The Cellular Regulation of Vesicle Exocytosis by Entamoeba histolytica^,

ABSTRACT. 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°C, 31°C, 25°C, and 4°C, respectively (P < 0.01 for each). Exocytosis at 37°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 (10⁻⁶ 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°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.