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 acetoxy methyl esters (AM-esters) of ion-sensitive dyes provided us with a noninvas ive method for investigation of the permeability of the parasitophorous vac uole membrane (PVM) and simultaneous measurement of Ca2+ and H+ concentrati ons in different compartments of the infected cells. The distribution patte rns of the cleaved membrane-impermeant dyes argue against the existence of nonselective pores in the PVM. There is also no indication of a parasitopho rous duct connecting the vacuolar space with extracellular media. The pH in side 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 2 4 h the Ca2+ response to extracellular adenosine triphosphate (ATP) was sig nificantly reduced, indicating influences on the host cell's intracellular signaling.