Phosphatidylserine translocation into brain mitochondria: involvement of a fusogenic protein associated with mitochondrial membranes

Data reported in the literature indicate that lipid movement between intracellular organelles can occur through contacts and close physical association of membranes (Vance, J.E. 1990. J Biol Chem 265: 7248-7256). The advantage of this mechanism is that the direct interaction of membranes provides the translocation event without the involvement of lipid-transport systems. However, pre-requisite for the functioning of this machinery is the presence of protein factors controlling membrane association and fusion. In the present work we have found that liposomes fuse to mitochondria at acidic pH and that the pre-treatment of mitochondria with pronase inhibits the fusogenic activity. Mixing of 14C-phosphatidylserine (PS) labeled liposomes with mitochondria at pH 6.0 results in the translocation of 14C-PS into mitochondria and in its decarboxylation to 14C-phosphatidylethanolamine through the PS decarboxylase activity localized on the outer surface of the inner mitochondrial membrane. Incorporation of 14C-PS is inhibited by the pre-treatment of mitochondria with pronase or with EEDQ, a reagent for the derivatization of the protonated form of carboxylic groups. These results indicate the presence of a protein associated with mitochondria which is able to trigger the fusion of liposomes to the mitochondrial membrane. A partial purification of a mitochondrial fusogenic glycoprotein is described in this work. The activity of the fusogenic protein appears to be dependent on the extent of protonation of the residual carboxylic groups and is influenced by the glucidic moiety, as demonstrated by its interaction with Concanavalin A. The purified protein is able to promote the recover of the 14C-PS import from liposomes to pronase-treated mitochondria. Therefore, the protein is candidate to be an essential component in the machinery for the mitochondrial import of PS.

A novel method for direct and fluorescence independent determination of drug efflux out of leukemic blast cells

Multi drug resistance (MDR) is often due to an increased efflux of anti cancer drugs out of leukemic blast cells. Efflux assays are used to get an impression of functional resistance in those cells. Dyes like rhodamine 123 or 3'3'-diethyloxocarbocyanine iodide are commonly used for this purpose. A major known disadvantage is that dyes do not behave like cytotoxic drugs in efflux experiments. Assays using the self fluorescence of drugs like anthracyclines can not reveal a real impression of intracellular or effluxed drug due to quenching of the drug fluorescence in the nuclei of the cells. We have developed a reproducible and sensitive assay for direct and quantitative determination of drug efflux out of blast cells. This was done by a novel double radioactive labelling using a 3H-labelled drug and 14C-labelled sucrose as extracellular marker. So this assay can be applied to every drug of interest. Quenching of fluorescence is also by-passed with this technique as well as protracting washing or silicon oil procedures. As a model system we used the T-lymphoblastoid cell line CCRF CEM and its resistant sublines vincristine 100 and adriamycin 5000. The results were also transferable to clinical specimens of leukemic patients. In conclusion our assay may be used for precise and direct efflux measurement of a broad range of anti-cancer drugs in clinical MDR evaluation.

Non-centrosomal microtubule formation and measurement of minus end microtubule dynamics in A498 cells

Experiments performed on a cell line (A498) derived from a human kidney carcinoma revealed non-centrosomal microtubules in the peripheral lamella of many cells. These short microtubules were observed in glutaraldehyde-fixed cells by indirect immunofluorescence, and in live cells injected with rhodamine-labeled tubulin. The non-centrosomal microtubules were observed to form de novo in living cells, and their complete disassembly was also observed. Low-light-level fluorescence microscopy, coupled to imaging software, was utilized to record and measure the dynamic behavior of both ends of the non-centrosomal microtubules in these cells. For each, the plus end was differentiated from the minus end using the ratio of their transition frequencies and by measuring total assembly at each end. For comparative purposes, dynamics of the plus ends of centrosomally nucleated microtubules were also analyzed in this cell line. Our data reveal several striking differences between the plus and minus ends. The average pause duration was nearly 4-fold higher at the minus ends; the percentage of time spent in pause was 92% at the minus ends, compared to 55% at plus ends. Dynamicity was decreased 4-fold at the minus ends, and the average number of events per minute was reduced from 7.0 at the plus end to 1.5 at the minus ends. The minus ends also showed a 6-fold decrease in frequency of catastrophe over the plus ends. These data demonstrate that in living cells, microtubules can form at sites distant from the perinuclear microtubule organizing center, and once formed, non-centrosomal microtubules can persist for relatively long periods.

Hepatic ischemia/reperfusion affects leukocyte rolling and velocity

Mechanisms of injury in hepatic ischemia/reperfusion injury are poorly defined. Leukocytes are thought to be important in the final mechanism of hepatic damage. We intend to show the time course of abnormal leukocyte activity in the liver after ischemia/reperfusion (I/R) injury. Left lobar hepatic ischemia was induced for 20 min in anesthetized C57B1-6 mice. Measurements were taken at control, reperfusion, and matching sham times (no ischemia) of 2, 5, 12, and 24 h. Measurements were taken using rhodamine and fluorescein enhanced intravital microscopy. Post sinusoidal venules were evaluated for numbers of rolling leukocytes, leukocyte saltation, and leukocyte velocity. Data are expressed as number of rolling leukocytes per 100 microns venule length (2 min). Statistical analysis was by ANOVA. The number of rolling leukocytes at 5, 12, and 24 h of reperfusion (p < 0.001) was significantly higher than control and sham-operated animals. Leukocyte velocities were significantly slower in the 12 h I/R group when compared to sham animals (p < 0.001). These data show that there are definable and quantifiable changes in leukocyte kinetics in the liver after ischemia/reperfusion. These changes, which lasted for 24 h, are likely due to upregulation of various endothelial cell adhesion molecules. Delineation of these mechanisms may be important in disease states such as shock, sepsis, and hepatic transplantation.

Cell cycle analysis and synchronization of pluripotent hematopoietic progenitor stem cells

Hematopoietic stem cells purified from mouse bone marrow are quiescent with less than 2% of Lin- Hoechst(low)/Rhodamine(low) (Lin- Ho(low)/Rho(low)) and 10% to 15% of Lin-/Sca+ cells in S phase. These cells enter proliferative cycle and progress through G1 and into S phase in the presence of cytokines and 5% heat-inactivated fetal calf serum (HI-FCS). Cytokine-stimulated Lin- Ho(low)/Rho(low) cells took 36 to 40 hours to complete first division and only 12 hours to complete each of 5 subsequent divisions. These cells require 16 to 18 hours to transit through G0/G1 period and 28 to 30 hours to enter into mid-S phase during the first cycle. Up to 56% of Lin- Rho(low)/Ho(low) cells are high-proliferative potential (7 factor-responsive) colony-forming cells (HPP-CFC). At isolation, HPP-CFC are quiescent, but after 28 to 30 hours of culture, greater than 60% are in S phase. Isoleucine-deprivation of Lin- Ho(low)/Rho(low) cells in S phase of first cycle reversibly blocked them from entering into second cycle. After the release from isoleucine-block, these cells exhibited a G1 period of less than 2 hours and entered into mid-S phase by 12 hours. Thus, the duration of G1 phase of the cells in second cycle is 4 to 5 times shorter than that observed in their first cycle. Similar cell cycle kinetics are observed with Lin-/Sca+ population of bone marrow cells. Stem cell factor (SCF) alone, in the presence of HI-FCS, is as effective as a cocktail of 2 to 7 cytokines in inducing quiescent Lin-/Sca+ cells to enter into proliferative cycle. Aphidicolin treatment reversibly blocked cytokine-stimulated Lin-/Sca+ cells at G1/S boundary, allowing their tight synchrony as they progress through first S phase and enter into second G1. For these cells also, SCF alone is sufficient for their progression through S phase. These studies indicate a very short G1 phase for stem cells induced to proliferate and offer experimental approaches to synchronize murine hematopoietic stem cells.

Sensitive analysis of [D-Pen2,5]enkephalin in rat serum by capillary electrophoresis and laser-induced fluorescence detection

A highly sensitive analytical method based on capillary zone electrophoresis (CZE) coupled with a laser-induced fluorescence (LIF) detector was explored for the analysis of [D-Pen2,5]enkephalin (DPDPE) in rat serum. DPDPE and the internal standard Phe-Leu-Glu-Glu-Ile (P9396) were extracted from serum samples with C18 solid-phase extraction disk cartridges, followed by derivatization with tetramethylrhodamine-5-isothiocyanate (TRITC) isomer G before introduction onto the capillary column. Complete resolution of DPDPE and the internal standard from other serum components was achieved within 20 min on a 140 cm x 50 microns I.D. capillary column with borate buffer (25 mM. pH 8.3). With the current method, it is possible to detect 1.3E-18 mol of DPDPE on column. The results suggest that CZE-LIF is a promising method for the sensitive and specific quantitation of therapeutic peptides in biological matrices.

