Intracellular calcium and pH conditions of cultured cells infected with Eimeria bovis or E-separata

Loading of Eimeria bovis-infected Vero cells with membrane-permeant acetoxymethyl esters (AM-esters) of ion-sensitive dyes provided us with a noninvasive method for investigation of the permeability of the parasitophorous vacuole membrane (PVM) and simultaneous measurement of Ca2+ and H+ concentrations in different compartments of the infected cells. The distribution patterns of the cleaved membrane-impermeant dyes argue against the existence of nonselective pores in the PVM. There is also no indication of a parasitophorous duct connecting the vacuolar space with extracellular media. The pH inside the parasitophorous vacuole (PV) was lower than that in the cytoplasm of the host cell or the parasite, whereas the [Ca2+] in these compartments did not differ significantly. In HT29 cells infected with E. separata for 24 h the Ca2+ response to extracellular adenosine triphosphate (ATP) was significantly reduced, indicating influences on the host cell's intracellular signaling.