Changes in membrane permeability during semliki forest virus induced cell fusion

The infection of Aedes albopictus cells by Semliki Forest virus (SFV) is a non lytic event. Exposure of infected cells to mildly acidic pH (<6.2) leads to syncytium formation. This polykaryon formation is accompanied by an influex of protons into the cells (Kempfet al. Biosci. Rep. 7, 761–769, 1987). We have further investigated this permeability change using various fluorescent or radiolabeled compounds. A significant, pH dependent increase of the membrane permeability to low molecular weight compounds (Mr<1000) was observed when infected cells were exposed to a pH<6.2. The pH dependence of the peremability change was very similar to the pH dependence of cell-cell fusion. The permeability change was sensitive to divalent cations, protons and anionic antiviral drugs such as trypan blue. The nature of this virus induced, pH dependent permeability change is discussed.