Effect of fixatives on fracture plane in red blood cells

SUMMARY The effect of various fixatives on the path of the fracture plane during freeze‐fracturing was studied in red blood cells. In unfixed cells the fracture plane ran between the leaflets of the plasma membrane (membrane‐fractured cells) in 66% of the cells and across the cells (cross‐fractured cells) in 34%. Formaldehyde fixation greatly increased the proportion of cross‐fractured cells (up to 80%) and osmium tetroxide acted in a similar manner (up to 90% cross‐fractured cells). With glutaraldehyde fixation, small, smooth patches of cross‐linked material were often seen on the convex (A) fracture faces. Holes were found on the corresponding concave (B) fracture faces. Uranyl acetate had no effect on the fracture plane or distribution of particles. Thus osmium and formaldehyde might be a useful means of altering the fracture plane of membranes (e.g. in bacteria or enveloped viruses).