线粒体荧光探针信息大全 （Probes for Mitochondria）

包括各种常用探针，如JC-1，JC-9，TMRM，TMRE等

Mitochondria are found in eukaryotic cells, where they make up as much as 10% of the cell volume. They are pleomorphic organelles with structural variations depending on cell type, cell-cycle stage and intracellular metabolic state. The key function of mitochondria is energy production through oxidative phosphorylation (OxPhos) and lipid oxidation.1,2 Several other metabolic functions are performed by mitochondria, including urea production and heme, non-heme iron and steroid biogenesis, as well as intracellular Ca2+ homeostasis. Mitochondria also play a pivotal role in apoptosis ― a process by which unneeded cells are removed during development, and defective cells are selectively destroyed without surrounding organelle damage in somatic tissues 3�5 (Section 15.5). For many of these mitochondrial functions, there is only a partial understanding of the components involved, with even less information on mechanism and regulation.

Visualizing Mitochondria in Cells and Tissues

The morphology of mitochondria is highly variable. In dividing cells, the organelle can switch between a fragmented morphology with many ovoid-shaped mitochondria, as often shown in textbooks, and a reticulum in which the organelle is a single, many-branched structure. The cell cycle� and metabolic state�dependent changes in mitochondrial morphology are controlled by a set of proteins that cause fission and fusion of the organelle mass. Mutations in these proteins are the cause of several human diseases, indicating the importance of overall morphology for cell functioning (see Note 12.2 "Technical Focus: Mitochondria in Diseases"). Organelle morphology is also controlled by cytoskeletal elements, including actin filaments and microtubules. In nondividing tissue, overall mitochondrial morphology is very cell dependent, with mitochondria spiraling around the axoneme in spermatozoa, and ovoid bands of mitochondria intercalating between actomyosin filaments. There is emerging evidence of functionally significant heterogeneity of mitochondrial forms within individual cells.

The abundance of mitochondria varies with cellular energy level and is a function of cell type, cell-cycle stage and proliferative state. For example, brown adipose tissue cells,6 hepatocytes 7 and certain renal epithelial cells 8 tend to be rich in active mitochondria, whereas quiescent immune-system progenitor or precursor cells show little staining with mitochondrion-selective dyes.9 The number of mitochondria is reduced in Alzheimer's disease and their protein and nucleic acids are affected by reactive oxygen species, including nitric oxide 10 (Chapter 18).

Molecular Probes has a range of mitochondrion-selective dyes with which to monitor mitochondrial morphology and organelle functioning. The uptake of most mitochondrion-selective dyes is dependent on the mitochondrial membrane potential; nonyl acridine orange and possibly our MitoTracker Green FM, MitoFluor Green and MitoFluor Red 589 probes are notable exceptions, although their membrane potential�independent uptake and fluorescence has been questioned in some cell types.11,12 Mitochondrion-selective reagents enable researchers to probe mitochondrial activity, localization and abundance,13,14 as well as to monitor the effects of some pharmacological agents, such as anesthetics that alter mitochondrial function.15 Molecular Probes offers a variety of cell-permeant stains for mitochondria, as well as subunit-specific monoclonal antibodies directed against proteins in the oxidative phosphorylation (OxPhos) system, all of which are discussed below.

MitoTracker Probes: Fixable Mitochondrion-Selective Probes

Although conventional fluorescent stains for mitochondria, such as rhodamine 123 and tetramethylrosamine, are readily sequestered by functioning mitochondria, they are subsequently washed out of the cells once the mitochondrion's membrane potential is lost. This characteristic limits their use in experiments in which cells must be treated with aldehyde-based fixatives or other agents that affect the energetic state of the mitochondria. To overcome this limitation, Molecular Probes has developed MitoTracker probes ― a series of patented mitochondrion-selective stains that are concentrated by active mitochondria and well retained during cell fixation.16 Because the MitoTracker Orange, MitoTracker Red and MitoTracker Deep Red probes are also retained following permeabilization, the sample retains the fluorescent staining pattern characteristic of live cells during subsequent processing steps for immunocytochemistry, in situ hybridization or electron microscopy. In addition, MitoTracker reagents eliminate some of the difficulties of working with pathogenic cells because, once the mitochondria are stained, the cells can be treated with fixatives before the sample is analyzed.

