title: Inositol polyphosphates and intracellular calcium release.
abstract: The hydrolysis of inositol lipids triggered by the occupation of cell surface receptors generates several intracellular messengers. Many different inositol phosphate isomers accumulate in stimulated cells. Of these D-myo-inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) is responsible for discharging Ca2+ from intracellular stores. Specific membrane binding sites for Ins 1,4,5-P3 have been detected. The properties of these sites and their possible relationship to the calcium release process is reviewed. Ins 1,4,5-P3 binding sites may be present in discrete subcellular structures ("calciosomes"). Kinetic and some electrophysiological evidence indicates that Ins 1,4,5-P3 acts to open a Ca2+ channel. Recent progress on the purification of the receptor from neuronal tissues is summarized. Phosphorylation of Ins 1,4,5-P3 by a specific kinase results in the production of D-myo-inositol 1,3,4,5-tetraphosphate (Ins 1,3,4,5-P4). This inositol phosphate has been reported to increase the entry of Ca2+ across the plasma membrane, activate nonspecific ion channels in the plasma membrane, alter the Ca2+ content of the Ins 1,4,5-P3-releasable store, and bind to and alter the activity of certain enzymes. These data and the possible biological significance of Ins 1,3,4,5-P4 are discussed.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104.
authors.forename: S K
authors.initials: SK
authors.lastname: Joseph
authors.forename: J R
authors.initials: JR
authors.lastname: Williamson
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism*; D013403:Sugar Phosphates / Q000378:metabolism*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium