A cyanine dye distinguishes between cycling and non-cycling fibroblasts

Single-cell image analysis to assess ABC-transporter-mediated efflux in highly purified hematopoietic progenitors

BACKGROUND

Normal and malignant hematopoietic stem cells are characterized by their capacity to actively extrude fluorescent dyes. The contribution of different ATP-binding cassette (ABC) transporters to this phenomenon is largely unknown due to the small stem cell numbers limiting the use of standard methods to assess functional efflux.

METHODS

We used epifluorescence microscopy (EFM) in combination with single-cell image analysis to study ABC-transporter-mediated efflux in highly purified, viable, CD34+CD38- cells sorted on an adhesive biolayer. P-glycoprotein and multidrug-resistant protein (MRP)-mediated efflux were quantitated using fluorescent substrates (rhodamine-123 and calcein acetoxymethyl ester [calcein-AM]) and specific inhibitors (verapamil and probenecid, respectively).

RESULTS

The feasibility, sensitivity, and reproducibility of rhodamine-123 efflux quantitation using single-cell EFM was shown in cell lines and compared with standard flow cytometric assessment. P-glycoprotein-mediated transport was higher in CD34+CD38- cells than in more differentiated progenitors (mean efflux index = 2.24 +/- 0.35 and 1.14 +/- 0.11, respectively; P = 0.01). P-glycoprotein-mediated transport was the main determinant of the rhodamine "dull" phenotype of these cells. In addition, significant MRP-mediated efflux was demonstrated in CD34+CD38- and CD38+ cells (mean efflux index = 1.42 +/- 0.19 and 1.28 +/- 0.18, respectively).

CONCLUSION

The described method is a valuable tool for assessing ABC-transporter-mediated efflux in highly purified single cells. Both P-glycoprotein and MRP-mediated efflux are present in human CD34+CD38- hematopoietic stem cells.

Oligonucleotide-conjugated thiazole orange probes as "light-up" probes for messenger ribonucleic acid molecules in living cells

"Light-up" probes, icosa-alpha-thymidylate-thiazole orange conjugates, for the in situ time-resolved detection of messenger ribonucleic acid (mRNA) in living cells are evaluated. Upon annealing with polyA in aqueous solutions, the icosa-alpha-thymidylate-thiazole orange conjugates were shown to be up to 15 times more fluorescent. Microinjection of these probes into adherent fibroblasts resulted in high yields of hybridization and fluorescent signals. Incubation of cells in the presence of these probes resulted in facile internalization of the probe and similar painting of the messenger RNA in the nuclear and cytosolic regions.

Dynamics of mitochondria in living cells: shape changes, dislocations, fusion, and fission of mitochondria

Mitochondria are semi-autonomous organelles which are endowed with the ability to change their shape (e.g., by elongation, shortening, branching, buckling, swelling) and their location inside a living cell. In addition they may fuse or divide. These dynamics are discussed. Dislocation of mitochondria may result from their interaction with elements of the cytoskeleton, with microtubules in particular, and from processes intrinsic to the mitochondria themselves. Morphological criteria and differences in the fate of some mitochondria argue for the presence of more than one mitochondrial population in some animal cells. Whether these reflect genetic differences remains obscure. Emphasis is laid on the methods for visualizing mitochondria in cells and following their behaviour. Fluorescence methods provide unique possibilities because of their high resolving power and because some of the mitochondria-specific fluorochromes can be used to reveal the membrane potential. Fusion and fission often occur in short time intervals within the same group of mitochondria. At sites of fusion of two mitochondria material of the inner membrane, the matrix compartment seems to accumulate. The original arrangement of the fusion partners is maintained for some minutes. Fission is a dynamic event which, like fusion, in most cases observed in vertebrate cell cultures is not a straight forward process but rather requires several "trials" until the division finally occurs. Regarding fusion and fission hitherto unpublished phase contrast micrographs, and electron micrographs have been included.

Mitochondrial dysfunction in yeast expressing the cytoplasmic male sterility T-urf13 gene from maize: analysis at the population and individual cell level

The urf13TW gene, which is derived from the mitochondrial T-urf13 gene responsible for Texas cytoplasmic male sterility in maize, was expressed in Saccharomyces cerevisiae by targeting its translation product into mitochondria. Analysis by oxygraphy at the population level revealed that in the presence of methomyl the oxygen uptake of intact yeast cells carrying the targeted protein is strongly stimulated only with ethanol as respiratory substrate and not with glycerol, lactate, pyruvate, or acetate. When malate is the substrate oxidized by isolated mitochondria, interaction between the targeted protein and methomyl results in significant inhibition of oxygen uptake. This inhibition is eliminated and oxygen uptake is stimulated by subsequent addition of NAD+. Using 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)] as probe, interactive laser scanning and flow cytometry, which permit analysis at the individual cell level, demonstrated that specific staining of the mitochondrial compartment is obtained and that DiOC6(3) fluorescence serves as a measure of the membrane potential. Finally, it was shown that, as in T cytoplasm maize mitochondria, HmT toxin and methomyl dissipate the membrane potential of yeast mitochondria that carry the foreign protein. Furthermore, the results suggest that the HmT toxin and methomyl response is related to the plasmid copy number per cell and that the deleterious effect induced by HmT toxin is stronger than that of methomyl.

Simultaneous use of rhodamine 123, phycoerythrin, Texas red, and allophycocyanin for the isolation of human hematopoietic progenitor cells

The supravital, mitochondrial specific dye Rhodamine 123 (R123) was used in conjunction with three monoclonal antibodies to isolate a population of human bone marrow (BM) cells enriched for hematopoietic progenitor cells. BM cells stained with phycoerythrin-HLA-DR, Texas red-CD34, allophycocyanin-CD15, and R123 were fractionated using four-color immunofluorescence cell sorting. Cells expressing CD34 but not HLA-DR and CD15 (CD34+ HLA-DR- CD15-) were subdivided according to their reactivity with R123 into quiescent, R123 dull (R+) or cycling, R123 bright (R++) subpopulations. Morphological analysis and hematopoietic progenitor cell assays indicated that CD34+ HLA-DR- CD15- R+ cells contained larger numbers of blast cells and colony forming units than CD34+ HLA-DR- CD15- R++ cells. The flow cytometer settings used to accommodate the detection of the R123 fluorescence in combination with that of three other fluorochromes are described.

Retention of the mitochondrial probe rhodamine 123 in normal lymphocytes and leukemic cells in relation to the cell cycle

The cationic fluorochrome rhodamine 123 (R123) is specifically taken up by mitochondria of live cells where it is retained due to the mitochondrial transmembrane potential. After pulse exposure of human normal quiescent or proliferating lymphocytes, human lymphocytic leukemic MOLT cells, and mice leukemic L1210 cells to 10 micrograms/ml of R123, the dye release was studied using flow cytometry. Two distinct phases of R123 release, each following first-order kinetics, were apparent; the half-time of retention for the rapidly and slowly released fractions of R123 was 0.8-1.1 and 2.8-4.2 h, respectively. Simultaneous supravital cell staining with R123 and Hoechst 33342 made it possible to correlate retention of R123 with cell position in the cell cycle. No significant differences were observed in the rate of R123 release from cells in G1 vs S or vs G2 + M phases of the cycle. The data rule out a possibility that the release of R123 is due to periodic depolarization of the mitochondria in the cell as may be postulated by cell cycle models that assume a transient passage of cells through resting phase following division. The observed similar rates of R123 release regardless of cell type or cell cycle phase suggest that the factors affecting the exchange are similar in normal lymphocytes vs leukemic cells and unrelated to cell proliferation rate or phase of the cell cycle. Two distinct rates of R123 release indicate the presence of two kinds of binding sites differing in affinity to the dye.

Use of nonyl acridine orange and rhodamine 123 to follow biosynthesis and functional assembly of mitochondrial membrane during L1210 cell cycle

Specific mitochondrial incorporation of 10 N-nonyl acridine orange (NAO) is demonstrated by subcellular fractionation of rat hepatocytes. Moreover, comparative studies with NAO and rhodamine 123 (Rh 123) prove that acridine orange-derivative uptake is independent of transmembrane mitochondrial potential, a property allowing its utilization for the assessment of mitochondrial membrane mass modifications under various physiological states. Using NAO and Rh 123, we have respectively followed the biosynthesis of mitochondrial membrane and its assembly under a functional state during the L1210 cell cycle. Their evolution occurs in two stages according to a well-defined sequential order. Mitochondrial biogenesis, as revealed by NAO incorporation, occurs essentially in the G1 phase (probably mitochondrion enlargement) but also starts in late S phase (probably mitochondrion division). The increased amount of functional mitochondrial membrane, monitored by Rh 123 uptake, is emphasized in late G1 (prerequisite to DNA synthesis) and during G2M phases (prerequisite to mitosis). This alternative succession of phases displays the existence of a time-lag between the biosynthesis of mitochondrial membrane and its functional organization. Such an analysis confirms the potential of the NAO probe to evaluate mitochondrial membrane mass changes in various biological fields.

Simultaneous imaging of cell and mitochondrial membrane potentials

The distribution of charged membrane-permeable molecular probes between intracellular organelles, the cytoplasm, and the outside medium is governed by the relative membrane electrical potentials of these regions through coupled equilibria described by the Nernst equation. A series of highly fluorescent cationic dyes of low membrane binding and toxicity (Ehrenberg, B., V. Montana, M.-D. Wei, J. P. Wuskell, and L. M. Loew, 1988. Biophys. J. 53:785-794) allows the monitoring of these equilibria through digital imaging video microscopy. We employ this combination of technologies to assess, simultaneously, the membrane potentials of cells and of their organelles in situ. We describe the methodology and optimal conditions for such measurements, and apply the technique to concomitantly follow, with good time resolution, the mitochondrial and plasma membrane potentials in several cultured cell lines. The time course of variations induced by chemical agents (ionophores, uncouplers, electron transport, and energy transfer inhibitors) in either or both these potentials is easily quantitated, and in accordance with mechanistic expectations. The methodology should therefore be applicable to the study of more subtle and specific, biologically induced potential changes in cells.

Photosensitization of human glioma cells by chalcogenapyrylium dyes

Chalcogenapyrylium (CP) dyes which are specifically activated by red and near infrared light (600-900 nm) were examined as potential photosensitizers for photochemotherapy of malignant gliomas. Eleven CP dyes of varying chemical structure and redox potential were evaluated for selective toxicity against glioma and normal skin fibroblast cell cultures both before and after light activation. Eight of eleven CP dyes exhibited differential toxicity to tumor over fibroblast cells at dye concentrations of 1.0 microM. Dose dependent toxicity was seen both in the dark and after laser light activation. The toxicity of two of the CP dyes was significantly enhanced by photoactivation with 800 nm light. The CP dyes that absorb light maximally between 775 and 850 nm, in the range of excellent light penetration through brain, appear to be promising candidates as photosensitizers for treating malignant brain tumors.

Low Ca2+-sensitive maxi-K+ channels in human cultured fibroblasts

The patch clamp technique was used to reveal single channel activity in the membrane of human cultured fibroblasts. The most frequently detected ion channel type was a Ca2+-dependent K+ channel with a conductance of 287 +/- 38 pS in symmetrical 130 mM KCl. The channel showed a peculiar low Ca2+-sensitivity compared to that of similar channels in other preparations. In fact micromolar values of internal Ca2+ were not effective in the channel activation, except at high depolarizing membrane potentials. The activity was highly increased only when the channel was exposed to relatively high internal Ca2+ concentrations (0.2-2.0 mM).

Luminescence spectroscopic approaches in studying cell surface dynamics

The major elements of membranes, such as proteins, lipids and polysaccharides, are in dynamic interaction with each other (Albertset al.1983). Protein diffusion in the lipid matrix of the membrane, the lipid diffusion and dynamic domain formation below and above their transition temperature from gel to fluid state, have many functional implications. This type of behaviour of membranes is often summarized in one frequently used word membrane fluidity (coined by Shinitzky & Henkart, 1979). The dynamic behaviour of the cell membrane includes rotational, translational and segmental movements of membrane elements (or their domain-like associations) in the plane of, and perpendicular to the membrane. The ever changing proximity relationships form a dynamic pattern of lipids, proteins and saccharide moieties and are usually described as ‘cell-surface dynamics’ (Damjanovichet al.1981). The knowledge about the above defined behaviour originates from experiments performed mostly on cytoplasmic membranes of eukaryotic cells. Nevertheless numerous data are available also on the mitochondrial and nuclear membranes, as well as endo (sarco-)plasmic reticulum (Martonosi, 1982; Slater, 1981; Siekevitz, 1981).

Cells with marrow and spleen repopulating ability and forming spleen colonies on day 16, 12, and 8 are sequentially ordered on the basis of increasing rhodamine 123 retention

Mouse bone marrow cells (BMC) were subjected to countercurrent centrifugal elutriation and subsequently separated on the basis of light scatter and fluorescence intensity after being labeled with the supravital dye Rhodamine 123 (Rh-123). The sorted cells were then assayed for their in vivo spleen colony-forming ability (day -8, -12, and -16 CFU-S) and their ability to repopulate the bone marrow or spleen over a 13-day period with CFU-S-12, CFU-GM, or nucleated cells. Cells with marrow repopulating ability (MRA), as measured by the ability of the sorted cells to repopulate the marrow with secondary CFU-S-12 or CFU-GM, had low affinity for Rh-123. These cells showed minimal spleen colony-forming ability, and the ratio of MRA to CFU-S-12 in this preparation was 309. Cells with spleen repopulating ability (SRA), CFU-S-16, CFU-S-12, and CFU-S-8 retained increasing amounts of Rh-123, respectively, and CFU-S-8 were almost exclusively found among cells with high Rh-123 affinity. These cells also included about half of all day-12 CFU-S, and the ratio of MRA to day-12 CFU-S was 0. The results show that MRA cells, SRA cells, CFU-S-16, CFU-S-12, and CFU-S-8 can be sequentially ordered on the basis of increasing mitochondrial activity. The data also demonstrate for the first time, and without the application of negative selection by the use of cytostatic agents, that MRA cells are a separate class of primitive hemopoietic stem cells that fully meet the criteria of pre-CFU-S.

Potassium channels in human and avian fibroblasts

The cell-attached and excised inside-out patch-clamp techniques were used to study single-channel characteristics of potassium channels in cultured human and avian fibroblasts. Six different potassium channels were distinguished with conductances of 235 +/- 25, 190 +/- 57, 114 +/- 27, 77 +/- 14, 40 +/- 6 and 21 +/- 4 pS in symmetric 140 mM potassium solutions. The channels were separable by their conductances, ion-selectivities, voltage-sensitivities and kinetic properties. All six channels were found in both fully differentiated human skin fibroblasts and primary cultures of 72 h chick sclerotome. The largest channel (235 pS) had a steep bimodal voltage dependence, being open only around the resting membrane potential. It was imperfectly selective for potassium, having a relative sodium:potassium permeability of 0.3. The 190 pS channel was very potassium-selective, had an S-shaped voltage sensitivity and was calcium-dependent. The two intermediate-size channels (114 and 77 pS) had open probabilities of less than 0.5 under all of the conditions we used. They were not completely selective for potassium and were not voltage-sensitive. The two smallest channels (40 and 21 pS) were not well characterized. They both had open probabilities of less than 0.2 and showed no evidence of voltage-sensitivity. The 40 pS channel seemed highly potassium-selective. A suction stimulus was used to test all observed channels for mechanosensitivity but none of the six potassium channels was mechanosensitive. Another small channel, with very clear mechanical sensitivity, was seen on a few occasions; this channel has not yet been characterized.

Characterization of a carbocyanine derivative as a fluorescent penetration probe

The fluorescent carbocyanine dye 3,3-diheptyloxycarbocyanine [DiOC7(3)], originally described as a membrane potential probe, penetrates poorly into multicell spheroids. Since the dye is retained in the cells following spheroid disaggregation, cells can be selected from different depths within the spheroid using fluorescence-activated cell sorting. Characterization of the binding kinetics, stability, and toxicity of this probe were undertaken, and intercompared with Hoechst 33342. The optimum drug dose for achieving good separation of internal and external cells of spheroids is about tenfold lower than for Hoechst 33342, and like Hoechst, DiOC7(3) is toxic at concentrations at least tenfold higher than those required to produce a good gradient for cell separation. When cells are removed from the stain, cellular fluorescence decreases to half the initial intensity within 2 hours; however, unlike Hoechst, the carbocyanine dye does not transfer between cells.

Microscopic imaging of cells

The microworld was revealed to investigators through a glass bead or a hanging water droplet long before optics was understood. The cellular structure of plants was well resolved by such simple magnifying glasses, van Leeuwenhoek, the Dutch merchant and amateur microscopist, was the first to report to the English Royal Society his observations of bacteria with his single-lens microscope in 1665.

Five-parameter fluorescence imaging: wound healing of living Swiss 3T3 cells

Cellular functions involve the temporal and spatial interplay of ions, metabolites, macromolecules, and organelles. To define the mechanisms responsible for completing cellular functions, we used methods that can yield both temporal and spatial information on multiple physiological parameters and chemical components in the same cell. We demonstrated that the combined use of selected fluorescent probes, fluorescence microscopy, and imaging methods can yield information on at least five separate cellular parameters and components in the same living cell. Furthermore, the temporal and spatial dynamics of each of the parameters and/or components can be correlated with one or more of the others. Five parameters were investigated by spectrally isolating defined regions of the ultraviolet, visible, and near-infrared spectrum based on five distinct fluorescent probes. The parameters included nuclei (Hoechst 33342), mitochondria (diIC1-[5] ), endosomes (lissamine rhodamine B-dextran), actin (fluorescein), and the cell volume Cy7-dextran). Nonmotile, confluent Swiss 3T3 cells did not show any detectable polarity of cell shape, or distribution of nuclei, endosomes, or mitochondria. These cells also organized a large percentage of the actin into stress fibers. In contrast, cells migrating into an in vitro wound exhibited at least two stages of reorganization of organelles and cytoplasm. During the first 3 h after wounding, the cells along the edge of the wound assumed a polarized shape, carried the nuclei in the rear of the cells, excluded endosomes and mitochondria from the lamellipodia, and lost most of the highly organized stress fibers. The cell showed a dramatic change between 3 and 7 h after producing the wound. The cells became highly elongated and motile; both the endosomes and the mitochondria penetrated into the lamellipodia, while the nuclei remained in the rear and the actin remained in less organized structures. Defining the temporal and spatial dynamics and interplay of ions, contractile proteins, lipids, regulatory proteins, metabolites, and organelles should lead to an understanding of the molecular basis of cell migration, as well as other cellular functions.

Macrophage activation in rat models of inflammation and arthritis. Systemic activation precedes arthritis induction and progression

The association between the induction and progression of adjuvant-induced arthritis (AA) and the development of synovial and systemic macrophage activation was assessed by studying the temporal development of these parameters in a rat model. Rats with AA developed significant edema of the uninjected hind leg beginning 10 days post-adjuvant injection, with progressive increases in edema continuing through day 17. Several parameters of macrophage activation, including the enhanced ability to secrete interleukin-1 and prostaglandin E2, kill tumor cells, accumulate fluorescent cyanine dyes, emigrate into the peritoneal cavity and synovium, and express Ia antigen, as well as the decreased ability to secrete superoxide anion, were associated temporally with the development of the arthritic lesion. In addition to the temporal association between macrophage activation and development of arthritis, a positive correlation between macrophage activation and arthritis induction was seen with the use of synthetic adjuvants at arthritogenic and nonarthritogenic doses. These data taken together suggest that induction and progression of AA in rats is associated with both systemic (blood, spleen, and peritoneal cavity) and local (synovium) macrophage activation.

Cell cycle analysis using flow cytometry

This manuscript reviews the utility of flow cytometry for the study of cell proliferation. The applications of univariate DNA distribution analysis to cytokinetic studies of asynchronous and perturbed cell populations are discussed briefly. The newly developed technique for simultaneous flow cytometric measurement of cellular DNA content and amount of incorporated bromodeoxyuridine is discussed in more detail. The cytochemistry required for this analysis is reviewed as are its applications to: determination of the fractions of cells in the G1-, S- and G2 + M-phases of the cell cycle; determination of the G1-, S- and G2 + M phase durations and dispersions and growth fraction for asynchronous cells; detection of ara-C resistant cells present at low frequency in an otherwise sensitive population; and analysis of the cytokinetic response of a solid murine tumour to treatment in vivo with a cell cycle specific agent.

The effect of cytosine arabinoside upon mitochondrial staining kinetics in human hematopoietic cells

The measurement of time correlated intracellular mitochondrial staining with 3,3'-dipentyloxacarbocyanine [Di-O-C5(3)] appeared of interest to define the optimal staining conditions. Mitochondrial staining of lymphocytes, monocytes and granulocytes results in different fluorescence signals, related to the numbers of mitochondria, that are present in the cells of these various cell types. Alterations of Di-O-C(5)3 staining in a distinct cell type are due to changes in the physiological or functional state of the mitochondria. It appeared that such alterations occur in cells, which are cultured in the presence of cytosine arabinoside. The effect of cytotoxic drugs upon the mitochondrial membrane potential may be relevance for the understanding of the mechanism of action, exerted by cytotoxic drugs upon cell biology.

Multivariate analysis and list mode processing of murine hemopoietic subpopulations for cytokinetic studies

Multivariate analyses and list mode data processing were used to obtain cytokinetic information on flow cytometrically distinct hemopoietic subpopulations. In one application, viable, unfixed hemopoietic subpopulations were discriminated on the basis of cyanine dye fluorescence and orthogonal light scatter; Hoechst dye fluorescence was measured to determine the proliferative status of the subpopulations. In another application, ethanol-fixed mouse bone marrow cells were triply stained with Hoechst dye, rhodamine-conjugated wheat germ agglutinin (WGA), and a fluorescein-labeled monoclonal antibody against bromodeoxyuridine. In both of these studies, flow cytometric data for all three variables were acquired in list mode fashion, stored on magnetic tape, and processed by list mode software on a computer-based multivariable pulse-height analyzer. In the first application, subpopulations distinguished by cyanine dye intensity and light scatter appeared to be more related to cell lineage and cell size than proliferative status. In the second application, WGA affinity discriminated two subpopulations in mouse bone marrow S-phase cells in each subpopulation that actively incorporated bromodeoxyuridine (BrdUrd). List mode data processing obviates the need for routine electronic sorting of cells and thus facilitates characterization of discriminated subpopulations. In this regard, it is particularly useful for the study of flow cytometrically distinct, low frequency subpopulations.

Fluorescence digital imaging microscopy in cell biology

Developments in microscope, sensor, and image-processing technologies have led to integrated systems for the quantification of low-light-level emission signals from biological samples. Specificity is provided in the form of monoclonal antibodies and other ligands or enzyme substrates conjugated with efficient fluorophores. Fluorescent probes are also available for cellular macromolecular constituents and for free ions of biological interest such as H+ and Ca2+. The entire spectrum of photophysical phenomena can be exploited. Representative data are presented from studies of DNA conformation and architecture in polytene chromosomes and from studies of receptor-mediated endocytosis, calcium distribution, and the organization of the contractile apparatus in muscle cells.

Anthracycline resistance and consequences of the in situ-in vitro transfer

Adriamycin-resistant and normal cells of the sarcoma 180 of the mouse undergo qualitatively different deflections from the in situ state when prepared for an experiment. Resistant cells perform a fast reactive decline in the proliferative activity. They are capable of quiescence as defined by the time needed for the induction of the proliferation. Sensitive cells seem to be unable to quiesce and are only slowed down. These facts must be taken into account in interpretation of similar results. Differences in experiments need not necessarily imply differences in situ. Such in vitro appearing differences between sensitive and adriamycin-resistant cells of the murine sarcoma 180 include the retention of the mitochondria-specific stain rhodamine 123 and the uptake of anthracyclines, both being reduced in resistant cells. After labeling sensitive cells with thymidine in vivo and sorting them according to their rhodamine 123-derived fluorescence, the label was only found in the major, highly fluorescing fraction. A small low-fluorescing fraction remained unlabeled. We were able to demonstrate similar results with labeled anthracyclines applied to both the sensitive and the resistant cells in a short period between the removal of the cells from the ascites and the cell sorting. The adriamycin resistance seems to be joined with the ability of the cells to reduce their proliferative activity following changes to unfavorable conditions in vitro. Quiescent cells of the resistant line demonstrate the "anthracycline pump." Substances which are known to increase the sensitivity of anthracycline-resistant cells (TWEEN, verapamil) also shift the cells from low to high rhodamine 123-fluorescence.

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

Optical indicators of the cationic, cyanine and anionic oxonol classes were used to evaluate the plasma membrane potential of animal cells in suspension and in monolayer culture. The optical signals were calibrated by using diffusion potentials either of K+ (in the presence of valinomycin) or of H+ (in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone; FCCP); both classes of dye gave similar values of plasma membrane potential, in the range -40 to -90 mV for different cell types. Addition of haemolytic Sendai virus or Staphylococcus aureus alpha-toxin depolarizes cells and causes them to leak monovalent cations; these effects are antagonized by extracellular Ca2+. Cells infected with vesicular stomatitis or Semliki Forest virus become depolarized during an infectious cycle; infection with other viruses was without affect on plasma membrane potential.

Structural organization of interphase 3T3 fibroblasts studied by total internal reflection fluorescence microscopy

We studied the laminar organization of 3T3 fibroblast cells growing on glass slides by use of total internal reflection illumination to excite fluorescence emission (TIRF) from labeled molecules and stained cellular compartments that are very close to the cell-substrate contact region. Mitochondria, distant from the contact regions and stained with the water-soluble cationic dye, dil-C3-(3), fluoresced only as the glass/cytoplasm critical angle was approached. A similar result was obtained when the nuclei were stained with Hoechst dye 33342. From this measured angle a cytoplasmic refractive index in the range 1.358-1.374 was computed. The plasma membrane of 3T3 cells was stained with dil-C18-(3), and the cytoplasmic compartment was stained with fluoresceinyl-dextran (FTC-dextran) or with carboxyfluorescein. We have demonstrated a high degree of correspondence between the low-reflectance zones in the reflection interference image of a live cell and the TIRF images of both the plasma membrane and cytoplasmic compartment. TIRF photometry of selected contact regions of cells provided data from which the absolute separation of cell and substrate was computed. From a population of 3T3 cells microinjected with fluorescein-labeled actin, motile and adherent interphase cells were selected for study. For adherent cells, which displayed fluorescent stress fibers, the TIRF image was composed of intense patches and less intense regions that corresponded, respectively, to the focal contact and close-contact zones of the reflection-interference image. The intense patches corresponded to the endpoints of the stress fibers. Cells of motile morphology, which formed some focal contacts and extensive close-contact zones, gave AF-actin TIRF images of relatively even intensity. Thin lamellar regions of the cytoplasm were found to contain concentrations of actin not significantly different from other close-contact regions of the cell. The major analytical problem of TIRF microscopy is separation of the effects of proximity to substrate, refractive index, and fluorescent probe concentration on the local brightness of the TIRF image. From our results, it appears possible to use TIRF microscopy to measure the proximity of different components of substrate contact regions of cells.

Plasma membrane potential of Lettré cells does not depend on cation gradients but on pumps

The plasma membrane potential of Lettré cells has been determined with the optical indicator oxonol-V and found to be -57 mV at 37 degrees C (range -20 to -80 mV depending on the physiological condition of the cells). Increasing extracellular K+ does not depolarize cells: even in the presence of 155 mM K+ the potential is -41 mV; membrane potential is also insensitive to the chemical gradient of Na+, Mg2+, Ca2+ or Cl-. Ouabain depolarizes the cells; H+ efflux from cells is stimulated by extracellular Na+. We propose that in Lettré cells the plasma membrane potential is generated by electrogenic cation pumps. The balancing fluxes of Na+ and K+ are mainly through electroneutral cation exchanges (Na+/K+ and Na+/H+) and the magnitude of the potential is limited by organic anion leaks. Such a mechanism may operate in other biological membranes also.

The intracellular pH of quiescent and proliferating human and rat thymic lymphocytes

We compared the cytoplasmic pH (pHi) of quiescent and actively cycling thymic lymphocytes. Human and rat thymocyte suspensions were fractionated by centrifugation on one-step albumin density gradients. The pellet was composed of small, quiescent cells and the interphase contained mostly larger, actively cycling cells with a high proliferation index. When measured using [14C]-dimethyloxazolidinedione (DMO), pHi in the large cells of both species was approximately 0.15 units more alkaline than in the small cells. However, these differences were not detectable when pHi was measured with carboxylated fluorescein derivatives generated in situ by cytoplasmic enzymes. This apparent discrepancy can be explained by compartmentation of DMO, which accumulates in the alkaline mitochondrial matrix. Comparison of the mitochondrial content of quiescent and cycling thymocytes by several methods showed that the latter contained over 2.5-fold more mitochondria per unit cell volume. Assuming a constant intramitochondrial pH, this difference can account for the observed accumulation of DMO (i.e., apparent cytoplasmic alkalinity) in the actively proliferating cells. Therefore, no evidence was found for the existence of differences in pHi between quiescent and proliferating lymphocytes. Moreover, caution must be exercised when comparing DMO partition data in cells with varying relative mitochondrial content.

A novel method for measuring intracellular pH and potassium concentration

The concentration of Na+ and K+ and the pH in the cytoplasm of Lettré cells was measured by monitoring the net flux of H+, Na+, or K+ across the plasma membrane which had been rendered permeable to these ions by the action of Sendai virus. Ion flux was measured directly by analysis of cell composition, or indirectly by observing the change in membrane potential of cells treated with a specific ionophore. Cytoplasmic concentrations of cations were obtained by establishing the concentration of the cation in the medium at which addition of Sendai virus causes no change in cytoplasmic cation content. The value of Lettré-cell pH was confirmed by direct measurement employing 31P nuclear magnetic resonance, and the values of Na+ and K+ concentration were confirmed by analysis of cell cation and water content. Lettré cells suspended at 32 degrees C in Hepes-buffered saline at pH 7.3 maintain a cytosolic pH of 7.0 and contain 50 mM Na+ and 80 mM K+.

Multistation multiparameter flow cytometry: a critical review and rationale

The capacity for fluorescence excitation by beams of different wavelengths at separate points along the sample stream, and the capacity for computer analysis of multiparameter data thus obtained, are now available in flow cytometer/sorter systems from commercial producers. It is now readily apparent to most experienced users of flow cytometers that such multiparameter analysis offers the most convenient solution to the problem of characterizing subpopulations of cells within a mixed population. The use of multiple beams facilitates resolution of fluorescence signals from several probes within or upon a single cell and widens the range of analytical alternatives available to experimenters. This critical review discusses the history of the instrumentation, the parameters now measurable and the probes used for their measurement, and the methods for data analysis. Required sensitivity and precision are discussed, leading to the conclusion that many of the advantages of multistation, multiparameter flow cytometry can be made available in less complex and less costly instruments using less powerful sources and less elaborate computer hardware than are presently incorporated in commercial apparatus.

Unusual retention of rhodamine 123 by mitochondria in muscle and carcinoma cells

Mitochondria in cardiac muscle cells and myoblast-fused myotubes display unusually long (3-5 days) retention times of rhodamine 123, a mitochondria-specific fluorescent probe, in living cells. Among 50 keratin-positive carcinoma or transformed epithelial cell lines tested, mitochondria with prolonged rhodamine 123 retention are detected in most of the transitional cell carcinoma, adenocarcinoma, and chemical carcinogen-transformed epithelial cell lines and in some squamous cell carcinoma lines but not in any oat cell carcinoma lines. The presence of mitochondria having unusual dye retention may be useful for diagnosis and exploitable for chemotherapy of certain human carcinomas.

Exocytosis regulates urinary acidification in turtle bladder by rapid insertion of H+ pumps into the luminal membrane

Urinary acidification by the turtle bladder is due to a H+-ATPase that is located in the luminal membrane. The rate of H+ transport is stimulated by an increase in the ambient CO2. Using the fluorescent dye acridine orange, we showed that the mitochondria-rich cell of this equilibrium contains vesicles whose internal pH is acidic. We measured the pH of these vesicles by using endocytosed fluorescein isothiocyanate-labeled dextran and found it to be near 5.0. The pH increased after treatment with protonophores or metabolic inhibitors, suggesting that it was due to a H+ pump rather than to a Donnan effect. In bladders preloaded with fluorescent dextran, CO2 stimulated exocytosis and H+ transport measured simultaneously in the same bladder. The increase in the H+ current correlated well with the extent of exocytosis, and both were inhibited by pretreatment with colchicine. We conclude that the turtle bladder contains an intracellular reserve of vesicles containing H+ pumps and CO2 stimulates rapid fusion of these vesicles with the luminal membrane with consequent insertion of H+ pumps, thereby stimulating H+ secretion across the whole epithelium.