Chemistry Reference
In-Depth Information
7 Membrane Potential-Sensitive Aggregates of the Dyes
JC-1 and JC-9 for Mitochondria Imaging
Presently, the only commercially available dyes that are applied because of their
ability to form fluorescent aggregates are trimethine cyanines JC-1 and JC-9
(Fig.
11
)[
25
], the first one being studied much more extensively than the second
one. The dye JC-1 is known to form red-fluorescent (emission maximum at 590 nm)
J-aggregates in mitochondria possessing strong intramitochondrial negative poten-
tial, while upon depolarization of the mitochondrial membrane, the dye monomer
green emission (maximum at 527 nm) is observed [
25
]. JC-9 demonstrates similar
properties [
25
]. Such properties permit the application of these dyes for, e.g.,
detection of apoptotic electrical depolarization of mitochondria [
25
].
Mitochondria are the intracellular organelles in which ATP in synthesized.
These organelles are about 0.3-5
m long, surrounded by the double membrane.
For the intact mitochondria, their inner medium known as the matrix bears a high
value of negative potential
m
(about 150 mV [
25
]) as compared to the extra-
mitochondrial cell cytoplasm, while upon apoptosis the
DC
value is decreased. As
the dye JC-1 is positively charged and is able to penetrate the membrane, the
negative intramitochondrial potential induces the JC-1 uptake into the mitochondria
[
48
]. The larger the
DC
DC
value, the stronger is the uptake and the higher is the
concentration of JC-1 inside mitochondria, and upon increasing the dye concentra-
tion the J-aggregates are formed.
The concentration of J-aggregates is reported to increase linearly upon the
DC
increase in the range 30-180 mV [
49
]. It is not clear whether the aggregate for-
mation inside mitochondria occurs in aqueous phase or on the surface of some
intramitochondrial substructures. In each case, the ability of JC-1 to form fluores-
cent aggregates in aqueous solution was shown [
50
]. The structure of these aggre-
gates was studied and the assumption about the dye molecule packing in an
aggregate was made [
50
]. At lower
values, when the dye concentration inside
mitochondria is not enough to form the aggregates, the green fluorescence of dye
monomers is observed. On the basis of this dependence of the fluorescence color
on the mitochondrial membrane potential, regions of different electric potential
were observed on a single long mitochondrion with fluorescent microscopy [
48
].
DC
a
b
Cl
Cl
O
O
N
N
Cl
N
+
Cl
N
N
+
N
I
-
I
-
Fig. 11 Structures of dyes (a)5,5
0
,6,6
0
-tetrachloro-1,1
0
,3,3
0
-tetraethylbenzimidazolylcarbocyanine
iodide (JC-1), and (b) 3,3
0
-dimethyl-
a
-naphthoxacarbocyanine iodide (JC-9) sensitive to the
membrane potential
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