The hydrophobic fluorescence dye 10-n-nonyl-acridinium-orange-chloride, NAO, stains specifically the mitochondria of living HeLa-cells. A dye concentration of 1 X 10(-8) M is sufficient for vital staining and at 5 X 10(-7) M an incubation time less than 1 min is enough to generate the bright green fluorescence of the mitochondria. The retention of NAO by the mitochondria is longer than 7 days. The dye accumulation is not affected by the ionophores valinomycin, nigericin, gramicidin, the uncoupling agents DNP, CCCP or by ouabain. In contrast to Rh 123 the trans-membrane potential is not the driving force of the NAO accumulation. We assume that NAO is bound to the hydrophobic lipids and proteins in the mitochondrial membranes by hydrophobic interaction. With valinomycin, 500 ng/ml, 10 min, the mitochondria in HeLa-cells swell. Now it is possible to observe some details in the enlarged mitochondria by light microscopy. After vital staining with NAO, 5 X 10(-7) M, 10 min, the periphery of the swollen mitochondria shows an intense green fluorescence, the inner part is dark. Obviously the dye is bound to the membranes. By electron microscopy it can be shown that the valinomycin treated and NAO stained mitochondria have outer and inner membranes and cristae. They differ from untreated mitochondria mainly in the size. After incubation of the HeLa-cells with relatively high NAO concentrations, 5 X 10(-6) M, 10 min, the mitochondria show a weak orange fluorescence. It is generated by the dimers D of NAO. Therefore the dye concentration in the mitochondrial membranes is locally very high and causes dye dimerisation. The weak orange fluorescence is instable and disappears within a few seconds. Instead we observe a green fluorescence with growing intensity that is generated by the monomers M of NAO. The intensity has its maximum value after a few seconds. Using low NAO concentrations for incubation, 1 X 10(-7) M, 10 min, we observe only the green fluorescence with increasing intensity. In this case the orange fluorescence is too weak for observation (concentration quenching). It can be shown by experiments and quantum mechanics that the orange fluorescence is assigned to an optical forbidden, the green fluorescence to an allowed electronic transition of D or M respectively. Our results indicate a dissoziation of D in 2 M by irradiation of the mitochondria under the fluorescence microscope.(ABSTRACT TRUNCATED AT 400 WORDS)

Es wird ein Verfahren beschrieben, das es gestattet, die Konzentration von Radikallösungen ESR‐spektroskopisch durch Vergleich mit einem DPPH‐Standard zu bestimmen. Die Signale von Probe und Standard werden mit einem ESR‐Spektrometer mit Feldmodulation gemessen und automatisch auf Lochkarten registriert. Anschließend werden sie mit einem Computerprogramm zweimal integriert und auf das Signal eines sekundären Rubin‐Standards normiert, der fest im Resonator eingebaut ist. Aus den normierten, integralen Absorptionen von Probe und primärem Standard läßt sich die Radikalkonzentration der untersuchten Substanz ermitteln. Zur Bestimmung der Fehlergrenzen des Verfahrens wurde die Konzentrations‐ und Temperaturabhängigkeit der Radikalkonzentration cR von DPPH‐Proben innerhalb weiter Grenzen untersucht. Die Standardabweichung war kleiner als ± 10%. Die Methode wurde dazu verwendet, die Konzentrations‐ und Temperaturabhängigkeit des Radikalgehalts γ von Proben aus Tri‐p‐biphenylylmethyl (TBM) in Toluol bzw. Benzol zu bestimmen. Die Darstellung der Radikallösungen erfolgte in einer abgeschmolzenen Apparatur unter Stickstoff durch Umsetzung von Tri‐p‐biphenylyl‐methyl‐chlorid mit Silberpulver. Die Einwaagekonzentration des Radikals c0 wurde aus der Menge des eingesetzten Chlorids und seinem Enthalogenierungsgrad ermittelt. Der Radikalgehalt der Probe γ = cR/c0 ist – in übereinstimmung mit älteren Messungen auf der magnetischen Waage – innerhalb der Fehlergrenzen temperaturunabhängig. Daraus folgt, daß TBM in Lösung nicht assoziiert ist und als monomeres Radikal vorliegt. Der Radikalgehalt aller ESR‐spektroskopisch untersuchten Proben war γ < 1. Das Radikaldefizit kann nicht auf Assoziation, Lösungsmitteleinschlüsse in der Probe oder auf anomalen Diamagnetismus des Radikals (Selwood‐Effekt) zurückgeführt werden. Der Selwood‐Effekt ist auszuschließen, da ESR‐spektroskopisch nur die paramagnetische Suszeptibilität erfaßt wird. Wir nehmen an, daß Sekundärreaktionen für das Radikaldefizit verantwortlich sind.

Lipophilic cationic fluorescent dyes (D) specifically stain the mitochondria of living cells. A perfusion chamber for cell cultures is described, which can be used to determine the kinetics of vital staining of the mitochondria of single selected cells in situ. In these experiments styrylpyridinium dyes and cultures of HeLa cells were used. The dyes differ strongly in their lipophilic properties; Rm values and the partition coefficients Po/w between n-octanol (o) and water (w) were determined in order to characterize their lipophilicity. In the thermostat-regulated chamber the concentration of the dye CD can be increased from CD = 0 to CD > 0 within a few seconds (concentration jump). Thus, the time t = 0 for the beginning of the vital staining and the dye concentration in the cell medium during the staining experiment, CD = const., are unambiguously defined. The concentration of the dye, Cb, which is bound to the mitochondria (b), is proportional to the intensity of the fluorescence Ib. On the other hand, the free dye molecules (f) in the aqueous medium exhibit practically no fluorescence, I(f) << Ib. The intensity of the fluorescence I = Ib was measured as a function of time t; the measured values were corrected for photobleaching. The fluorescence intensity I(t) at first increases linearly with t and reaches a saturation value for t-->infinity. In the linear range of I(t) the flow J(o) = (dI/dt)o of the dye into the cell depends strongly on the dye concentration and increases linearly with CD. The concentration range CD = 10(-9)-10(-5) M at 37 degrees C was investigated. From the linear correlation between J(o) and CD it follows that the kinetics of the vital staining of mitochondria is controlled by diffusion. At t = 0 the flow of the xenobiotic agent through the cell membrane determines the rate of staining. The slope dJ(o)/dCD of the plot J(o) vs CD describes the efficiency of dye accumulation at the mitochondria and strongly increases with increasing lipophilicity of the dye molecules. Thus lipophilic dyes pass through the cell membrane more easily than less lipophilic molecules.

Several investigators have described the ultrastructural changes that occur in the mitochondria of cells in tissue cultures after treatment with the drug ethidium bromide (E). The mitochondria swell and the cristae become greatly altered and finally disappear; in the cristae-free region of the matrix electron-dense granules can be observed. It has been assumed that intercalation of E between the base pairs of the mitochondrial DNA induces the formation of the granular inclusions. To investigate whether intercalation is really the initial step in the generation of dense granules inside the matrix, we performed a comparative incubation study of HeLa-cell mitochondria in situ using three closely related dyes (D), i.e., E, tetramethylethidium bromide (TME) and betaine B (B). They strongly differ with regard to their affinity for DNA and their ability to cross membranes. E was used as a reference dye. TME does not intercalate, but is externally bound to DNA only weakly. The neutral B is not bound at all, but can cross membranes more easily than the cation E. Moreover, in aqueous solutions at pH approximately equal to 7.0, B is in equilibrium with its protonated cation BH. BH and E have almost equal affinities for DNA. Therefore B may quickly pass the inner mitochondrial membranes and the cristae, and should then be bound inside the matrix, thus forming a BH-DNA complex. On the assumption that intercalation is necessary for the generation of intramitochondrial electron-dense bodies, we predicted that BH/B should be more efficient than E, while TME should be relatively ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

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10-n-Alkyl-acridine-orange-chlorides (alkyl-AOs) are excellent dyes for fluorescence staining of mitochondria in living cells. The thermodynamic and spectroscopic properties of the series alkyl = methyl to nonyl have been investigated. The dyes form dimers in aqueous solution. The dimerisation is mainly a consequence of the hydrophobic interaction. The dissociation constant K respectively association constant K-1 of the dimers describes the hydrophobic interaction and therefore the hydrophobic properties of the dye cations. The dissociation constant K = K0 at the standard temperature T = 298 K has been determined spectroscopically in aqueous solution. It depends on the length of the alkyl residue n-CmH2m + 1 (m = 1 - 9) (Table 2). In addition the standard dissociation enthalpies (energies) delta H0 and dissociation entropies delta S0 have been determined from the temperature dependence of K (Table 2). With increasing chain length m the thermodynamic parameters K0, delta H0, delta S0 decrease. Therefore with growing m the dimers are stabilized. This stabilization is an entropic effect which is diminished by the energetic effect. The change of the thermodynamic parameters with m is in agreement with the concept of hydrophobic interaction and the stabilization of water structure in the surroundings of hydrophobic residues. As one would expect nonyl-AO is the most hydrophobic dye of the series. As an example the spectroscopic properties of nonyl-AO have been determined. We measured the absorption, luminescence and polarization spectra in rigid ethanol at 77 K. Under these conditions alkyl-AOs associate like dyes in Water at room temperature. The spectra depend on the concentration of the solution. In very dilute solution we observe mainly the spectra of the monomers M, in concentrated solution the spectra of the dimers D. The spectra of M and D are characteristically different. The monomers have one long wave length absorption M1 = 20.000 cm-1 with resonance fluorescence. In addition there is a long living phosphorescence at 16.600 cm-1. Its polarization is nearly perpendicular to the plane of the AO residue. The dimers have two long wave length absorption bands D1 = 18.700 and D2 = 21.200 cm-1 with very different intensities. D1 has very low intensity and is forbitten, D2 is allowed. D1 shows fluorescence. Phosphorescence has not been observed. D1, D2 and also M1 are polarized in the plane of the AO residue. At short wave length absorption and polarization spectra are very similar. From the spectra we constructed the energy level diagram of M and D (Fig. 9). The first excited state of M splits in D in two levels. The level splitting and the transition i

The fluorescent staining of mitochondria in living cells with new acridine dyes is reported. The fluorescent dyes used are derivatives of acridine orange (AO) and of 3-amino-6-methoxyacridine (AMA) with various residues in 9- or 10-position (Scheme 1). They are either permanent cationic dyes or cations which are formed by protonation in the culture medium. HeLa cells and mouse fibroblasts (LM cells) have been used for our staining experiments. On favourable conditions we succeeded in staining the mitochondria not only orthochromatically but also metachromatically. Photodynamical effects which have been observed during the exposure of the stained cells in the fluorescence microscope are described. The residues in 9- or 10-position favour the dye accumulation in the mitochondria. Vital staining with the basic compounds AO and AMA however leads to the formation of metachromatically stained lysosomes in the orthochromatically stained cytoplasm. The dye 3-amino-6-methoxy-9-(2-hydroxyethyl)acridine stains the nucleus of living cells.

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