Greetings, We use BCECF AM and carboxy SNARF-1 AM for intracellular pH measurements with a FACS Calibur. The FL1/FL3 ratio is used for BCECF and the FL3/FL2 ratio for SNARF. The calibration method is the high K+/nigericin technique. Recently we made a comparison and found that the resting pHi of K562 cells was 6.72 if measured with BCECF and 7.01 (average values) if measured with SNARF under the same experimental conditions. This is almost an 0.3 units difference that we can hardly explain. Autofluorescence signals are small at all wavelengths compared to the SNARF or BCECF fluorescence intensities. Has anyone had similar experiences with these or other pH dyes/cell lines? Explanation, suggestions, comments will be greatly appreciated. Thank you in advance, Laszlo Grama PhD student gramal@apacs.pote.hu University Medical School of Pecs Institute of Biophysics Szigeti ut 12. H-7643 Pecs, HUNGARY Tel/Fax: (36) 72 314017
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