title: Cyclic AMP stimulates accumulation of inositol trisphosphate in Dictyostelium.
abstract: Previous studies indicated that in Dictyostelium amoebae signal transmission from cell surface cyclic AMP receptors to intracellular events concerned with chemotaxis involves inositol 1,4,5-trisphosphate (1,4,5-IP3): micromolar amounts of 1,4,5-IP3 or Ca2+ were found to mimic the effects of chemoattractants and 1,4,5-IP3 triggered release of Ca2+ from non-mitochondrial stores. Here we report a more direct test of the involvement of inositol phosphates. Intact amoebae were labelled with high specific activity [3H]inositol, then stimulated with the chemoattractant cyclic AMP at 22 degrees C and rapidly assayed for phosphorylated inositol products formed. Labelled IP3 was found to accumulate transiently after a pulse of 50 nM-cyclic AMP, with a peak at 15 s after stimulation and some (inconclusive) evidence for a more rapidly formed peak at 5 s or less. Inositol bisphosphate (IP2) showed a transient shallow peak at about 20 s. When the events of signal transmission were slowed down by incubation at 4 degrees C, the rapidly formed IP3 peak could be consistently seen at 5 s after stimulation and the second peak at 25-30 s. Further resolution of the IP3 peaks indicated the presence of IP4, which represented a major fraction of the peak accumulated at 5 s (4 degrees C). The results provide an important link in the chain of evidence connecting the cell surface cyclic AMP receptors, via IP3, with the Ca2+-activated events of chemotaxis.
authors.affiliation: Department of Biochemistry, University of Oxford, UK.
authors.forename: G N
authors.initials: GN
authors.lastname: Europe-Finner
authors.forename: P C
authors.initials: PC
authors.lastname: Newell
mesh_terms: D002633:Chemotaxis; D002852:Chromatography, Ion Exchange; D000242:Cyclic AMP / Q000494:pharmacology*; D004023:Dictyostelium / Q000187:drug effects* / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D013268:Stimulation, Chemical; D013403:Sugar Phosphates / Q000378:metabolism*
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D008094:Lithium; D000242:Cyclic AMP