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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 3681

Jonathan I. Ravdin, Cheryl F. Murphy, and Paul H. Schlesinger; The Cellular Regulation of Vesicle Exocytosis by Entamoeba histolytica. J.Protozool. 35(1):159-163, 1988

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We studied the cellular regulation of vesicle exocytosis by Entamoeba histolytica utilizing release of endocytosed [125iodine] (125I) labeled tyrosine conjugated dextran; [125I-dextran] entered the acid pH vesicles of the amebae and was not degraded during these studies. Exocytosis was temperature dependent with 74%, 36%, 4%, and 0% of [125I-dextran] released after 120 min at 37 degrees C, 31 degrees C, 25 degrees C, and 4 degrees C, respectively (P<0.01 for each). Exocytosis at 37 degrees C was inhibited by cytochalasin D (10 µg/ml), EDTA (10 mM), or the putative intracellular calcium antagonist TMB-8 (250 µM) (P<0.01 for each at >/_ 60 min). Calcium ionophore A23187 (1 µM) enhanced exocytosis at 5 and 15 min (P<0.01). Elevation of vesicle pH with NH4Cl (10 mM) had no effect on release of [125I-dextran]; phorbol myristate acetate (10E-6 M) increased exocytosis by 46% at 30 min (P<0.01). Centrifugation of amebae with target Chinese hamster ovary cells resulted in decreased [125I-dextran] release into the cell supernatant after 30 and 60 min at 37 degrees C (by 40% and 42%, respectively, P<0.01); release of [125I-dextran] returned to control values with addition of 1.0 g% galactose or GalNac but not with mannose or N-acetyl-D-glucosamine. Amebic phagocytosis of serum-exposed latex beads had no effect on release of dextran by amebae (n=16). Exocytosis of acid pH vesicles by E. histolytica is temperature-, microfilament-, and calcium-dependent, and stimulated by phorbol esters.