Oncosis in MA104 cells is induced by rotavirus infection through an increase in intracellular Ca2+ concentration

Rotavirus infection modifies the metabolism and ionic homeostasis of the host cell. First, there is an induction of viral synthesis with a parallel shutoff of cell protein production, followed by an increase of plasma membrane Ca2+ permeability, thereby inducing an increase of free cytoplasmic and sequestered Ca2+ concentrations. Cell death follows at a later stage. We studied the role of the increase in Ca2+ concentration in cell death. An elevation of extracellular Ca2+ concentration during infection induced an increase in [Ca2+]i and potentiated cell death. Buffering the increases in [Ca2+]i with BAPTA added at 6 h p.i. reduced the cytopathic effect without inhibiting viral protein synthesis and infectious particle production. Metoxyverapamil (D600), a Ca2+ channel inhibitor, added at 1 h p.i. reduced Ca2+ permeability, the increases in [Ca2+]i, and cell death produced by infection without modifying viral protein synthesis and infectious titer. Thapsigargin, the inhibitor of Ca(2+)-ATPase of endoplasmic reticulum, potentiated the increase of [Ca2+]i and accelerated the time course of cell death. Double staining with fluorescein diacetate and ethidium bromide or acridine orange and ethidium bromide showed that infected MA104 cells had lost plasma membrane integrity without DNA fragmentation or formation of apoptotic bodies. These results support the hypothesis that the increase in [Ca2+]i due to a product of viral protein synthesis triggers the chain of events that leads to cell death by oncosis.