Osmotic Swelling Allows Fusion of Sendai Virions with Membranes of Desialized Erythrocytes and Chromaffin Granules

Sendai virus particles are able to fuse with Pronase-neuraminidase-treated human erythrocyte membranes as well as with vesicles obtained from chromaffin granules of bovine medulla. Fusion is inferred either from electron microscopic studies or from the observation that incubation of fluorescently labeled (bearing octadecyl Rhodamine B chloride) virions, with right-side-out erythrocyte vesicles (ROV) or with chromaffin granule membrane vesicles (CGMV), resulted in fluorescence dequenching. Fusion of Sendai virions with virus receptor depleted ROV was observed only under hypotonic conditions. Fusion with virus receptor depleted ROV required the presence of the two viral envelope glycoproteins, namely, the HN and F polypeptides. A 3-fold increase in the degree of fluorescence dequenching (virus-membrane fusion) was also obtained upon incubation of Sendai virions with CGMV in medium of low osmotic strength, This increase was not observed with inactivated, unfusogenic Sendai virions. The results of the present work demonstrate that, under hypotonic conditions, fusion between Sendai virions and biological membranes does not require the presence of specific receptors. Such fusion is characterized by the same features as fusion with and infection by Sendai virions of living cultured cells.