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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Keywords: H+ flux ; K+ flux ; Ca2+-pump ; sarcoplasmic reticulum ; rabbit muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The release of H+ during the oxalate-supported Ca2+ uptake in sarcoplasmic reticulum vesicles is kinetically coincident with the initial phase of Ca2+ accumulation. The Ca2+ uptake is increased and the H+ release is decreased in the presence of KCl and other monovalent chloride salts as expected for a H+-monovalent cation exchange. The functioning of the Ca2+-pump is disturbed by the presence of potassium gluconate and, to a lesser extent, of choline chloride. These salts do not inhibit the ATPase activity of Ca2+-permeable vesicles, suggesting a charge imbalance inhibition which is specially relevant in the case of gluconate. Therefore, K+, and also Cl−, appear to be involved in secondary fluxes during the active accumulation of Ca2+. The microsomal preparation seems homogeneous with respect to the K+-channel, showing an apparent rate constant for K+ release of approximately 25 s−1 measured with the aid of86Rb+ tracer under equilibrium conditions. A Rb+ efflux, sensitive to Ca2+-ionophore, can be also detected during the active accumulation of Ca2+. The experimental data suggest that both monovalent cations and anions are involved in a charge compensation during the Ca2+ uptake and H+ release. Fluxes of these highly permeable ions would contribute to cancel the formation of a resting membrane potential through the sarcoplasmic reticulum membrane.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Keywords: Clomipramine ; tricyclic antidepressants ; Ca2+-pump ; sarcoplasmic reticulum ; skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The Ca2+-pumping activity of skeletal sarcoplasmic reticulum vesicles is half-maximallyinhibited by 120 μM clomipramine, 250 μM desipramine, and 500 μM imipramine or trimipramine.The inhibition is attributed to the dihydrodibenzazepine moiety, since3-(dimethylamino)propionitrile, reproducing the aliphatic amine chain, has no inhibitory action. The inhibitionis shown as a marked decrease of Ca2+ binding at equilibrium in theabsence of ATP and asa reduction of phosphorylation of the Ca2+-free conformation byinorganic phosphate. Therefore,the drug effect is consistent with preferential interaction of tricyclic antidepressants withthe Ca2+-free conformation of the nonphosphorylated enzyme. An additional decrease in theapparent rate constant of enzyme dephosphorylation, i.e., in the release of phosphate fromATP during enzyme cycling was also noticed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 25 (1986), S. 8083-8089 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 32 (1993), S. 8553-8559 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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