How was cell membrane protein mobility facilitated?

By Frye and Edidin, using sendal virus to facilitate formation of heterokaryon in cell culture, which is a cell resulting from fusion of two cells from different species, labeling cell surface antigens with fluorochromes that help distinguish them in EM, Where it was noticed that first human and mouse antigens were at opposite poles, but then both became uniformly distrubuted, so proteins are not fixed at precise positions but able to move.