Osmotic homeostasis in Dictyostelium discoideum: excretion of amino acids and ingested solutes.
The response to osmotic stress in axenically cultured Dictyostelium discoideum was examined. Hypoosmotic buffers elicited two changes in the large (approximately 50 mM) cytosolic pool of amino acids: a) the total size of the pool diminished, while b) about half of the initial pool was excreted. Hyperosmotic stress had the opposite effect. Among the predominant amino acids in the pool were glycine, alanine and proline. Putrescine, the major diamine, was neither excreted nor modulated. Recently ingested radioactive amino acids were excreted in preference to those in the cytoplasm, suggesting that the endocytic pathway might be involved in water excretion. Furthermore, hypoosmotic stress stimulated the selective excretion of small, membrane-impermeable fluorescent dyes which had been ingested into endocytic vacuoles. Caffeine inhibited the excretion of the fluorophores but not the amino acids. We conclude that the response of Dictyostelium to osmotic stress is complex and includes both modulation of the cytoplasmic amino acid pool and the excretion of amino acids and other small solutes from the endocytic pathway.
Steck
T L
TL
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637, USA. t-steck@uchicago.edu
Chiaraviglio
L
L
Meredith
S
S
D000409:Alanine / Q000378:metabolism; D000588:Amines / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology*; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011700:Putrescine / Q000032:analysis; D012965:Sodium Chloride / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases; D014617:Vacuoles / Q000378:metabolism*
D000588:Amines; D000596:Amino Acids; D005456:Fluorescent Dyes; D002110:Caffeine; D018698:Glutamic Acid; D012965:Sodium Chloride; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D000409:Alanine; D011700:Putrescine