title: Myo-inositol 1,3,4,5-tetrakisphosphate can independently mobilise intracellular calcium, via the inositol 1,4,5-trisphosphate receptor: studies with myo-inositol 1,4,5-trisphosphate-3-phosphorothioate and myo-inositol hexakisphosphate.
abstract: Myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] acts as a full agonist for Ca2+ release in saponin-permeabilised SH-SY5Y neuroblastoma cells. Studies were conducted in the presence of myo-inositol hexakisphosphate (InsP6, 10 microM), to inhibit the Ins(1,3,4,5)P(4)-3-phosphatase catalysed back conversion of Ins(1,3,4,5)P4 to Ins(1,4,5)P3. HPLC analysis confirmed that Ins(1,3,4,5)P4 releases the entire content of Ins(1,4,5)P3-sensitive intracellular Ca2+ stores, independent of 3-phosphatase activity. Further we utilised racemic myo-inositol 1,4,5-trisphosphate-3-phosphorothioate [DL-Ins(1,3,4,5)P(4)-3S], a novel intrinsically Ins(1,3,4,5)P(4)-3-phosphatase resistant Ins(1,3,4,5)P4 analogue. DL-Ins(1,3,4,5)P(4)-3S specifically displaced [3H]Ins(1,4,5)P3 from bovine adrenal cortex Ins(1,4,5)P3 binding sites (IC50 = 889 nM, compared to Ins(1,4,5)P3, IC50 = 4.4 nM and Ins(1,3,4,5)P4, IC50 = 152 nM). DL-Ins(1,3,4,5)P(4)-3S was a full agonist for Ca2+ release (EC50 = 4.7 microM), being 90- and 2-fold less potent than Ins(1,4,5)P3 and Ins(1,3,4,5)P4 (with InsP6), respectively. DL-Ins(1,3,4,5)P(4)-3S will be an important tool for identification of potentially exclusive Ins(1,3,4,5)P4 second messenger functions, since its resistance to 3-phosphatase action precludes the inconvenient artefact of steady state Ins(1,4,5)P3 generation.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Wilcox
authors.forename: E M
authors.initials: EM
authors.lastname: Whitham
authors.forename: C
authors.initials: C
authors.lastname: Liu
authors.forename: B V
authors.initials: BV
authors.lastname: Potter
authors.forename: S R
authors.initials: SR
authors.lastname: Nahorski
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000494:pharmacology*; D009946:Organothiophosphorus Compounds / Q000494:pharmacology*; D010833:Phytic Acid / Q000494:pharmacology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D009946:Organothiophosphorus Compounds; D018160:Receptors, Cytoplasmic and Nuclear; C081655:inositol-1,3,4,5-tetrakisphosphate; C054737:inositol 1,4,5-triphosphorothioate; D010833:Phytic Acid; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium