Requirement for Vacuolar H-ATPase Activity and Ca 2 Gradient during Entry of Rotavirus into MA104 Cells

endosomal Ca 2 concentration on virus entry was studied by inhibiting the endosomal H-ATPase with bafilomycin A1 and/or increasing the extracellular calcium reservoir by addition of 10 mM CaEGTA. Rotavi- rus--sarcin coentry was inhibited by bafilomycin A1 and by addition of 10 mM CaEGTA. These effects were additive. These substances induced a significant inhibition of infectivity without affecting virus binding and postentry steps. These results are compatible with the interpretation that bafilomycin A1 and CaEGTA block rotavirus penetration from the endosome into the cytoplasm and support our hypothesis of a Ca 2 -dependent endocytosis model.