title: Challenge with high concentrations of cyclic AMP induces transient changes in the cytosolic free calcium concentration in Dictyostelium discoideum.
abstract: Dictyostelium discoideum cells use cyclic AMP (cAMP) for chemotactic signaling as well as for differentiation. The precise regulation of the cytosolic Ca2+ concentration ([Ca2+]i) seems to play a key role for both processes. We performed single cell measurements of [Ca2+]i in amoebae that were starved in suspension for various times and scrape-loaded with the Ca2+ indicator fura-2. Stimulation of cells with cAMP at the concentration required to induce gene expression (> or = 100 microM) elicited a global transient increase in [Ca2+]i that depended on the presence of external Ca2+. Both vegetative and aggregation-competent cells displayed a rise in [Ca2+]i, with aggregation-competent cells responding more often than vegetative cells. Basal [Ca2+]i in the presence of Ca2+ was high in vegetative cells and declined during development; the cAMP-induced rise in [Ca2+]i was higher and lasted longer in vegetative cells than in aggregative cells. The addition of 2'-deoxy-cAMP, which binds to the cAMP receptor, induced an increase in [Ca2+]i, whereas the membrane-permeant analogue 8-bromo-cAMP that has a low affinity for the receptor but activates cAMP-dependent protein kinase had no effect. This indicates that the change in [Ca2+]i is mediated by the cell surface cAMP receptor. Since HC85 mutant cells, which lack the G alpha 2 subunit of the G-protein that couples the receptor to phospholipase C, also responded to stimulation with cAMP, the Ca2+ influx does not seem to be triggered by the phosphoinositide signaling cascade.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Fakultät für Biologie, Universität Konstanz, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Schlatterer
authors.forename: F
authors.initials: F
authors.lastname: Gollnick
authors.forename: E
authors.initials: E
authors.lastname: Schmidt
authors.forename: R
authors.initials: R
authors.lastname: Meyer
authors.forename: G
authors.initials: G
authors.lastname: Knoll
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism*; D004023:Dictyostelium / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D018715:Microscopy, Video; D015398:Signal Transduction / Q000502:physiology
chemical_list: C018892:2'-deoxy cyclic AMP; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D002118:Calcium