Development of a fluorescent indicator for the bioimaging of nitric oxide

High-throughput probing macrophage-bacteria interactions at the single cell level with microdroplets

Pathogenic infections may lead to disruption of homeostasis, thus becoming a serious threat to the human health. Understanding the interactions between bacteria and macrophages is critical for therapeutic development against sepsis or inflammatory bowel disease. Here, we report a technique using droplet biosensors for the detection of nitric oxide (NO) secreted by a single macrophage under inflammatory stimuli. We demonstrated that the limit of detection can be promoted more than two orders of magnitude by our approach, in comparison to the conventional microplate format. The experiments of co-encapsulating single macrophages and different numbers of Escherichia coli (E. coli) enabled fluorescence monitoring of NO secretion by single macrophages over the incubation, and investigation of their interactions inside the isolated droplet for their separate fates. Our approach provides a unique platform to study the bacteria-macrophage interactions at the single cell level.

Human Induced Pluripotent Stem Cell-Derived Vascular Cells: Recent Progress and Future Directions

Human induced pluripotent stem cells (hiPSCs) hold great promise for cardiovascular regeneration following ischemic injury. Considerable effort has been made toward the development and optimization of methods to differentiate hiPSCs into vascular cells, such as endothelial and smooth muscle cells (ECs and SMCs). In particular, hiPSC-derived ECs have shown robust potential for promoting neovascularization in animal models of cardiovascular diseases, potentially achieving significant and sustained therapeutic benefits. However, the use of hiPSC-derived SMCs that possess high therapeutic relevance is a relatively new area of investigation, still in the earlier investigational stages. In this review, we first discuss different methodologies to derive vascular cells from hiPSCs with a particular emphasis on the role of key developmental signals. Furthermore, we propose a standardized framework for assessing and defining the EC and SMC identity that might be suitable for inducing tissue repair and regeneration. We then highlight the regenerative effects of hiPSC-derived vascular cells on animal models of myocardial infarction and hindlimb ischemia. Finally, we address several obstacles that need to be overcome to fully implement the use of hiPSC-derived vascular cells for clinical application.

Sensing Nitric Oxide in Cells: Historical Technologies and Future Outlook

Nitric oxide (NO) is a critical cell signaling molecule with important roles in both normal cellular physiology and pathology. Over the past 20 years, multiple sensing modalities have been developed for the intracellular synthesis (endogenous) and release (exogenous) of NO. In this review, we survey the historical progression of NO sensing platforms, highlight the current state of the art, and offer a forward-looking view of how we expect the field of NO sensing to develop in the context of recent advances in bio-nanotechnology and nanoscale cellular biosensors.

Recent progress on the organic and metal complex-based fluorescent probes for monitoring nitric oxide in living biological systems

Nitric oxide (NO) is an important gaseous signaling molecule related to various human diseases. To investigate the biological functions of NO, many strategies have been developed for real-time monitoring the NO levels in biological systems. Among these strategies, fluorescent probes are considered to be one of the most efficient and applicable methods owing to their excellent sensitivity and selectivity, high spatiotemporal resolution, noninvasiveness, and experimental convenience. Therefore, great efforts have been paid to the design, synthesis, and fluorescence investigation of novel NO fluorescent probes in the past several years. However, few of them exhibit practical applications owing to the low concentration, short half-life, and rapid diffusion characteristics of NO in biological systems. Rational design of NO fluorescent probes with excellent selectivity and sensitivity, low cytotoxicity, long-lived fluorescent emission, and low background interference is still a challenge for scientists all over the word. To provide spatial-temporal information, this article focuses on the progress made in the organic and metal complex-based NO fluorescent probes during the past five years. The key structural elements and sensing mechanisms of NO fluorescent probes are discussed. Some novel ratiometric, luminescence, and photoacoustic probes with low background interference and deep tissue penetrating ability are mentioned. All these probes have been used for imaging exogenous and endogenous NO in cells and animal models. More importantly, this article also describes the development of multi-functional NO fluorescent probes, such as organelle targeting probes, dual-analysis probes, and probe-drug conjugates, which will inspire the design of various functional fluorescent probes.

