SCANNING MICROSPECTROFLUOROMETRY OF RHODAMINE-123 IN MULTIDRUG-RESISTANT CELLS

Scanning microspectrofluorometry has been developed to perform the map ping of fluorescence spectra from all locations in a living cell. This new method has been applied to study the molecular environment of rho damine 123 (R123) in sensitive (K562, CEM) and multidrug-resistant (K5 62-R, CEM/VLB(100)) tumor cells.All cells exposed to R123 showed a sim ilar distribution of fluorescence in the perinuclear region. A lower c ytoplasmic fluorescence intensity corresponding to a reduced drug accu mulation was observed in resistant cells, as expected in the multidrug resistance process. Fluorescence emission spectra of R123 are useful to probe the polarity of the R123 environment. Thus, fluorescence spec tra of R123-treated cells have been analyzed as a linear combination o f model spectra: R123 in water and R123 in tensio-active Triton X-100. In sensitive cells, emission spectra of R123 underwent a red shift, e quivalent to those observed in isolated coupled mitochondria. This sug gests the formation of a complex in hydrophobic sites. In contrast, R1 23 spectra were less shifted in resistant cells, showing two types of both hydrophobic and hydrophilic binding sites. This could be related to an intracellular redistribution of R123 in resistant cells. (C) 199 4 Wiley-Liss, Inc.