Probes bound to myosin Cys-707 rotate during length transients in contraction

It is widely conjectured that muscle shortens because portions of myosin molecules (the "cross-bridges") impel the actin filament to which they transiently attach and that the impulses result from rotation of the cross-bridges. Crystallography indicates that a cross-bridge is articulated-consisting of a globular catalytic/actin-binding domain and a long lever arm that may rotate. Conveniently, a rhodamine probe with detectable attitude can be attached between the globular domain and the lever arm, enabling the observer to tell whether the anchoring region rotates. Well-established signature effects observed in shortening are tension changes resulting from the sudden release or quick stretch of active muscle fibers. In this investigation we found that closely correlated with such tension changes are changes in the attitude of the rhodamine probes. This correlation strongly supports the conjecture about how shortening is achieved.

Direct measurement of endosomal pH in living cells of the rat yolk sac epithelium by laser confocal microscopy

Endocytosis of dual-fluorescent dextran by epithelial cells was observed in the perfused rat yolk sac using a confocal laser scanning microscope. Endosomal pH was quantified from confocal images using a dual-fluorescence ratiometry technique. Changes in endosomal pH were followed over time up to 32 min with and without Brefeldin A treatment. After 4 min of endocytosis without Brefeldin A, endosomes had a pH of 6.1 +/- 0.3. After 16 min and 32 min, their pH levels varied widely from 4.0 to 6.6. When Brefeldin A (10 microM) was added to the perfusion medium, endosomal pH remained fairly stable in the range of 6.0 to 6.2 from 4 min to 32 min. The corresponding endosomal structures were examined by electron microscopy after endocytic labeling with horseradish peroxidase. After 4 min, small endocytic vesicles and large endosomal vacuoles with tubular extensions were labeled. After 16 min and 32 min, multivesicular bodies and dense lysosomal structures were progressively labeled, but their labeling was almost undetectable after Brefeldin A treatment. These results suggested that the pH within the sorting compartment of early endosomes is 6.1 +/- 0.3. This is the first quantitative measurement of pH within sorting endosomes in intact cells of the living yolk sac epithelium.

Connections of the caudal ventrolateral medullary reticular formation in the cat brainstem

A region of the caudal ventrolateral medullary reticular formation (CVLM) participates in baroreceptor, vestibulosympathetic, and somatosympathetic reflexes; the adjacent retroambigual area is involved in generating respiratory-related activity and is essential for control of the upper airway during vocalization. However, little is known about the connections of the CVLM in the cat. In order to determine the locations of terminations of CVLM neurons, the anterograde tracers Phaseolus vulgaris leucoagglutinin and tetramethylrhodamine dextran amine were injected into this region. These injections produced a dense concentration of labeled axons throughout the lateral medullary reticular formation (lateral tegmental field), including the retrofacial nucleus and nucleus ambiguus, regions of the rostral ventrolateral medulla, the lateral and ventrolateral aspects of the hypoglossal nucleus, nucleus intercalatus, and the facial nucleus. A smaller number of labeled axons were located in the medial, lateral, and commissural subnuclei of nucleus tractus solitarius, the A5 region of the pontine reticular formation, the ventral and medial portions of the spinal and motor trigeminal nuclei, locus coeruleus, and the parabrachial nucleus. We confirmed the projection from the CVLM to both the rostral ventrolateral medulla and lateral tegmental field using retrograde tracing. Injections of biotinylated dextran amine or Fluorogold into these regions resulted in retrogradely labeled cell bodies in the CVLM. However, the neurons projecting to the lateral tegmental field were located mainly dorsal to those projecting to the rostral ventrolateral medulla, suggesting that these neurons form two groups, possibly with different inputs. Injections of retrograde tracers into the lateral tegmental field and rostral ventrolateral medulla also produced labeled cell bodies in other regions, including the medial and inferior vestibular nuclei and nucleus solitarius. These data are consistent with the view that the CVLM of the cat is a multifunctional area that regulates blood pressure, produces vocalization, affects the shape of the oral cavity, and elicits contraction of particular facial muscles.

Assessment of the effects of gramicidin, formaldehyde, and surfactants on Escherichia coli by flow cytometry using nucleic acid and membrane potential dyes

Two membrane potential sensitive dyes (Rhodamine 123 and bis-oxonol) and three nucleic acid dyes (propidium iodide, SYTO-13, and SYTO-17) were used to assess the effect of surfactants on Escherichia coli. The ability of E. coli to be stained by these probes was validated at different physiological states. Propidium iodide was used to assess the integrity of cell envelopes. Two double staining methods based on propidium iodide with SYTO-13 and bis-oxonol with SYTO-17 were used to improve the discrimination between bacteria and micelles or aggregated particles generated by the presence of surfactants. A rapid (1 h contact time between cells and surfactants, and less than 5 min for staining and obtaining data) Rhodamine 123 flow cytometric assay was developed to assess the bactericidal effect of surfactants.

[Flow cytometric analysis of P-glycoprotein function by rhodamine 123 dye-efflux assay in human leukemia cells]

Cells with multidrug resistance(MDR) phenotype express P-glycoprotein(P-gp) on cell membrane, which works as a drug-efflux pump with low selectivity. P-gp function can be determined microfluorometrically using the fluorescent dye rhodamine 123(Rh123), which is an artificial substrate for P-gp. In this study, we assessed P-gp function in human leukemia sublines of MOLT-3 with various magnitude of MDR phenotype using the Rh123-efflux assay. The MDR cells efficiently pumped out Rh123 outside cells in parallel with the magnitude of resistance to vincristine, while the parent MOLT-3 cells scarcely showed dye efflux. The P-gp function determined by the dye efflux assay was correlated with the degree of cell surface expression of P-gp measured by indirect flow cytometric analysis using MRK16 anti-P-gp antibody and with the amount of MDR1 mRNA (encoding P-gp) quantified by Northern blot analysis and by competitive reverse transcription-polymerase chain reaction (RT-PCR) assay. In the evaluation of 28 clinical samples obtained from patients with leukemias, 9 cases exhibited positive results Rh123-efflux. A good correlation of Rh123-efflux with MDR1 expression measured by competitive RT-PCR was observed in these samples. Since subpopulations of normal lymphocytes show low degree of P-gp function, the strict gating of leukemia cells was mandatory in the dye-efflux assay in clinical samples. Although leukemia cells could not be distinguished from normal lymphocytes in the conventional scattergram in some cases, additional staining of the former cells with specific monoclonal antibody such as CD34(labelled with PE-Cy5, a dye without interference with Rh123 fluorescence emission) enabled a selective analysis of a particular subpopulation. The Rh123 dye-efflux assay is a simple and sensitive method for the determination of P-gp expression and its function, and is particularly suitable for the analyses in the clinical laboratory.

Quantification of P-glycoprotein in chronic lymphocytic leukemia by flow cytometry

The P-glycoprotein (P-gp) was investigated in 40 patients with chronic lymphocytic leukemia by immunological, functional and quantitative assays. The proportion of positive cases with the anti-Pgp McAb UIC2 was 30% and increased to 64% after neuraminidase treatment (p = 0.002). Fifty-six per cent of cases were positive with the functional test with rhodamine 123 and verapamil. A negative correlation was found between the number of cells stained with the McAb and the functional test (p = 0.006). The mean of P-gp molecules was 2509 +/- 2805 molecules per cell; these values were higher than in the control K562 cell line in the majority of cases. The number of positive cases and P-gp molecules were higher in treated than in untreated patients (p = 0.01 and 0.07). There were no significant differences with respect to response to treatment, but a higher number of P-gp molecules was found in non-responders. When the results of the functional test were put together with the quantification assay this allowed the detection of 71% non-responders. Our findings suggest that quantification of the P-gp could be of value in the assessment of possible drug resistance in CLL.

