards isolation and purification of the K+-channel protein. Titration with Ca2+ shows that most of the active K+ channels in reconstituted vesicles have their cytoplasmic aspect facing outward in contrast to the orientation in plasma membrane vesicles, which requires also addition of Ca2+ ionophore in order to observe Ca2+ stimulation. The reconstituted K+ channel is highly sensitive to tryptic digestion. Brief digestion leads to activation of the K+ channel in absence of Ca2+, to the level of activity seen with saturating concentrations of Ca2+. This tryptic split is located in a cytoplasmic aspect of the K+ channel that appears to be involved in opening and closing the K+ channel in response to Ca2+ binding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869155
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational states of sarcoplasmic reticulum Ca2+-ATPase as studied by proteolytic cleavage (1985)
    Springer
    The journal of membrane biology 88 (1985), S. 187-198 
    Details
    ISSN: 1432-1424
    Keywords: protein structure ; trypsin ; chymotrypsin ; Ca2+ transport ; phosphorylation ; energy transduction ; detergent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Conformational states in sarcoplasmic reticulum Ca2+-ATPase have been examined by tryptic and chymotryptic cleavage. High affinity Ca2+ binding (E1 state) exposes a peptide bond in the A fragment of the polypeptide chain to trypsin. Absence of Ca2+ (E2 state) exposes bonds in the B fragment, which are protected by binding of Mg2+ or ATP. After phosphorylation from ATP the tryptic cleavage pattern depends on the predominant phosphoenzyme species present. ADP-sensitive E1P and ADP-insensitive E2P have cleavage patterns identical to those of unphosphorylated E1 and E2, respectively, indicating that two major conformational states are involved in Ca2+ translocation. The transition from E1P to E2P is inhibited by secondary tryptic splits in the A fragment, suggesting that parts of this fragment are of particular importance for the energy transduction process. The tryptic cleavage patterns of phosphorylated forms of detergent solubilized monomeric Ca2+-ATPase were similar to those of the membrane-bound enzyme, indicating that Ca2+ translocation depends mainly on structural changes within a single peptide chain. On the other hand, the protection of the second cleavage site as observed after vanadate binding to membranous Ca2+-ATPase could not be achieved in the soluble monomeric enzyme. Shielding of this peptide bond may therefore be due to protein-protein interactions in the semicrystalline state of the vanadate-bound Ca2+-ATPase in membranous form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868432
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  • 6
    Electronic Resource
    Electronic Resource
    STRUCTURE AND MECHANISM OF Na,K-ATPASE: Functional Sites and Their Interactions (2003)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 65 (2003), S. 817-849 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract The cell membrane Na,K-ATPase is a member of the P-type family of active cation transport proteins. Recently the molecular structure of the related sarcoplasmic reticulum Ca-ATPase in an E1 conformation has been determined at 2.6 A resolution. Furthermore, theoretical models of the Ca-ATPase in E2 conformations are available. As a result of these developments, these structural data have allowed construction of homology models that address the central questions of mechanism of active cation transport by all P-type cation pumps. This review relates recent evidence on functional sites of Na,K-ATPase for the substrate (ATP), the essential cofactor (Mg2+ ions), and the transported cations (Na+ and K+) to the molecular structure. The essential elements of the Ca-ATPase structure, including 10 transmembrane helices and well-defined N, P, and A cytoplasmic domains, are common to all PII-type pumps such as Na,K-ATPase and H,K-ATPases. However, for Na,K-ATPase and H,K-ATPase, which consist of both alpha- and beta-subunits, there may be some detailed differences in regions of subunit interactions. Mutagenesis, proteolytic cleavage, and transition metal-catalyzed oxidative cleavages are providing much evidence about residues involved in binding of Na+, K+, ATP, and Mg2+ ions and changes accompanying E1-E2 or E1-P-E2-P conformational transitions. We discuss this evidence in relation to N, P, and A cytoplasmic domain interactions, and long-range interactions between the active site and the Na+ and K+ sites in the transmembrane segments, for the different steps of the catalytic cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.65.092101.142558
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  • 7
    Electronic Resource
    Electronic Resource
    STRUCTURE OF THE Na, K PUMP: CRYSTALLIZATION OF PURE MEMBRANE-BOUND Na, K-ATPase AND IDENTIFICATION OF FUNCTIONAL DOMAINS OF THE α-SUBUNIT (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 402 (1982), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1982.tb25743.x
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  • 8
    Electronic Resource
    Electronic Resource
    Dissociation between compensatory renal growth and induction of (Na++K+-ATPase in rat kidney after uninefrectomy (1971)
    Springer
    Cellular and molecular life sciences 27 (1971), S. 527-528 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Nach Uninephrektomie und bilateraler Adrenalektomie entsteht eine Dissoziation zwischen der Nierenvergrösserung und der (Na++K+)-ATPase Aktivität. Es besteht wahrscheinlich kein Zusammenhang zwischen der Nierenvergrösserung und der Induktion von (Na++K+)-ATPase. Auch in der vergrösserten Niere sind die Nebennierenhormone notwendig, um die (Na++K+)-ATPase zu erhalten.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02147578
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  • 9
    Electronic Resource
    Electronic Resource
    Rabbit distal colon epithelium: III. Ca2+-activated K+ channels in basolateral plasma membrane vesicles of surface and crypt cells (1990)
    Springer
    The journal of membrane biology 117 (1990), S. 275-283 
    Details
    ISSN: 1432-1424
    Keywords: Ca2+-activated K+ channels ; rabbit distal colon membranes ; reconstitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In the mammalian distal colon, the surface epithelium is responsible for electrolyte absorption, while the crypts are the site of secretion. This study examines the properties of electrical potential-driven86Rb+ fluxes through K+ channels in basolateral membrane vesicles of surface and crypt cells of the rabbit distal colon epithelium. We show that Ba2+-sensitive, Ca2+-activated K+ channels are present in both surface and crypt cell derived vesicles with half-maximal activation at 5×10−7 m free Ca2+. This suggests an important role of cytoplasmic Ca2+ in the regulation of the bidirectional ion fluxes in the colon epithelium. The properties of K+ channels in the surface cell membrane fraction differ from those of the channels in the crypt cell derived membranes. The peptide toxin apamin inhibits Ca2+-activated K+ channels exclusively in surface cell vesicles, while charybdotoxin inhibits predominantely in the crypt cell membrane fraction. Titrations with H+ and tetraethylammonium show that both high-and low-sensitive86Rb+ flux components are present in surface cell vesicles, while the high-sensitive component is absent in the crypt cell membrane fraction. The Ba2+-sensitive, Ca2+-activated K+ channels can be solubilized in CHAPS and reconstituted into phospholipid vesicles. This is an essential step for further characterization of channel properties and for identification of the channel proteins in purification procedures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868457
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