title: Acidocalcisomes are functionally linked to the contractile vacuole of Dictyostelium discoideum.
abstract: The mass-dense granules of Dictyostelium discoideum were shown to contain large amounts of phosphorus, magnesium, and calcium, as determined by x-ray microanalysis, either in situ or when purified using iodixanol gradient centrifugation. The high phosphorus content was due to the presence of pyrophosphate and polyphosphate, which were also present in the contractile vacuoles. Both organelles also possessed a vacuolar H(+)-ATPase, an H(+)-pyrophosphatase, and a Ca(2+)-ATPase, as determined by biochemical methods or by immunofluorescence microscopy. The H(+)-pyrophosphatase activity of isolated mass-dense granules was stimulated by potassium ions and inhibited by the pyrophosphate analogs aminomethylenediphosphonate and imidodiphosphate and by KF and N-ethylmaleimide in a dose-dependent manner. The mass-dense granules and the contractile vacuole appeared to contact each other when the cells were submitted to hyposmotic stress. Acetazolamide inhibited the carbonic anhydrase activity of the contractile vacuoles and prolonged their contraction cycle in a dose-dependent manner. Similar effects were observed with the anion exchanger inhibitor 4,4' -diisothiocyanatodihydrostilbene-2, 2' -disulfonic acid and the vacuolar H(+)-ATPase inhibitor bafilomycin A(1). Together, these results suggest that the mass-dense granules of D. discoideum are homologous to the acidocalcisomes described in protozoan parasites and are linked to the function of the contractile vacuole.
authors.affiliation: Laboratory of Molecular Parasitology, Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA.
authors.forename: Norma
authors.initials: N
authors.lastname: Marchesini
authors.forename: Felix A
authors.initials: FA
authors.lastname: Ruiz
authors.forename: Mauricio
authors.initials: M
authors.lastname: Vieira
authors.forename: Roberto
authors.initials: R
authors.lastname: Docampo
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D003285:Contractile Proteins / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004023:Dictyostelium / Q000737:chemistry* / Q000378:metabolism*; D004164:Diphosphonates / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D043564:Inorganic Pyrophosphatase; D007477:Ions / Q000378:metabolism; D018942:Macrolides; D008274:Magnesium / Q000378:metabolism; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D015388:Organelles / Q000737:chemistry* / Q000378:metabolism; D009995:Osmosis; D010758:Phosphorus / Q000378:metabolism; D011485:Protein Binding; D011755:Pyrophosphatases / Q000378:metabolism; D013312:Stress, Physiological; D014283:Triiodobenzoic Acids / Q000494:pharmacology; D014617:Vacuoles / Q000378:metabolism*; D014965:X-Rays
chemical_list: D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D003285:Contractile Proteins; D003432:Cross-Linking Reagents; D004164:Diphosphonates; D004791:Enzyme Inhibitors; D007477:Ions; D018942:Macrolides; D014283:Triiodobenzoic Acids; C057620:bafilomycin A; C016514:imidodiphosphonic acid; D010758:Phosphorus; C018564:dihydro-DIDS; C040929:bafilomycin A1; D011755:Pyrophosphatases; D043564:Inorganic Pyrophosphatase; C044834:iodixanol; D008274:Magnesium; D005033:Ethylmaleimide; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium