title: Involvement of extracellular calcium in phosphatidylserine exposure during apoptosis.
abstract: The appearance of phosphatidylserine (PS) on the outer surface of apoptotic cells is an important signal for their ingestion. In platelets, elevation of intracellular Ca2+ with thapsigargin can trigger large amounts of PS exposure within minutes. We detected PS exposure in U937 promonocytes and Jurkat T-cells after incubation with thapsigargin, but in only 10% of the cells, and it took up to 6 h to occur. Tumor necrosis factor and anti-Fas antibody rapidly trigger apoptosis in these cells, and chelation of extracellular Ca2+ with 5 mM EGTA inhibited PS exposure by 65% and 50%, respectively. Chelation of intracellular Ca2+ with BAPTA-AM had no effect. Other parameters of apoptosis, including cell blebbing, shrinkage, nuclear fragmentation, activation of the ICE-like proteases, and fodrin cleavage, were not inhibited by extracellular EGTA. We conclude that while an elevation of intracellular Ca2+ is an ineffective trigger of apoptosis in the cells investigated, extracellular Ca2+ is required for efficient PS exposure during apoptosis.
authors.affiliation: Institute of Environmental Medicine, Division of Toxicology, Karolinska Institutet, Stockholm, Sweden. mark.hampton@imm.ki.se
authors.forename: M B
authors.initials: MB
authors.lastname: Hampton
authors.forename: D M
authors.initials: DM
authors.lastname: Vanags
authors.forename: M I
authors.initials: MI
authors.lastname: Pörn-Ares
authors.forename: S
authors.initials: S
authors.lastname: Orrenius
mesh_terms: D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D010718:Phosphatidylserines / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism
chemical_list: D010718:Phosphatidylserines; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D004533:Egtazic Acid; D019284:Thapsigargin; D002118:Calcium