In answer to Michelle Miller, FSC signals decrease when the cell membrane becomes permeable to the external medium (thus altering the refractive index of the cytoplasm). Trypan Blue enters the cell when the membrane becomes permeable to Trypan Blue. Trypan Blue is larger than the small molecules (eg water, NaCl, etc) of the medium, and for this reason a cell may appear dead by FSC vs SSC before it appears dead by Trypan Blue. Since viability indicators are all of different sizes, death becomes relative..... Alice L. Givan Englert Cell Analysis Laboratory Dartmouth Medical School Lebanon, New Hampshire NH 03756 USA tel 603-650-7661 fax 603-650-6130 e-mail givan@dartmouth.edu
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