A rhodamine-based fast and selective fluorescent probe for monitoring exogenous and endogenous nitric oxide in live cells

A sensitive and selective fluorescent probe for fast detection of nitric oxide was synthesized by grafting a NO-trapper o-phenylenediamine onto a rhodamine fluorophore.

An Amphiphilic Fluorescent Probe Designed for Extracellular Visualization of Nitric Oxide Released from Living Cells

Nitric oxide (NO) is an intracellular and intercellular messenger involved in numerous physiological and pathophysiological processes. Small-molecule fluorescent probes coupled with fluorescence microscopy provide excellent tools for real-time detection of NO in situ. However, most probes are designed for imaging intracellular NO, which cannot reflect the release behavior of endogenously produced NO. In order to visualize extracellular NO released from living cells, we report herein a particularly designed amphiphilic fluorescent probe, disodium 2,6-disulfonate-1,3-dimethyl-5-hexadecyl-8-(3,4-diaminophenyl)-4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (DSDMHDAB), in which hydrophilic groups are introduced to keep the fluorophore and recognition domain outside the cell and a hydrophobic C16 alkyl chain acts as the membrane anchor. Based on this design, NO released out of the cells has been visualized on the outer surface of the plasma membrane. Using RAW 264.7 cells and ECV-304 cells as models, the diffusion of NO across the plasma membrane has been directly observed. The amphiphilic design strategy of fluorescent probes holds great promise for developing fluorescent imaging probes to study the release behaviors of other endogenous gasotransmitters.

Fluorescence turn-on for the highly selective detection of nitric oxide in vitro and in living cells

A water-soluble, biocompatible, small molecular fluorescent turn-on probe was developed for the highly selective and sensitive detection of NO in vitro and in living cells.

The apoptosis of peripheral blood lymphocytes promoted by hyperbaric oxygen treatment contributes to attenuate the severity of early stage acute pancreatitis in rats

The aim of this study was to investigate the immunoregulatory effects of hyperbaric oxygen (HBO) via promoting the apoptosis of peripheral blood lymphocytes (PBLs) to attenuate the severity of early stage acute pancreatitis (AP) in rats. Additionally, the persistence of the HBO treatment effects was evaluated. One hundred and twenty male Wistar rats were randomized into four groups: sham, AP, AP + normobaric oxygen (NBO), and AP + HBO. Each group consisted of 30 rats. Four hours after the induction of AP, the 30 rats in the AP + NBO group were given normobaric oxygen treatment with 100 % oxygen at 1 atm for 90 min. The 30 rats in the AP + HBO group received 100 % oxygen at 2.5 atm for 90 min, with a compression/decompression time of 15 min. The 30 rats in the AP group remained untreated. At 6, 12, and 24 h after the induction of AP, surviving rats from each group were sacrificed, and the blood and tissue samples were collected for the following measurements: the partial pressure of oxygen (PaO2) and oxygen saturation (SaO2) of the arterial blood, the levels of serum amylase, lipase, interleukin-2 (IL-2), interferon-γ (IFN-γ), interleukin-10 (IL-10), hepatocyte growth factor (HGF), and reactive oxygen species (ROS), and the mitochondrial membrane potential (∆Ψm) of the PBLs. The expression levels of procaspase-3, caspase-3, procaspase-9, and caspase-9 were also evaluated in the PBLs. Additionally, the apoptosis of PBLs was assessed, and the pancreatic tissues were subjected to a histopathological analysis by pathological grading and scoring. The histopathology of the lung, liver, kidney, duodenum, and heart was also analyzed at 12 h after the induction of AP. Significant differences were found at 6 and 12 h after AP induction. The HBO treatment significantly elevated the PaO2 and SaO2 levels, and the ROS levels in the PBLs. Additionally, HBO downregulated the levels of amylase and lipase. The HBO treatment also reduced the ∆Ψm levels, upregulated the expression of caspase-3 and caspase-9, and increased the apoptosis rate of the PBLs. Moreover, the HBO treatment decreased the serum concentrations of IL-2, IFN-γ and HGF, and reduced the pathological scores of the pancreatic tissue. The histopathological changes of the lung, liver, kidney, duodenum, and heart were also improved. A significant elevation of IL-10 occurred only at the 12-h time point. However, no obvious differences were found at the 24-h time point. This study demonstrated that the HBO treatment can promote the apoptosis of PBLs via a mitochondrial-dependent pathway and inhibit the inflammatory response. These immunoregulatory effects may play an important therapeutic role in attenuating the severity of early stage AP. The repeated administration of HBO or the use of HBO in combination with other approaches may further improve outcomes.

