title: Secretion, subcellular localization and metabolic status of inorganic pyrophosphate in human platelets. A major constituent of the amine-storing granules.
abstract: The platelet content of PPi is 1.90 +/- mumol/10(11) platelets (S.E.M., n = 19) or about 10.5 nmol/mg of protein, several hundred times that found for rat liver. Some 80% of this PPi is secreted by platelets treated with thrombin with a time course and dose-response relationship similar to secretion of ATP, ADP and 5-hydroxytryptamine (serotonin) from the platelet dense granules. During platelet aggregation induced by ADP and adrenaline, substantial amounts of PPi were secreted, but no release of acid hydrolases was observed. Subcellular-fractionation studies showed that the PPi is highly enriched in the same fraction that contains the storage organelles which store ATP, ADP, Ca2+ and 5-hydroxytryptamine. Inorganic pyrophosphatase was present mainly in the soluble fraction and in the mitochondria. Secretion studies done with platelets prelabelled with [32P]Pi showed that the sequestered PPi was relatively metabolically inactive, as is the ATP and ADP in the storage organelles. The possible participation of PPi in the formation of a bivalent-cation-nucleotide complex associated with amine storage is discussed.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000588:Amines / Q000097:blood*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003094:Collagen / Q000494:pharmacology; D011756:Diphosphates / Q000097:blood*; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D011755:Pyrophosphatases / Q000097:blood; D013347:Subcellular Fractions / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology
chemical_list: D000588:Amines; D011756:Diphosphates; D000244:Adenosine Diphosphate; D003094:Collagen; D013917:Thrombin; D011755:Pyrophosphatases; D004837:Epinephrine