Sodium-Calcium Exchange in Platelet Plasma Membrane Vesicles
Unstimulated platelets maintain submicromolar concentration of cytosolic Ca2+ (~100 μM) and a steep plasma membrane Ca2+ gradient. Since passive inward diffusion of Ca2+ will cause platelet activation, mechanisms in addition to Ca2+ sequestration by endoplasmic reticulum must exist to remove Ca2+ from cytosol. In other tissues low cytosolic Ca2+ is achieved, in part, by plasma membrane ATP-dependent Ca2+ efflux1,2 and Na+-Ca2+ exchange3,4. Although platelets possess Ca2+-Mg2+-ATPase activity, the available evidence suggests that this enzyme is present only in the inner membranes5,6. Whether Na+-Ca2+ exchange activity occurs in platelets is not known. We investigated the involvement of Na+-Ca2+ exchange in this process. This study establishes that platelet membranes enriched in plasma membrane markers exhibited Na+-Ca2+ exchange activity.
KeywordsCalcium Uptake Uptake Medium Platelet Membrane Adenosine Triphosphatase Submicromolar Concentration
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