Radioactive technetium-99m labelling of Salmonella abortusovis for the assessment of bacterial dissemination in sheep by in vivo imaging

We report the development and validation of a 99mTc-labelling technique of bacteria, applied to Salmonella abortusovis. The radioactive labelling is obtained using a pre-tinning step of the cells followed by direct incubation of S. abortusovis suspension with 99mTc-pertechnetate. Several procedures with different amounts of stannous tin (SnF2 or SnCl2) were evaluated. The selected method, respectful of bacterial viability, provided a 30% labelling yield. Viability of 99mTc-labelled bacteria was assessed by flow cytometry using rhodamine 123 and was demonstrated to be unchanged, turbidimetric measurements showing only a slight increase in the growth rate for radiolabelled cells. Incubation of 99mTc-labelled S. abortusovis with pronase, saponine and urea demonstrated labelling stability and suggested an intra-cellular localization for 99mTc. A preliminary study was also conducted in sheep to evaluate the value of the imaging of radiolabelled S. abortusovis. Spatial and temporal patterns of their in vivo dissemination in the lymphatic system after a sub-cutaneous injection were compared with control lymphoscintigraphic agents. These imaging data supported the assumption that the radioactivity detected in vivo was proportional to the number of 99mTc-labelled bacteria.

2',3'-Dideoxycytidine cytotoxicity in human macrophages

Human macrophages when cultured for several weeks in the presence of therapeutically relevant 2',3'-dideoxycytidine (ddC) concentrations show a time-dependent decay in mitochondrial DNA content. This decay is associated with a reduction of Rhodamine 123 fluorescence, a marker for mitochondrial membrane potential suggesting that impairment of mitochondrial functions occurs. Mitochondrial metabolic impairment was confirmed by direct evaluation of lactate production, which is markedly increased in cells treated with ddC. The activity of protein kinase C and intracellular free Ca2+ upon addition of phorbol 12-myristate 13-acetate (PMA) were lower in the drug-treated cells compared to controls. A 50% reduction in O2-release was also found upon PMA stimulation. Fluorescent latex beads, yeast and bacteria phagocytosis were normal, but intracellular bacteria killing was markedly impaired in ddC-exposed macrophages. Thus, ddC exerts a delayed mitochondrial toxicity also on differentiated macrophages with impairment of several metabolic properties and O2 production causing a reduced ability of these phagocytic cells to kill phagocytosed bacteria.

Preferential uptake of small-aggregate fraction of pulmonary surfactant in vitro

Homeostasis of pulmonary surfactant requires metabolic clearance of surfactant forms with decreased surface activity. Rabbit pulmonary surfactant was labeled in vivo with rhodamine-labeled dipalmitoylphosphatidylethanolamine (R-DPPE), isolated, and fractionated into large- and small-aggregate subfractions by differential centrifugation. Endocytosis of large (LA)- and small (SA)-aggregate surfactant by a mouse lung epithelial cell line (MLE-12) was evaluated in vitro by epifluorescence microscopy. More SA than LA surfactant was taken up by MLE-12 cells. Endocytosis of SA and LA surfactant was inhibited by preincubation of the subfractions with surfactant protein A and 3.3 mM Ca2+. The difference in uptake between SA and LA surfactant was lost for reconstituted organic extracts of the subfractions. Much of the difference in uptake of SA and LA surfactant may be attributed to the greater concentration of surfactant protein A in LA surfactant.

A nuclear localization signal targets proteins to the retrograde transport system, thereby evading uptake into organelles in aplysia axons

The turnover of soluble proteins in axons and terminals is effected by replacing used proteins with newly synthesized constituents from the cell body. To investigate this complex process, which is especially important during nerve regeneration, we microinjected proteins into varicosities on axons of Aplysia neurons in vitro. When human serum albumin (HSA) coupled to rhodamine (r) was injected, it initially filled the varicosity; within seconds, however, it began to accumulate in packets and by 15 min was punctate. A similar pattern was observed after injecting soluble proteins from extruded axoplasm. In contrast, when we injected rHSA covalently attached to the SV-40 nuclear localization sequence (sp), the distribution was never punctate and the rHSA-sp was retrogradely transported from the varicosity to the cell body and into the nucleus. Electron microscopy of varicosities injected with HSA-gold showed that >90% of the particles were inside vacuoles and multivesicular bodies. These organelles probably function as storage rather than degradatory sites since they did not contain acid phosphatase. In contrast, when HSAsp-colloidal gold was injected, only 25% of the particles were in organelles. Thus, HSA and resident axonal proteins can be removed from axoplasm by uptake into organelles. The presence of a nuclear localization sequence (the sp) may avoid uptake by providing access to the retrograde transport/nuclear import pathway.

Fluorescent measurement of the intracellular pH during sporulation of Saccharomyces cerevisiae

This work reports the intracellular pH (pHi) dynamics of Saccharomyces cerevisiae cells in sporulation medium. Cells loaded with the pH-sensitive dye carboxy-seminaphthorhodafluor-1 (C.SNARF-1) exhibited an alkalization of the pHi following the extracellular pH during sporulation in the absence of buffer and almost no change in pHi or delta pH when sporulation was carried out in buffered medium. The results indicate that the pH gradient does not appear to be directly involved in the regulation of acetate uptake during sporulation. However, the alkalization of pHi by eliciting a decrease in metabolic fluxes could account for a lower demand for acetate.

Down-regulation of topoisomerase II by camptothecin does not prevent additive activity of the topoisomerase II inhibitor etoposide in vitro

Topoisomerases (Topo) I and II are cellular enzymes that catalyze the relaxation of topologically strained DNA and that are involved in a number of DNA-related processes. Their complete inhibition by Topo I and II inhibitors gives promise for improvements in the treatment of malignant diseases. However, preclinical studies showed down-regulation of Topo II protein expression by Topo I inhibitors, which may preclude the useful application of combined topoisomerase inhibition in the clinic. We investigated the efficacy of the combination of etoposide (ETP) and camptothecin (CPT) in human gastric and lung cancer cell lines with different sensitivity towards ETP. The cytotoxicity of different drugs was assessed by the sulforhodamine B assay. Drug interactions were evaluated by isobologram analysis. The polymerase chain reaction and flow cytometry were employed for examination of the mdr1 (multidrug resistance type 1) phenotype. As reported by others, incubation of the P glycoprotein (P-gp)-negative tumor cell lines with the Topo I inhibitor CPT resulted in a significant down-regulation of Topo II protein expression. This was obviously due to changes in the cell cycle distribution of the cells induced by the treatment, with a marked increase of cells in G2/M phase and a consecutive decrease of S phase cells. Despite these biochemical changes, isobologram analysis showed additive cytotoxic activity of CPT and ETP in all the cell lines, independent of whether the drug incubation was performed simultaneously or sequentially. These data indicate that down-regulation of Topo II protein by CPT does not prevent additive activity of CPT and ETP in vitro, and therefore combined Topo I and II inhibition may be useful for investigation in clinical trials.

Aggregation reroutes molecules from a recycling to a vesicle-mediated secretion pathway during reticulocyte maturation

Endocytosis of the Tf/TfR complex is essentially the only pathway active in maturing reticulocytes, while exosomes, formed by invagination of the endosomal membrane, provide a mechanism to eliminate seemingly obsolescent proteins, including the TfR, when their function is completed. In this study, we examined molecular trafficking in the recycling and exosome-directed pathways during endocytosis in maturing reticulocytes. To this end, the flow of two exogenously inserted fluorescent lipid analogs, N-(N-[6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl]) sphingomyelin (C6-NBD-SM) and N-(lissamine rhodamine B sulfonyl) phosphatidyl ethanolamine (N-Rh-PE) was monitored and compared to that of the transferrin (Tf)/Tf receptor (TfR) complex. Prior to elimination via exosomes, the TfR actively recycles with a half-time of approx. 2 minutes. The recycling kinetics of C6-NBD-SM, as bulk plasma membrane marker, are identical to those of the apoTf/TfR complex, as shown by fluorescence microscopy and biochemical analysis. By contrast, although efficiently internalized along the same pathway, N-Rh-PE does not return to the cell surface. More specifically, sucrose gradient analysis and immunoisolation experiments demonstrated that N-Rh-PE accumulates in exosomes, which are eventually released into the extracellular medium. Fluorometric measurements showed that exogenously inserted N-Rh-PE is present in the reticulocyte plasma membrane as small molecular clusters. Moreover, a close correlation was observed between the fate of crosslinked proteins, including the TfR and acetylcholinesterase (AChE), and the fate of the clustered lipid N-Rh-PE. Thus antibody-induced aggregation of specific proteins like the TfR and AChE, which are normally sorted into exosomes during reticulocyte maturation, enhances their shedding by the exosomal pathway. Taken together, the results support the hypothesis that aggregation of either proteins or lipids act as a general sorting signal for exosomal processing, thereby inhibiting reentry in a recycling pathway and providing an effective means for clearing molecules from the cell surface and their eventual elimination from the cells.

Whole-cell hybridization of Methanosarcina cells with two new oligonucleotide probes

Two new oligonucleotide probes targeting the 16S rRNA of the methanogenic genus Methanosarcina were developed. The probes have the following sequences (Escherichia coli numbering): probe SARCI551, 5'-GAC CCAATAATCACGATCAC-3', and probe SARCI645, 5'-TCCCGGTTCCAAGTCTGGC-3'. In situ hybridization with the fluorescently labelled probes required several modifications of standard procedures. Cells of Methanosarcina mazeii S-6 were found to lyse during the hybridization step if fixed in 3% formaldehyde and stored in 50% ethanol. Lysis was, however, not observed with cells fixed and stored in 1.6% formaldehyde-0.85% NaCl. Extensive autofluorescence of the cells was found upon hybridization in the presence of 5 mM EDTA, but successful hybridization could be obtained without addition of this compound. The mounting agent Citifluor AF1, often used in conjugation with the fluorochrome fluorescein, was found to wash the labelled probes out of the cells. Stable labelling could be obtained with rhodamine-labelled probes when the specimen was mounted in immersion oil, and high hybridization intensities of the Methanosarcina cells were found even in the presence of biomass from an anaerobic reactor. The inherent high autofluorescence of the biomass could be lowered by use of a highly specific narrow-band filter. The probes were found to be specific for Methanosarcina and useful for detection of this genus in samples from anaerobic reactors.

Energetic requirement of insulin secretion distal to calcium influx

A number of agents that inhibit oxidative phosphorylation by different mechanisms (carbonyl cyanide mchlorophenylhydrazone [CCCP], sodium azide, oligomycin) induced an increase of cytoplasmic Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells, as measured by microfluorimetry with digital imaging. All three agents are known inhibitors of insulin secretion, and the secretory response to 20 mmol/l glucose was found to be abolished in spite of elevated [Ca2+]i. Two reasons could account for this dissociation between increase of [Ca2+]i and insulin secretion: 1) the increase did not take place at a site critical for exocytosis, 2) a threshold concentration of a metabolism-derived factor like ATP exists for the induction of exocytosis. The increase of [Ca2+]i by CCCP and sodium azide involved release of Ca2+ from internal stores, whereas oligomycin induced a slow D 600-inhibitable Ca2+ influx. Because CCCP and sodium azide, but not oligomycin, decreased the mitochondrial membrane potential concomitantly with the increase of [Ca2+]i, release of Ca2+ from the mitochondria most probably plays a decisive role for the internal mobilization. A Ca2+ influx induced by 40 mmol/l K+ or 250 micromol/l tolbutamide was unimpaired in the presence of oligomycin, but oligomycin completely abolished insulin secretion in response to these agents. While CCCP and sodium azide opened ATP-sensitive K+ channels, oligomycin was virtually ineffective, although it could be shown to significantly reduce beta-cell ATP production. By comparison of the effects of different inhibitors of oxidative phosphorylation, we conclude that the initiation of exocytosis in beta-cells is particularly sensitive to a decrease of energy metabolism, more than ATP-sensitive K+ channels or voltage-dependent Ca2+ channels. Thus, any increase of [Ca2+]i in beta-cells that occurs in a situation of a decreased ATP supply is unlikely to elicit a secretory response.

Photoactivation of caged compounds in single living cells: an application to the study of cell locomotion

Caged compounds are molecules whose biological function is masked until UV light induces a photo-chemical reaction that converts the molecules into a biologically active state. These probes provide very powerful tools in cell biology research, since the activation can be precisely controlled temporally and spatially by limiting their exposure to light. This report describes a simple caged compound illuminator that can be attached to an inverted microscope; it can simultaneously provide both sufficient UV illumination for photoactivation and epifluorescence excitation to monitor indicator fluorescence. As an example, we show that the cytoplasmic calcium level can be raised very rapidly by the photoactivation of a new caged compound, caged calcium ionophore DMNPE-A23187, and that this [Ca2+]i increase is associated with tail retraction of motile keratocytes.

