STREPTAVIDIN-TRICOLOR IS A RELIABLE MARKER FOR NONVIABLE CELLS SUBJECTED TO PERMEABILIZATION OR FIXATION

Cell death is normally accompanied by loss of integrity of the cell me mbrane. Concomitant loss of osmotic pressure and permeability for DNA binding dyes like propidium iodide make it possible to distinguish via ble from nonviable cells. However, after permeabilization for intracel lular staining or after fixation of the cells, we find that propidium iodide leaks out of nonviable cells and is transferred to formerly via ble cells. Cell size cannot be used for examining viability in permeab ilized or heterogeneous cell populations. Here we show that streptavid intricolor enters specifically and irreversibly into dead cells, and i s not transferred to formerly viable cells after fixation or permeabil ization. Therefore, streptavidin-tricolor can be a useful dead-cell ma rker in experimental situations where conventional methods fail to dis tinguish between viable and nonviable cells. (C) 1994 Wiley-Liss, Inc.