CALCIUM AND HYDROGEN-ION CONCENTRATIONS IN THE PARASITOPHOROUS VACUOLES OF EPITHELIAL-CELLS INFECTED WITH THE MICROSPORIDIAN ENCEPHALITOZOON HELLEM

Microsporidia of the genus Encephalitozoon undergo merogony and sporog ony in a parasitophorous vacuole within the host cell. Cultured green monkey kidney cells infected with Encephalitozoon hellem were loaded w ith the fluorescent dyes fura-2 or BCECF in order to measure intracell ular concentrations of calcium and hydrogen ions respectively. Both th e parasitophorous vacuole calcium concentration and pH values resemble d those of the host cell cytoplasm in infected cells. Calcein entered the parasitophorous vacuole but not other host cell vacuoles or parasi te stages within the parasitophorous vacuole. The lack of a pH or calc ium concentration gradient across the parasitophorous vacuole membrane and the permeability of this membrane to a large anion such as calcei n suggest that the vacuole membrane surrounding E. hellem resembles th at surrounding some other intracellular parasites such as Toxoplasma g ondii. A potential role is discussed for the parasitophorous vacuole c alcium concentration in germination in situ.