Properties of MitoTracker Probes

MitoTracker probes are cell-permeant mitochondrion-selective dyes that contain a mildly thiol-reactive chloromethyl moiety. The chloromethyl group appears to be responsible for keeping the dye associated with the mitochondria after fixation. To label mitochondria, cells are simply incubated in submicromolar concentrations of the MitoTracker probe, which passively diffuses across the plasma membrane and accumulates in active mitochondria. Once their mitochondria are labeled, the cells can be treated with aldehyde-based fixatives to allow further processing of the sample; with the exception of MitoTracker Green FM, subsequent permeabilization with cold acetone does not appear to disturb the staining pattern of the MitoTracker dyes.

Molecular Probes offers seven MitoTracker reagents that differ in spectral characteristics, oxidation state and fixability (Table 12.2). MitoTracker probes are provided in specially packaged sets of 20 vials, each containing 50 µg for reconstitution as required.

Orange-, Red- and Infrared-Fluorescent MitoTracker Dyes

We offer MitoTracker derivatives of the orange-fluorescent tetramethylrosamine (MitoTracker Orange CMTMRos, M7510; Figure 12.3) and the red-fluorescent X-rosamine (MitoTracker Red CMXRos, M7512; Figure 12.4), as well as our newest derivatives, the MitoTracker Red 580 and MitoTracker Deep Red 633 probes (M22425, M22426; Figure 12.5, Figure 12.6). Because the MitoTracker Red CMXRos, MitoTracker Red 580 and MitoTracker Deep Red 633 probes produce longer-wavelength fluorescence that is well resolved from the fluorescence of green-fluorescent dyes, they are suitable for multicolor labeling experiments (Figure 1.45, Figure 8.7, Figure 12.7, Figure 12.8, Figure 12.9), including those that employ image deconvolution techniques (see Note 12.3 "Technical Focus: Wide-Field Deconvolution Microscopy"). Also available are chemically reduced forms of the tetramethylrosamine (MitoTracker Orange CM-H2 TMRos, M7511; Figure 12.10) and X-rosamine (MitoTracker Red CM-H2 XRos, M7513; Figure 12.11) MitoTracker probes. Unlike MitoTracker Orange CMTMRos and MitoTracker Red CMXRos, the reduced versions of these probes do not fluoresce until they enter an actively respiring cell, where they are oxidized to the fluorescent mitochondrion-selective probe and then sequestered in the mitochondria (Figure 12.12, Figure 12.50, Figure 15.13). The MitoTracker probes have proven useful for:

• Assaying the role of a kinesin-like protein on germ plasm aggregation in Xenopus oocytes 17

• Detecting early apoptosis (Section 15.5), which is marked by a disruption of mitochondrial transmembrane potential in all cell types studied 18�20

• Determining the mechanism by which mitochondrial shape is established and maintained in yeast 21

• Examining the time course of cell swelling in a human collecting-duct cell line using total internal reflection (TIR) microfluorimetry 22

• Localizing a novel kinesin motor protein involved in transport of mitochondria along microtubules 23

• Simultaneously observing fluorescent signals from a green-fluorescent protein (GFP) chimera and from the MitoTracker dye 24�27 (see Note 12.1 "Product Highlight: Fluorescent Probes for Use with GFP" in Section 12.1)

• Studying the localization of mitochondria in fibroblasts transformed with cDNA of wild-type and mutant kinesin heavy chains 28

• Visualizing mitochondria while characterizing the subcellular distribution of calcium channel subtypes in Aplysia californica bag cell neurons 29 and of the verotoxin B subunit in Vero cells 30

