By releasing ADP, Acanthamoeba castellanii causes an increase in the cytosolic free calcium concentration and apoptosis in wish cells

The role played by soluble molecules that may participate in acanthamoebal cytopathogenicity has yet to be fully characterized. We demonstrate here th at Acanthamoeba castellanii trophozoites constitutively release ADP in the medium. Cell-free supernatants prepared from A. castellanii, by interaction with specific P-2y2 purinoceptors expressed on the Wish cell membrane, cau sed a biphasic rise in [Ca2+](i), extensive cell membrane blebbing, cytoske letal disorganization, and the breakdown of nuclei. Cell damage induced by amoebic supernatants was blocked by the P-2y2 inhibitor Suramin. The same r esults were found in Wish cells exposed to purified ADP. These findings sug gest that pathogenic free-living A. castellanii may have a cytopathic effec t on human epithelial cells through ADP release, by a process that begins w ith a rise of cytosolic free-calcium concentration, and culminates in apopt osis.