Relationship of free intracellular calcium to the cytolytic activity of Entamoeba histolytica

Abstract

Entamoeba histolytica adherence and destruction of host cells is required for in vivo pathogenicity; amebic in vitro adherence is mediated by a galactose- or N-acetyl-D-galactosamine-inhibitable surface lectin (Gal/GalNAc adherence lectin). Free intracellular Ca2+ concentration ([Ca2+](i)) was measured in living amebae and target cells during amebic cytolysis of Chinese hamster ovary (CHO) cells and human polymorphonuclear neutrophils by utilizing the Ca2+ probe Fura-2 and computer-enhanced digitized microscopy. Motile E. histolytica trophozoites had oscillatory increases in [Ca2+](i) in head or tail regions; however, there was no increase in regional or total amebic [Ca2+](i) upon contact with a target CHO cell. Target CHO cells and polymorphonuclear neutrophils demonstrated marked irreversible increases in [Ca2+](i) within 30 to 300 s following contact by an ameba (P < 0.01); increased [Ca2+](i) preceded the occurrence of nonspecific surface membrane permeability and death of the target cell. Target CHO cells contiguous on a monolayer to a cell contacted by an ameba experienced a rapid but reversible rise in [Ca2+](i) (P < 0.01) and were not killed. Galactose (40 mg/ml) totally abrogated the rise in target CHO cell [Ca2+](i) that followed contact by amebae (P < 0.01); immunoaffinity-purified amebic Gal/GalNAc adherence lectin (0.25 μg/ml) induced a rapid and reversible rise in CHO cell [Ca2+](i) (P < 0.01) which was inhibited by galactose. Amebic [Ca2+](i) was not elevated following parasite adherence to target cells; a rapid and substantial rise in target cell [Ca2+](i) occurred which was mediated, at least in part, by the Gal/GalNAc adherence lectin of the parasite and led to the death of target cells.