title: Two novel types of calcium release from skeletal sarcoplasmic reticulum by phosphatidylinositol 4,5-biphosphate.
abstract: In both the heavy and light fractions of fragmented sarcoplasmic reticulum (SR) vesicles from the fast skeletal muscle, about 27 min after beginning the active Ca2+ uptake, the extravesicular Ca2+ concentration suddenly increased to reach a steady level (delayed Ca2+ release). Phosphatidylinositol 4,5-bisphosphate (PIP2) not only shortened the time to delayed Ca2+ release but also induced prompt Ca2+ release from the heavy fraction of SR. Delayed Ca2+ release and prompt Ca2+ release stimulated by 100 microM PIP2 were not modified by ruthenium red. PIP2 (>0.1 microM) markedly accelerated the rate of 45Ca2+ efflux from SR vesicles in a concentration-dependent manner. The PIP(2)-induced 45Ca2+ efflux was potentiated by ruthenium red but profoundly inhibited by La3+. The concentration-response curve for Ca2+ or Mg2+ in PIP2-induced 45Ca2+ release was clearly different from that in the Ca(2+)-induced Ca2+ release. PIP2 caused a concentration-dependent increase in Ca2+ release from SR of chemically skinned fibers from skeletal muscle. Furthermore, [3H]ryanodine or [3H]methyl-7-bromoeudistomin D (MBED) binding to SR was increased by PIP2 in a concentration-dependent manner. These observations present the first evidence that PIP2 most likely activates two types of SR Ca2+ release channels whose properties are entirely different from those of Ca(2+)-induced Ca2+ release channels (the ryanodine receptor 1).
authors.affiliation: Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Aramaki, Sendai, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ohizumi
authors.forename: Y
authors.initials: Y
authors.lastname: Hirata
authors.forename: A
authors.initials: A
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000494:pharmacology*; D011817:Rabbits; D012433:Ryanodine / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D012433:Ryanodine; D002118:Calcium