Membrane fusion induced by the membrane mobility agent, A₂C Differentiation between fusible and non-fusible cells Transfer of fusibility

Red cells of different species respond differently to the treatment with the membrane mobility agent, A₂C, with respect to both the A₂C interaction and the subsequent cell-cell interaction. Depending on whether both, one or neither of the processes are effective, some red cells (e.g., nucleated Leghorn hen red cells, rat red cells) fuse easily, some (human red cells) show morphological changes but do not fuse, and others (nucleated Rock hen red cells) show little or no response. Mixed fusion (i.e., between fusible cells of different species) is readily obtained, indicating that no species-specific recognition sites are required for A₂C-induced fusion. The potential for fusion is a transferable characteristic. In the presence of fusible cells, A₂C induces both heterologous and homologous fusion of otherwise 'non-fusible' cells. Electron micrographs of fusing cells after treatment with A₂C reveal 'onion-ring' structures ('whorls'), free of intramembranous protein particles but different from the smooth appearance of A₂C particles. Whorls are considered to arise from fusion-potent membrane areas. Fusion is apparent at multiple sites along the contact line between apposed membranes. The postulated appearance of vesicle-like structures along the fusion line (Kosower, E.M., Kosower, N.S. and Wegman, P. (1977) Biochim. Biophys. Acta 471, 311-329) is confirmed by micrographs. The mechanism of this fusion process is discussed and compared to other types of fusion process.