title: Interactions between inositol tris- and tetrakis-phosphates. Effects on intracellular Ca2+ mobilization in SH-SY5Y cells.
abstract: The potential Ca2(+)-releasing activity of the inositol tetrakisphosphates Ins(1,3,4,6)P4 and DL-Ins(1,4,5,6)P4 and the inositol pentakisphosphate Ins(1,3,4,5,6)P5 and their effect on Ins(1,4,5)P3- and DL-Ins (1,3,4,5)P4-mediated Ca2+ release were examined in permeabilized SH-SY5Y human neuroblastoma cells. Neither DL-Ins(1,4,5,6)P4 nor Ins(1,3,4,5,6)P5 exhibit Ca2(+)-releasing activity at concentrations up to 10 microM, but Ins(1,3,4,6)P4 releases Ca2+ dose-dependently, with an EC50 value (conen, giving half-maximal effect) of 5.92 +/- 0.47 microM. Maximal response by this tetrakisphosphate (49 +/- 2.5%) is significantly less than that seen with Ins(1,4,5)P3 (60 +/- 3%) and is achieved at a concentration of 30 microM. In the presence of this concentration of Ins(1,3,4,6)P4 the EC50 value for Ins(1,4,5)P3-mediated Ca2+ release increases from 0.12 +/- 0.02 microM to 2.11 +/- 0.51 microM, providing evidence that this naturally occurring inositol tetrakisphosphate may recognize and exhibit its Ca2(+)-releasing activity via the Ins(1,4,5)P3 receptor. DL-Ins(1,3,4,5)P4, however, at its maximally effective concentration (10 microM) does not significantly affect Ins(1,4,5)P3-mediated Ca2+ release, and therefore appears to mediate its Ca2(+)-mobilizing action through a receptor distinct from that for Ins(1,4,5)P3.
authors.affiliation: Department of Pharmacology, University of Leicester, U.K.
authors.forename: D J
authors.initials: DJ
authors.lastname: Gawler
authors.forename: B V
authors.initials: BV
authors.lastname: Potter
authors.forename: R
authors.initials: R
authors.lastname: Gigg
authors.forename: S R
authors.initials: SR
authors.lastname: Nahorski
mesh_terms: D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D002460:Cell Line; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000494:pharmacology*; D007700:Kinetics; D009447:Neuroblastoma; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear
chemical_list: D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C081655:inositol-1,3,4,5-tetrakisphosphate; C081653:inositol-1,3,4,6-tetrakisphosphate; C081651:inositol-1,4,5,6-tetrakisphosphate; C013571:inositol pentaphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium