title: Obligatory Role of Early Ca(2+) Responses in H2O2-Induced β-Cell Apoptosis.
abstract: Our previous study using apoptosis analysis suggested that Ca(2+) release through inositol 1,4,5-trisphosphate (IP3) receptors and the subsequent Ca(2+) influx through store-operated channels (SOCs) constitute a triggering signal for H2O2-induced β-cell apoptosis. In the present study, we further examined the obligatory role of early Ca(2+) responses in β-cell apoptosis induction. H2O2 induced elevation of the cytosolic Ca(2+) concentration ([Ca(2+)]c) consisting of two phases: an initial transient [Ca(2+)]c elevation within 30 min and a slowly developing one thereafter. The first phase was almost abolished by 2-aminoethoxydiphenylborate (2-APB), which blocks IP3 receptors and cation channels including SOCs, while the second phase was only partially inhibited by 2-APB. The inhibition by 2-APB of the second phase was not observed when 2-APB was added 30 min after the treatment with H2O2. 2-APB also largely inhibited elevation of the mitochondrial Ca(2+) concentration ([Ca(2+)]m) induced by H2O2 when 2-APB was applied simultaneously with H2O2, but not when applied 30 min after H2O2 application. In addition, 2-APB inhibited the release of mitochondrial cytochrome c to the cytosol induced by H2O2 when 2-APB was applied simultaneously with H2O2 but not 30 min post-treatment. H2O2-induced [Ca(2+)]m elevation and cell death were not inhibited by Ru360, an inhibitor of the mitochondrial calcium uniporter (MCU). These results suggest that the H2O2-induced initial [Ca(2+)]c elevation, occurring within 30 min and mediated by Ca(2+) release through IP3 receptors and subsequent Ca(2+) influx through SOCs, leads to [Ca(2+)]m elevation, possibly through a mechanism independent of MCU, thereby inducing cytochrome c release and consequent apoptosis.
authors.affiliation: Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka.
authors.forename: Taiji
authors.initials: T
authors.lastname: Sato
authors.forename: Yukiko K
authors.initials: YK
authors.lastname: Kaneko
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Sawatani
authors.forename: Akiko
authors.initials: A
authors.lastname: Noguchi
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Ishikawa
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism; D006861:Hydrogen Peroxide; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D051381:Rats
chemical_list: D001896:Boron Compounds; D053496:Inositol 1,4,5-Trisphosphate Receptors; D045304:Cytochromes c; D006861:Hydrogen Peroxide; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium