Oxonol dyes

The condensation of a thiazolium with an oxonol dye in a basic medium is another example of the combination of electrophilic and nucleophilic reagents (Scheme 55). With a nonopening ring, the obtained neutrodimethine cyanine is not mesosubstimted (68). 

The cleavage of thiazolopentamethine cyanine and also neocyanine results in a tetramethine neutrocyanine together with neutrodimethine cyanine (26). 2-Methylthiazolium reacts with a trimethine oxonol dye and gives a neutrotetramethine dye (Scheme 56) (26). 

Slow-response probes (response times greater than milliseconds) cationic car-bocyanine and rhodamine dyes and anionic oxonol dyes... 

Fig. 3.2 (See also plate section.) Three of the concomitant polymorphs of the cyanine oxonol dyes 3-XVI and 3-XVII. Gold (by reflection otherwise red by transmission) and red forms mentioned in the text are easily distinguishable. The third form is a purple one, normally diamond shaped as on the middle right, but many of these crystals are undergoing conversion, as indicated by varying degrees of mottled surfaces. (From Bernstein et al. 1999, with permission.)...

Arreola, J. et al. (1995) Volume-activated chioride channels in HL-60 celis Potent inhibition by an oxonol dye. Am.J. Physiol. Cel Physiol.. 269. C1063-C1072. Greenwood, I.A. er al. (1995) Comparison of the effects of fenamates on Ca-activated chloride and potassium currents in rabbit portal vein smooth muscle cells. Br. J. Pharmacol.. II6,2939-2948. 

A schematic representation of a FRET-based voltage sensor assay is shown in Fig. 13. The assay principle was first published [105] and then further improved [106] by Gonzalez and Tsien, then commercialized [107], and is now available from Panvera [108]. The FRET donor is a coumarin dye, which is covalently linked to a phosphoHpid. The acceptor is a highly fluorescent, membrane-soluble anionic ox-onol dye. When the cell membrane is loaded with the dyes, the phospholipid anchors the coumarin donor to the outside of the cell, whereas the oxonol dye is accumulated in the ceU membrane. The distribution of the anionic oxonol in the membrane depends on the polarity of the membrane potential if the oxonol dye is located on the extracellular side of the membrane in close proximity to the coumarin donor, FRET occurs and the emission is mostly at 580 nm. If the polarity changes, the oxonol rapidly translocates to the intracellular side of the membrane, too far from the coumarin donor for FRET, and the emission is mostly at 460 nm. 

Plasma membrane potential of animal cells The membrane potential of whole cells is more difficult to assess than that of isolated organelles with optical indicators because cells contain many sub-ccllular compartments, and it is necessary to isolate the response of the plasma membrane from that of any other cell membrane. For example, the intense staining of mitochondria by cyanine dyes (7). which are membrane-permeant cations, means that if you choose a cyanine dye, or other lipophilic cation, lo measure plasma membrane potential it is important to establish conditions where the mitochondrial potential is disabled. If an anionic dye is chosen, this problem is overcome but there is, then, very little entry of dye into the cells unless the dye is itself reasonably lipophilic. Thus, for studies of whole cells, we employ an oxonol dye with a phenyl substituent. The procedures fijr mc.isuring plasma membrane potential with this dye, oxonol-V (31), are illustrated in R,giirf. j and Protocol 2. 

There is a danger that the lipophilic valinomycin/K complex may precipitate lipophilic anions such as the oxonol dyes and it is advisable to check on the calibration described above with another ionophore. The uncoupling agent FCCP is useftil in this respect as it selectively increases the H permeability of membranes. Tlic experimental protocol for measuring the potential using FCCP... 

Russell, J. T. Beeler, T. Martonosi, A. Optical probe responses on sarcoplasmic reticulum merocyanine and oxonol dyes. J. Biol Chem. 1979, 254, 2047-2052. 

Morimoto, T Sakamoto, K. Sade, H. Ohya, S. Muraki, K. Imaizumi, Y. Voltage-sensitive oxonol dyes are novel large-conductance Ca -activated K" " channel activators selective for 3 1 and 3 4 but not for 3 2 subunits. Mol Pharmacol 2007, 71, 1075-1088. 

Molotkovskii, Yu. G. Yakovleva, G. A. Oxonol dye diBa-C4-(5) as a fluorescent probe for membrane potential in chloroplasts and its interaction with valinomycin. Photosynthetica 1985, 19, 493-499. 

Clarke, R. J. Apell, H. J. A stopped-flow kinetic study of the interaction of potential-sensitive oxonol dyes with lipid vesicles. Biophys. Chem. 1989, 34, 225-237. 

Bashford, C. L. Alder, G. M. Gray, M. A. Micklem, K. J. Taylor, C. C. Turek, P. J. Pasternak, C. A. Oxonol dyes as monitors of membrane potential the effect of viruses and toxins on the plasma membrane potential of animal cells in monolayer culture and in suspension. J. Cell. Physiol. 1985, 123, 326-336. 

Bashford, C. L. Chance, B. Prince, R. C. Oxonol dyes as monitors of membrane potential their behavior in photosynthetic bacteria. Biochim. Biophys. Acta, Bioenerg. 1979, 545, 46-57. 

Waggoner, A. S. Wang, C. H. Tolies, R. L. Mechanism of potential-dependent light absorption changes of lipid bilayer membranes in the presence of cyanine and oxonol dyes. J. Membr. Biol. 1977,33, 109-140. 

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