title: Reversal of the Ca2+ pump of blood platelets.
abstract: In this study, the endoplasmic Ca2+ transport ATPase of blood platelets was compared with the Ca2+ ATPase of sarcoplasmic reticulum skeletal muscle. Similar to the muscle enzyme, the Ca2+ ATPase from platelets was found to catalyse an ATP<-->P(i) exchange both in the presence and in the absence of a transmembrane Ca2+ gradient. When platelet vesicles are loaded with Ca2+ and diluted in medium containing ADP, P(i) and EGTA, the ATPase catalyses Ca2+ efflux coupled to synthesis of ATP. The stoichiometry between Ca2+ ion released and ATP synthesized by platelet Ca2+ ATPase is 1, while that of skeletal muscle is 2. Thapsigargin, a specific inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+ ATPases, inhibited both the Ca(2+)-dependent ATPase activity and the reversal of the platelet Ca2+ pump. The possibility is discussed that the differences observed between the two transport systems is related to the distinct amino acid sequences of the enzymes.
authors.affiliation: Departamento de Bioquimica, Universidade Federal do Rio de Janeiro, Cidade Universitaría, Ilha do Fundao, Brasil.
authors.forename: J C
authors.initials: JC
authors.lastname: Benech
authors.forename: H
authors.initials: H
authors.lastname: Wolosker
authors.forename: L
authors.initials: L
authors.lastname: de Meis
mesh_terms: D000255:Adenosine Triphosphate / Q000097:blood; D001792:Blood Platelets / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000097:blood; D015220:Calcium Channels / Q000097:blood*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000097:blood; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D018482:Muscle, Skeletal / Q000201:enzymology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
chemical_list: D015220:Calcium Channels; D013729:Terpenes; D000001:Calcimycin; D004533:Egtazic Acid; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium