Evidence that phospholipid protects ram spermatozoa from cold shock at a plasma membrane site

Adding phospholipid dispersions to washed ram spermatozoa provided immediate protection against cold shock as judged by the effect on motility. Re-washing the spermatozoa free of dispersed lipid rendered then susceptible to cold shock. Analysis of the spermatozoa showed that exogenous phospholipid had not become interpolated into the cell membranes. The ratio of phospholipid to cholesterol in the spermatozoon was not changed when dispersed phospholipid was added and stayed the same during incubation for 3 h at 37 degrees C. It is concluded that the protective effect of phospholipid against cold shock in ram spermatozoa is due to a 'loose' interaction of the lipid structures with the plasma membrane of the cells.