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  • Title: Two different Ca2+ transport systems are associated with plasma and intracellular human platelet membranes.
    Author: Enouf J, Bredoux R, Bourdeau N, Levy-Toledano S.
    Journal: J Biol Chem; 1987 Jul 05; 262(19):9293-7. PubMed ID: 2954959.
    Abstract:
    Platelet plasma and intracellular membrane fractions were isolated from a mixed membrane fraction after sucrose cushion centrifugation. Their previous identification through biochemical and immunological characterization is now confirmed by sodium dodecyl sulfate electrophoresis of the membrane proteins which reveals a different protein profile. The two associated calcium transport systems showed a different time course and exhibited different oxalate sensitivity. The plasma membranes are not permeable to potassium oxalate but the Ca2+ uptake was stimulated by potassium oxalate in intracellular membranes. We then focused on the study of the plasma membrane-associated Ca2+-activated ATPase which shows the following characteristics: a linearity in the time course until 30 min, an apparent affinity toward calcium of about 10(-7) M without detectable inhibition at higher concentrations, a maximal activity at pH 8, a high ATP requirement because the maximal response was obtained with 200 microM, and a high specificity toward ATP as energy donor. Taken together, these studies indicate the possible involvement of both a plasma membrane and a dense tubular system Ca2+-ATPase in the regulation of Ca2+ concentration in human platelets.
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