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Figure 6.7 Top panel: phase contrast images of HeLa cells exposed to 100 mM of [Eu
2
(L7)
3
]
(top row) or to 3.2 mM acridine orange (bottom row) for 0-24 h at 37
C. Bottom panel: time-
resolved luminescence microscopy images of live HeLa cells incubated with 100 mMof
[Eu
2
(L7)
3
] for 0.25-24 h at 37
C.
Reproduced from ref. [77] with permission,
#
2008 Royal
Society of Chemistry.
eventually gather around the nucleus, on one side of the cells. The vesicles have sizes
ranging from 0.5 to 2.0mm. The helicates remain in the vesicles, that is they do not diffuse
into the cytoplasm or into the nucleus. Co-localization experiments with several organic
dyes led to the conclusion that the majority of [Eu
2
(L7)
3
] stained vesicles are localized
within the endoplasmic reticulum and not in the Golgi apparatus [77].
The mechanism of uptake has been identified as an endocytotic process by superposing
images with the helicate and with a fluorescent organic marker for secondary endosomes
and lysosomes. Further evidence was gathered by incubating the cells at low temperature,
at which endocytosis does not take place, and by adding endocytosis inhibitors. The concen-
tration of [Eu
2
(L7)
3
] in cells was estimated from time-resolved luminescence assays similar
to luminescence immunoassays and was found to be on the order of 8
10
16
mol cell
1
.
The leakage of helicates out of the cells was determined with time-lapse experiments and
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