Cell membrane changes induced by the cytolytic peptide, melittin, are detectable by 90 degrees laser scatter.

The 90 degrees light scatter parameter of the flow cytometer was used to observe changes in the membrane of human lymphoblastoid cells (HMy2) as a result of the action of the cytolytic peptide, melittin. There was a rapid and concentration-dependent increase in 90 degrees light scatter after incubation of the cells with melittin, with the level of 90 degrees light scatter reaching a maximum after 2 min. Even after all the cells were killed, as determined by ethidium bromide incorporation, the 90 degrees light scatter continued to increase. Further, the 90 degrees light scatter changes were temperature dependent. The data are consistent with the formation of lipid vesicles, either attached to the cell membrane or intracellular, as confirmed by electron microscopy of cells treated with melittin. The results demonstrate the use of the flow cytometer to detect changes in the integrity of the cell membrane.