Mitochondrial response and calcium ion change in apoptotic insect cells induced by SfaMNPV

Mitochondrial responses and changes of calcium ions in apoptotic insect SL-1 cells induced by Syngrapha falcifera multiple nuclear polyhedrosis virus (SfaMNPV) are reported in this paper. By using Rhodamine 123 as a fluorescent labeling probe, flow cytometry analysis and confocal laser scanning microscope observation we observed that the mitochondrial transmembrane potential (DYm) began to decrease in SL-1 cells at 4 h post infection and DYm reduced continuously with the extension of virus infection. Western blotting indicated that the Bcl-2 level in the mitochondria gradually declined and was down- regulated. Cells undergoing apoptosis were found to have an elevation of cytochrome c in the cytosol and a corresponding decrease in the mitochondria, which indicated that cytochrome c was released from mitochondria into cytosol. These results suggest that mitochondrion-mediated apoptotic signal transduction pathway exists in apoptotic insect cell induced by SfaMNPV. Cytosolic free calcium (Ca2+]i) concentration rapidly increased after SfaMNPV infection and the elevated calcium was tested to come partly from extracelllular cal-cium ion influx. Flow cytometry analysis indicated that the apoptosis in SL-1 cells was not influenced by established cytosolic calcium clamped conditions and the EGTA inhibit-ing calcium influx. Therefore, neither the elevation of cytoso-lic calcium ion nor extracellular calcium entry was the in-ducing factor of apoptosis, which hinted that the depletion of ER Ca2+ store contributed to SL-1 cell apoptosis induced by SfaMNPV.