Dentin bonding: effect of tubule orientation on hybrid-layer formation

In an attempt to compare the morphology of the resin-dentin interface in areas where the dentinal tubules run perpendicularly or at an angle to the cavity surface with that of areas where they run parallel to it, we studied a dentin adhesive system using transmission electron microscopy and fluorescence confocal laser scanning microscopy. The design of the study included the simulation of the normal hydrostatic pressure within the pulp and the dentinal tubules. Following acid etching of the dentinal surface with maleic acid/HEMA, the smear layer was removed, and a superficial zone was demineralized in such a way that the exposed collagenous dentin matrix retained its integrity. Confocal laser scanning microscopal investigations using primer labeled with rhodamine B showed that the penetration of the primer occurred not only vertically via surface porosities, but mainly laterally, via the dentinal tubules. The adhesive resin labeled with fluorescein completely infiltrated the demineralized layer, thereby forming a hybrid layer. The orientation of the dentinal tubules had a profound effect on the formation of the hybrid layer. In areas with perpendicular tubule orientation, the layer was 3.2 +/- 0.8 microns thick, showing solid 27.2 +/- 0.8 microns long resin tags in the dentinal tubules, and a network of tiny tags in their side-branches. In areas with parallel tubule orientation the layer was significantly thinner (1.3 +/- 0.6 microns) and resin tags were absent.

Parallel input to the hippocampal memory system through peri- and postrhinal cortices

In the rat, the rhinal cortices consist of the perirhinal, postrhinal and entorhinal cortices. The perirhinal and postrhinal cortices, which serve as major input sources to the entorhinal cortex, receive functionally different types of information. In this study we looked at the projections from the perirhinal and postrhinal cortices to the different parts of the entorhinal cortices using an anterograde tracing technique. Our results show that the perirhinal cortex preferentially projects to the lateral entorhinal cortex, whereas the postrhinal cortex mainly sends fibers to the medial entorhinal cortex. Since the lateral and medial entorhinal cortices are differentially connected with the hippocampus, we suggest that functionally different types of information are processed in parallel in the hippocampal memory system.

Association of serotonin-like immunoreactive axons with nociceptive projection neurons in the caudal spinal trigeminal nucleus of the rat

Serotoninergic projections to the spinal dorsal horn are implicated in the modulation of nociceptive transmission. However, morphological evidence indicating that serotoninergic projection fibers make synapses on nociceptive neurons in the medullary dorsal horn is still meager. Thus, we examined whether axonal varicosities with serotonin (5-HT)-like immunoreactivity (5-HT-LI) might make synapses on nociceptive projection neurons in the caudal spinal trigeminal nucleus (Vc) of the rat. Projection neurons were retrogradely labeled with tetramethylrhodamine-dextran amine (TMR-DA) or wheat germ agglutinin-horseradish peroxidase (WGA-HRP) that was injected into the parabrachial or thalamic region. Vc neurons in which c-fos protein-like immunoreactivity (Fos-LI) was induced by subcutaneous injection of formalin into the lip were considered nociceptive. Vc neurons in direct contact with axonal varicosities that bind isolectin I-B4 were also considered nociceptive. Triple labeling for 5-HT, TMR-DA, and Fos as well as that for 5-HT, TMR-DA, and I-B4 were done by using the immunofluorescence and fluorescence histochemical techniques. Confocal laser-scanning microscopy revealed that axonal varicosities with 5-HT-LI were in close apposition to TMR-DA-labeled neurons showing Fos-LI in lamina I and the outer part of lamina II (lamina IIo), and that both axonal varicosities with 5-HT-LI and those binding I-B4 were in close apposition to single neuronal profiles labeled with TMR-DA. The presumed nociceptive neuronal profiles in close apposition to axon terminals with 5-HT-LI were mainly those of laminae I and II neurons as well as dendrites of lamina III neurons. Electron microscopy confirmed that axon terminals with 5-HT-LI and those with I-B4 binding activity in laminae I and II made synapses on somatic and dendritic profiles that were labeled with WGA-HRP. The results indicate that serotoninergic neurons project directly on nociceptive projection neurons in the Vc.