Hoechst 33342 dye uptake as a probe of membrane permeability in mammalian cells

The compound Hoechst 33342 (HO342), first developed as a pharmaceutical agent, was later shown to bind quantitatively to DNA and to become fluorescent on doing so. Unlike other fluorescent DNA stains, HO342 is readily taken up by living cells and is relatively non-toxic. Thus it can be used for DNA analysis of living cells which can then be sorted on the basis of DNA content and subsequently analyzed functionally. In the course of such studies the authors ran into an ''artefact'' in that they found subpopulations of cells stained with HO342 which differed in fluorescence intensity per cell but did not differ in DNA content