Our Vybrant Apoptosis Assay Kit #11 (V35116, Section 15.5) utilizes MitoTracker CMXRos in combination with Alexa Fluor 488 annexin V in a two-color assay of apoptotic cells (Figure 15.95). MitoTracker Orange CMTMRos and its reduced form CM-H2 TMRos have also been used to investigate the metabolic state of Pneumocystis carinii mitochondria.31 Following fixation, the oxidized forms of the tetramethylrosamine and X-rosamine MitoTracker dyes can be detected directly by fluorescence or indirectly with either anti-tetramethylrhodamine or anti�Texas Red dye antibodies (A6397, A6399; Section 7.4).

MitoTracker Green FM Probe

Mitochondria in cells stained with nanomolar concentrations of our patented MitoTracker Green FM dye (M7514) exhibit bright green, fluorescein-like fluorescence (Figure 12.13, Figure 12.33, Figure 14.68, Figure 16.21). The MitoTracker Green FM probe has the added advantage that it is essentially nonfluorescent in aqueous solutions and only becomes fluorescent once it accumulates in the lipid environment of mitochondria. Hence, background fluorescence is negligible, enabling researchers to clearly visualize mitochondria in live cells immediately following addition of the stain, without a wash step.

Unlike MitoTracker Orange CMTMRos and MitoTracker Red CMXRos, the MitoTracker Green FM probe appears to preferentially accumulate in mitochondria regardless of mitochondrial membrane potential in certain cell types, making it a possible tool for determining mitochondrial mass 32,33 (see Note 12.4 "Product Highlight: Estimating Mitochondrial Mass"). Furthermore, the MitoTracker Green FM dye is substantially more photostable than the widely used rhodamine 123 fluorescent dye and produces a brighter, more mitochondrion-selective signal at lower concentrations. Because its emission maximum is blue-shifted approximately 10 nm relative to the emission maximum of rhodamine 123, the MitoTracker Green FM dye produces a fluorescent staining pattern that should be better resolved from that of red-fluorescent probes in double-labeling experiments. The MitoTracker Green FM probe has been used to:

• Assay the differentiation state of Trypanosoma brucei bloodstream forms 34

• Demonstrate mitochondrion-selective labeling by avidin, streptavidin and anti-biotin antibodies 35

• Identify mitochondria in immunolocalization experiments in CHO cells 36

• Label sperm in order to determine the fate of sperm mitochondria during fertilization and subsequent embryo development 37�39 (Figure 12.13, Figure 12.14)

• Monitor mitochondrial distribution and transport in Tau-expressing CHO cells 40

• Study the regulation of calcium signaling by mitochondria in T lymphocytes 41

The mitochondrial proteins that are selectively labeled by the MitoTracker Green FM reagent have been separated by capillary electrophoresis.42

MitoFluor Probes: Nonfixable Mitochondrion-Selective Probes

MitoFluor Green Probe

As a companion to the MitoTracker Green FM derivative, we have developed the MitoFluor Green probe 11 (M7502), which has a structure similar to MitoTracker Green FM (Figure 12.15) but lacks its reactive chloromethyl moieties (Figure 12.16) and is not as well retained following fixation. As with MitoTracker Green FM, the MitoFluor Green probe can selectively stain mitochondria in live cells.11,43 The MitoFluor Green probe is also substantially more photostable than rhodamine 123, produces a brighter, more mitochondrion-selective signal at lower concentrations, and exhibits a blue-shifted emission maximum relative to that of rhodamine 123 that is better resolved from that of red-fluorescent probes in double-labeling experiments. Neither MitoTracker Green FM, nor the MitoFluor Green probe, appears to be retained after cell permeabilization.

