Are osmotic forces involved in influenza virus-cell fusion?

The kinetics of the fusion process of unsealed and resealed erythrocyte ghosts with influenza virus (A/PR8/34, A/Chile 1/83) were measured under hypotonic, isotonic and hypertonic conditions using a recently developed fluorescence assay (Hoekstra et al. (1984) Biochemistry 23:5675-5681]. No correlation between the external osmotic pressure and kinetics and extent of fusion was observed. Influenza viruses fuse as effectively with unsealed ghosts as with resealed ghosts. It is concluded that osmotic forces as well as osmotic swelling of cells are not necessary for virus-cell membrane fusion.