title: Platelet Ca2+ homeostasis: Na+-Ca2+ exchange in plasma membrane vesicles.
abstract: A vesicular plasma membrane-enriched fraction obtained from human platelets exhibited 45Ca2+ uptake in exchange for intravesicular Na+. The rate of Ca2+ uptake was linear up to 4 sec. The apparent Km for Ca2+ was 22 microM and the Vmax 280 pmol/mg/sec. Ca2+ efflux from Ca2+ loaded vesicles was obtained upon dilution into a NaCl but not a KCl medium. The extent of Ca2+ uptake was monotonically increased as the pH increased from 6 to 9. Na+-Ca2+ exchange was shown to be electrogenic. Ca2+ uptake was distinguished from binding by the induction of Ca2+ release after A23187 addition. These findings support a role for Na+-Ca2+ exchange in human platelet Ca2+ transport.
mesh_terms: D001792:Blood Platelets / Q000502:physiology* / Q000648:ultrastructure; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002458:Cell Fractionation / Q000379:methods; D002462:Cell Membrane / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D007474:Ion Exchange / Q000187:drug effects; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D002132:Calcium Radioisotopes; D014634:Valinomycin; D000001:Calcimycin; D012964:Sodium; D002118:Calcium