title: Calcium regulates inositol 1,3,4,5-tetrakisphosphate production in lysed thymocytes and in intact cells stimulated with concanavalin A.
abstract: Lysed mouse thymocytes release [3H]inositol 1,4,5 trisphosphate from [3H]inositol-labelled phosphatidyl inositol 4,5-bisphosphate in response to GTP gamma S, and rapidly phosphorylate [3H]inositol 1,4,5-trisphosphate to [3H]inositol 1,3,4,5-tetrakisphosphate. The rate of phosphorylation is increased approximately 7-fold when the free [Ca2+] in the lysate is increased from 0.1 to 1 microM, the range in which the cytosolic free [Ca2+] increases in intact thymocytes in response to the mitogen concanavalin A. Stimulation of the intact cells with concanavalin A also results in a rapid and sustained increase in the amount of inositol 1,3,4,5-tetrakisphosphate, and a much smaller transient increase in 1,4,5-trisphosphate. Lowering [Ca2+] in the medium from 0.4 mM to 0.1 microM before addition of concanavalin A reduces accumulation of inositol 1,3,4,5-tetrakisphosphate by at least 3-fold whereas the increase in inositol 1,4,5-trisphosphate is sustained rather than transient. The data imply that in normal medium the activity of the inositol 1,4,5-trisphosphate kinase increases substantially in response to the rise in cytosolic free [Ca2+] generated by concanavalin A, accounting for both the transient accumulation of inositol 1,4,5-trisphosphate and the sustained high levels of inositol 1,3,4,5-tetrakisphosphate. Inositol 1,3,4,5-tetrakisphosphate is a strong candidate for the second messenger for Ca2+ entry across the plasma membrane. This would imply that the inositol polyphosphates regulate both Ca2+ entry and intracellular Ca2+ release, with feedback control of the inositol polyphosphate levels by Ca2+.
authors.forename: Y
authors.initials: Y
authors.lastname: Zilberman
authors.forename: L R
authors.initials: LR
authors.lastname: Howe
authors.forename: J P
authors.initials: JP
authors.lastname: Moore
authors.forename: T R
authors.initials: TR
authors.lastname: Hesketh
authors.forename: J C
authors.initials: JC
authors.lastname: Metcalfe
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007295:Inositol Phosphates / Q000096:biosynthesis*; D007700:Kinetics; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D013403:Sugar Phosphates / Q000096:biosynthesis*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D013873:Thionucleotides; C081655:inositol-1,3,4,5-tetrakisphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D002118:Calcium