Long-Wavelength MitoFluor Red Probes

We offer two mitochondria markers with long-wavelength fluorescence emission: MitoFluor Red 589 (M22424, Figure 12.17) and MitoFluor Red 594 44 (M22422, Figure 12.17). The MitoFluor Red 589 probe appears to accumulate in mitochondria regardless of the mitochondria's membrane potential, making it a potentially useful stain for estimating mitochondrial mass. This probe has absorption and emission peaks at 588 nm and 622 nm, respectively, and can be viewed with filter sets appropriate for the Texas Red dye. The MitoFluor Red 594 probe is a mitochondrial membrane potential�sensing dye that has been designed for optimal excitation by the 594 nm spectral line of the He�Ne laser. Both of these MitoFluor Red dyes provide a clear spectral window below 600 nm for dual labeling with green-fluorescent probes, including other site-selective probes or GFP chimeras.

MitoSOX Red Mitochondrial Superoxide Indicator

Mitochondrial superoxide is generated as a by-product of oxidative phosphorylation. In an otherwise tightly coupled electron transport chain, approximately 1�3% of mitochondrial oxygen consumed is incompletely reduced; those "leaky" electrons can quickly interact with molecular oxygen to form superoxide anion, the predominant ROS in mitochondria. Increases in cellular superoxide production have been implicated in cardiovascular diseases, including hypertension, atherosclerosis and diabetes-associated vascular injuries, as well as in neurodegenerative diseases such as Parkinson's, Alzheimer's and amyotrophic lateral sclerosis (ALS). The assumption that mitochondria serve as the major intracellular source of ROS has been based largely on experiments with isolated mitochondria rather than direct measurements in living cells.

MitoSOX Red mitochondrial superoxide indicator (M36008) is a novel fluorogenic dye for highly selective detection of superoxide in the mitochondria of live cells (Figure 12.18). MitoSOX Red reagent is live-cell permeant and is rapidly and selectively targeted to the mitochondria. Once in the mitochondria, MitoSOX Red reagent is oxidized by superoxide and exhibits bright red fluorescence upon binding to nucleic acids (excitation/emission maxima = 510/580 nm). MitoSOX Red reagent is readily oxidized by superoxide but not by other ROS- or reactive nitrogen species (RNS)�generating systems, and oxidation of the probe is prevented by superoxide dismutase. This reagent may enable researchers to distinguish artifacts of isolated mitochondrial preparations from direct measurements of superoxide generated in the mitochondria of live cells. It may also provide a valuable tool in the discovery of agents that modulate oxidative stress in various pathologies.

RedoxSensor Red CC-1 Stain

RedoxSensor Red CC-1 (2,3,4,5,6-pentafluorotetramethyldihydrorosamine, R14060; Figure 12.19) stain is a unique probe whose fluorescence localization appears to be based on a cell's cytosolic redox potential. Once it passively enters live cells, the RedoxSensor Red CC-1 stain may be oxidized in the cytosol to a red-fluorescent product (excitation/emission maxima ~540/600 nm), which then accumulates in the mitochondria. Alternatively, this nonfluorescent probe may be transported to the lysosomes where it is oxidized. The differential distribution of the oxidized product between mitochondria and lysosomes appears to depend on the redox potential of the cytosol.45 In proliferating cells, mitochondrial staining predominates; whereas in contact-inhibited cells, the staining is primarily lysosomal (Figure 18.15). The best method we have found to quantitate the distribution of the oxidized product is to use the mitochondrion-selective MitoTracker Green FM stain (M7514) in conjunction with the RedoxSensor Red CC-1 stain.45

JC-1 and JC-9: Dual-Emission Potential-Sensitive Probes

The green-fluorescent JC-1 probe (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide, T3168; Figure 22.13) exists as a monomer at low concentrations or at low membrane potential. However, at higher concentrations (aqueous solutions above 0.1 µM) or higher potentials, JC-1 forms red-fluorescent "J-aggregates" that exhibit a broad excitation spectrum and an emission maximum at ~590 nm (Figure 12.20, Figure 12.21, Figure 22.14). Thus, the emission of this cyanine dye can be used as a sensitive measure of mitochondrial membrane potential. Various types of ratio measurements are possible by combining signals from the green-fluorescent JC-1 monomer (absorption/emission maxima ~514/529 nm in water) and the J-aggregate (emission maximum 590 nm), which can be effectively excited anywhere between 485 nm and its absorption maximum at 585 nm (Figure 22.15). The ratio of red-to-green JC-1 fluorescence is dependent only on the membrane potential and not on other factors that may influence single-component fluorescence signals, such as mitochondrial size, shape and density. Optical filters designed for fluorescein and tetramethylrhodamine (Table 23.12) can be used to separately visualize the monomer and J-aggregate forms, respectively. Alternatively, both forms can be observed simultaneously using a standard fluorescein longpass optical filter set. Chen and colleagues have used JC-1 to investigate mitochondrial potentials in live cells by ratiometric techniques 46�48 (Figure 22.16). JC-1 has also been used to:

• Analyze the effects of drugs by flow cytometry 49

• Detect human encephalomyopathy 50

• Follow mitochondrial changes during apoptosis 51,52

• Investigate mitochondrial poisoning, uncoupling and anoxia 53

• Monitor effects of ellipticine on mitochondrial potential 54

JC-1 has been combined with the reagents in our LIVE/DEAD Sperm Viability Kit (L7011, Section 15.3) to permit simultaneous assessment of cellular integrity and mitochondrial function by flow cytometry.55 We also offer JC-1 as part of the MitoProbe JC-1 Assay Kit for flow cytometry (M34152, Section 22.3). We have discovered another mitochondrial marker, JC-9 (3,3'-dimethyl- -naphthoxazolium iodide, D22421; Figure 22.18), with a very different chemical structure (Figure 22.17) but similar potential-dependent spectroscopic properties. However, the green fluorescence of JC-9 is essentially invariant with membrane potential, whereas the red fluorescence is significantly increased at hyperpolarized membrane potentials.

Mitochondrion-Selective Rhodamines and Rosamines

Rhodamine 123

Rhodamine 123 (R302; FluoroPure Grade, R22420; Figure 12.22) is a cell-permeant, cationic, fluorescent dye that is readily sequestered by active mitochondria without inducing cytotoxic effects.56 Uptake and equilibration of rhodamine 123 is rapid (a few minutes) compared with dyes such as DASPMI (4-Di-1-ASP, D288), which may take 30 minutes or longer.14 Viewed through a fluorescein longpass optical filter (Table 23.12), fluorescence of the mitochondria of cells stained by rhodamine 123 appears yellow-green. Viewed through a tetramethylrhodamine longpass optical filter, however, these same mitochondria appear red. Unlike the lipophilic rhodamine and carbocyanine dyes, rhodamine 123 apparently does not stain the endoplasmic reticulum.

Rhodamine 123 has been used with a variety of cell types such as presynaptic nerve terminals,57 live bacteria,58,59 plants 60,61 and human spermatozoa.62 Using flow cytometry, researchers employed rhodamine 123 to sort respiratory-deficient yeast cells 63,64 and to isolate those lymphocytes that are responsive to mitogen stimulation.65 Rhodamine 123 has also been used to study:

• Apoptosis 52,66

• Axoplasmic transport of mitochondria 67

• Bacterial viability and vitality 58

• Mitochondrial enzymatic activities 68,69

• Mitochondrial transmembrane potential and other membrane activities 15,60,70�73

• Multidrug resistance 74�81 (Section 15.6)

• Mycobacterial drug susceptibility 82,83

• Oocyte maturation 84

Although rhodamine 123 is usually not retained by cells when they are washed, a variety of human carcinoma cell lines (but not sarcomas or leukemic cells) retain the dye for unusually long periods 85 (>24 hours), making rhodamine 123 a potential anticancer agent for photodynamic therapy.86�91 Rhodamine 123 is known to be preferentially taken up and retained by mitochondria of carcinoma cells 92 and to inhibit their proliferation;93,94 cardiac muscle cells also retain rhodamine 123 for days.95

Rosamines and Other Rhodamine Derivatives, Including TMRM and TMRE

Other mitochondrion-selective dyes include tetramethylrosamine (T639, Figure 12.23), whose fluorescence contrasts well with that of fluorescein for multicolor applications, and rhodamine 6G 89,96�98 (R634, Figure 12.24), which has an absorption maximum between that of rhodamine 123 and tetramethylrosamine. Tetramethylrosamine and rhodamine 6G have both been used to examine the efficiency of P-glycoprotein�mediated exclusion from multidrug-resistant cells 74 (Section 15.6). Rhodamine 6G has been employed to study microvascular reperfusion injury 99 and the stimulation and inhibition of F1 -ATPase from the thermophilic bacterium PS3.100

At low concentrations, certain lipophilic rhodamine dyes selectively stain mitochondria in live cells.101 Molecular Probes' researchers have observed that low concentrations of the hexyl ester of rhodamine B (R 6, R648MP) accumulate selectively in mitochondria (Figure 12.25) and appear to be relatively nontoxic. We have included this probe in our Yeast Mitochondrial Stain Sampler Kit (Y7530, see below for description). At higher concentrations, rhodamine B hexyl ester and rhodamine 6G stain the endoplasmic reticulum of animal cells 101 (Section 12.4).

The accumulation of tetramethylrhodamine methyl and ethyl esters (TMRM, T668; TMRE, T669) in mitochondria and the endoplasmic reticulum has also been shown to be driven by their membrane potential 102,103 (Section 22.3). Moreover, because of their reduced hydrophobic character, these probes exhibit potential-independent binding to cells that is 10 to 20 times lower than that seen with rhodamine 6G.104 Tetramethylrhodamine ethyl ester has been described as one of the best fluorescent dyes for dynamic and in situ quantitative measurements ― better than rhodamine 123 ― because it is rapidly and reversibly taken up by live cells.105�107 TMRM and TMRE have been used to measure mitochondrial depolarization related to cytosolic Ca2+ transients 108 and to image time-dependent mitochondrial membrane potentials.106 A high-throughput assay utilizes TMRE and our low-affinity Ca2+ indicator fluo-5N AM (F14204, Section 19.3) to screen inhibitors of the opening of the mitochondrial transition pore.109 Researchers have also taken advantage of the red shift exhibited by TMRM, TMRE and rhodamine 123 upon membrane potential�driven mitochondrial uptake to develop a ratiometric method for quantitating membrane potential.70

Reduced Rhodamines and Rosamines

Inside live cells, the colorless dihydrorhodamines and dihydrotetramethylrosamine are oxidized to fluorescent products that stain mitochondria.110 However, the oxidation may occur in organelles other than the mitochondria. Dihydrorhodamine 123 (D632, D23806; Figure 12.26) reacts with hydrogen peroxide in the presence of peroxidases,111 iron or cytochrome c 112 to form rhodamine 123. This reduced rhodamine has been used to monitor reactive oxygen intermediates in rat mast cells 113 and to measure hydrogen peroxide in endothelial cells.112 Dihydrorhodamine 6G (D633, Figure 12.27) is another reduced rhodamine that has been shown to be taken up and oxidized by live cells.114�116 Chloromethyl derivatives of reduced rosamines (MitoTracker Orange CM-H2 TMRos, M7511; MitoTracker Red CM-H2 XRos, M7513), which can be fixed in cells by aldehyde-based fixatives, have been described above. The acetoxymethyl (AM) ester of dihydrorhod-2, which is prepared by chemical reduction of the calcium indicator rhod-2 AM (R1244, R1245MP; Section 19.3) has been extensively used to measure the relatively slow changes in intramitochondrial Ca2+ (Figure 19.33, Figure 19.39).

Other Mitochondrion-Selective Probes

Carbocyanines

Most carbocyanine dyes with short (C1 �C6 ) alkyl chains (Section 22.3) stain mitochondria of live cells when used at low concentrations (~0.5 µM or ~0.1 µg/mL); those with pentyl or hexyl substituents also stain the endoplasmic reticulum when used at higher concentrations (~5�50 µM or ~1�10 µg/mL). DiOC6 (3) (D273) stains mitochondria in live yeast 21,117�119 and other eukaryotic cells,98,120 as well as sarcoplasmic reticulum in beating heart cells.121 It has also been used to demonstrate mitochondria moving along microtubules.23 Photolysis of mitochondrion- or endoplasmic reticulum�bound DiOC6 (3) specifically destroys the microtubules of cells without affecting actin stress fibers, producing a highly localized inhibition of intracellular organelle motility.122 We have included DiIC1 (5) and DiOC2 (3) in two of our MitoProbe Assay Kits for flow cytometry (M34151, M34150; Section 22.3). Several other potential-sensitive carbocyanine probes described in Section 22.3 also stain mitochondria in live cultured cells.98

The carbocyanine DiOC7 (3) (D378), which exhibits spectra similar to those of fluorescein, is a versatile dye that has been reported to be a sensitive probe for mitochondria in plant cells.123 Its other uses include:

• Distinguishing cycling and noncycling fibroblasts 124 and viable and nonviable bacteria 125
• Following the reorganization of the endoplasmic reticulum during fertilization in the ascidian egg 126
• Identifying functional vasculature in murine tumors 127,128
• Studying multidrug resistance 129 (Section 15.6)
• Visualizing the detailed morphology of neurites of Alzheimer's disease neurons 130

Styryl Dyes

The styryl dyes DASPMI (4-Di-1-ASP, D288) and DASPEI (D426) can be used to stain mitochondria in live cells.14 These dyes have large fluorescence Stokes shifts and are taken up relatively slowly as a function of membrane potential. The kinetics of mitochondrial staining with styrylpyridinium dyes has been investigated using the concentration jump method.131 DASPMI and DASPEI have been shown to be useful for:

• Determining the distribution of mitochondria in yeast mutants 63
• Long-term imaging of live mammalian nerve cells and their connections 132�134
• Monitoring the metabolic state of Pneumocystis carinii mitochondria 31
• Screening aberrant mitochondrial distribution and morphology in yeast 135

Nonyl Acridine Orange

Nonyl acridine orange (A1372) is well retained in the mitochondria of live HeLa cells for up to 10 days, making it a useful probe for following mitochondria during isolation and after cell fusion.136�138 The mitochondrial uptake of this metachromatic dye is reported not to depend on membrane potential. It is toxic at high concentrations 139 and apparently binds to cardiolipin in all mitochondria, regardless of their energetic state.140�143 This derivative has been used to analyze mitochondria by flow cytometry,144 to characterize multidrug resistance 145 (Section 15.6) and to measure changes in mitochondrial mass during apoptosis in rat thymocytes.52

Carboxy SNARF-1 pH Indicator

A special cell-loading technique permits ratiometric measurement of intramitochondrial pH with our SNARF dyes. Cell loading with 10 µM 5-(and 6-)carboxy SNARF-1, acetoxymethyl ester, acetate (C1271, C1272; Section 20.2), followed by 4 hours of incubation at room temperature leads to highly selective localization of the carboxy SNARF-1 dye in mitochondria (Figure 20.13), where it responds to changes in mitochondrial pH.146

CoroNa Red Chloride

As shown by colocalization with MitoTracker Green FM, the CoroNa Red Na+ indicator (C24430, C24431; Section 21.1) spontaneously localizes in the mitochondria (Figure 21.14) and may be useful for measuring intramitochondrial Na+ transients.

Lucigenin

The well-known chemiluminescent probe lucigenin (L6868) accumulates in mitochondria of alveolar macrophages.147 Relatively high concentrations of the dye (~1