Propidium iodide is a red-fluorescent dye that can be used to stain cells.
Propidium iodide is a cell-membrane impermeable dye with characteristic excitation maximum at 535 nm and emission maximum at 617 nm which intercalates with nucleic acids with a stoichiometry of one dye per 4-5 base pairs with little sequence preference. Propidium iodide has evidenced of having no toxic effects on neurons, being today’s most common marker for membrane integrity and cell viability when applied prior to fixation (pre-fixation propidium iodide staining method). The pre-fixation staining has been widely used for quantitative assessments of neuronal cell decline in models of acute neurodegeneration, visualized as intensely labeled PI+-pycnotic nuclei of degenerating neurons . Propidium iodide cannot cross the membrane of live cells, making it useful to measure the percentage of apoptotic cells by flow-cytometric analysis. The flow cytometric data shows an excellent correlation with the results obtained with both electrophoretic and colorimetric methods. This new rapid, simple and reproducible method proves useful for assessing apoptosis of specific cell populations in heterogeneous tissues such as bone marrow, thymus and lymph nodes