The University of Iowa Carver College of Medicine
Hypotonic propidium iodide solutions are not recommended for use in apoptotic experiments where DNA content measurement is the goal (not to be confused with isotonic propidium iodide used for live/dead discrimination). Hypotonic solutions yield nuclei by lysing the cell membrane and thereby releasing the contents of the cytoplasm. In cells undergoing apoptosis, DNA fragments and apoptotic bodies can be present in the prepared sample making it difficult to separate them from nuclei on the basis of fluorescence and light scatter. Therefore, a whole cell preparation is recommended for apoptotic assays where DNA fragmentation results in a hypodiploid peak in the DNA fluorescence histogram.