A mitochondria-targetable fluorescent probe for dual-channel NO imaging assisted by intracellular cysteine and glutathione

A mitochondria-specific fluorescent probe for NO (1) was synthesized by the direct conjugation of a pyronin dye with one of the amino groups of o-phenylenediamino (OPD). The probe could selectively detect NO over dehydroascorbic acid (DHA), ascorbic acid (AA), and methylglyoxal (MGO) as well as the reactive oxygen/nitrogen species (ROS/RNS) with the significant off-on response due to the production of a red-emission triazole 2. In the presence of cysteine/glutathione (Cys/GSH), 2 could be further transformed into a green-emission aminopyronin 4 and a red-emission thiopyronin 5, respectively. Assisted by intracellular Cys and GSH, the probe demonstrated its potential to monitor mitochondrial NO in a dual-channel mode.

A specific fluorescent probe for NO based on a new NO-binding group

A highly selective fluorescent probe for NO was exploited based on a specific NO-binding group, 2-amino-3′-dimethylaminobiphenyl.

Characterization of a fluorescent probe for imaging nitric oxide

BACKGROUND

Nitric oxide (NO), a potent vasodilator and anti-atherogenic molecule, is synthesized in various cell types, including vascular endothelial cells (ECs). The biological importance of NO enforces the need to develop and characterize specific and sensitive probes. To date, several fluorophores, chromophores and colorimetric techniques have been developed to detect NO or its metabolites (NO(2) and NO(3)) in biological fluids, viable cells or cell lysates.

METHODS

Recently, a novel probe (NO(550)) has been developed and reported to detect NO in solutions and in primary astrocytes and neuronal cells with a fluorescence signal arising from a nonfluorescent background.

RESULTS

Here, we report further characterization of this probe by optimizing conditions for the detection and imaging of NO products in primary vascular ECs, fibroblasts, and embryonic stem cell- and induced pluripotent stem cell-derived ECs in the absence and presence of pharmacological agents that modulate NO levels. In addition, we studied the stability of this probe in cells over time and evaluated its compartmentalization in reference to organelle-labeling dyes. Finally, we synthesized an inherently fluorescent diazo ring compound (AZO(550)) that is expected to form when the nonfluorescent NO(550) reacts with cellular NO, and compared its cellular distribution with that of NO(550).

CONCLUSION

NO(550) is a promising agent for imaging NO at baseline and in response to pharmacological agents that modulate its levels.

The organic air pollutant cumene hydroperoxide interferes with NO antioxidant role in rehydrating lichen

Organic pollutants effects on lichens have not been addressed. Rehydration is critical for lichens, a burst of free radicals involving NO occurs. Repeated dehydrations with organic pollutants could increase oxidative damage. Our aim is to learn the effects of cumene hydroperoxide (CP) during lichen rehydration using Ramalina farinacea (L.) Ach., its photobiont Trebouxia spp. and Asterochloris erici. Confocal imaging shows intracellular ROS and NO production within myco and phycobionts, being the chloroplast the main source of free radicals. CP increases ROS, NO and lipid peroxidation and reduces chlorophyll autofluorescence, although photosynthesis remains unaffected. Concomitant NO inhibition provokes a generalized increase of ROS and a decrease in photosynthesis. Our results suggest that CP induces a compensatory hormetic response in Ramalina farinacea that could reduce the lichen's antioxidant resources after repeated desiccation-rehydration cycles. NO is important in the protection from CP.

Seminaphthofluorescein-based fluorescent probes for imaging nitric oxide in live cells

Fluorescent turn-on probes for nitric oxide based on seminaphthofluorescein scaffolds were prepared and spectroscopically characterized. The Cu(II) complexes of these fluorescent probes react with NO under anaerobic conditions to yield a 20-45-fold increase in integrated emission. The seminaphthofluorescein-based probes emit at longer wavelengths than the parent FL1 and FL2 fluorescein-based generations of NO probes, maintaining emission maxima between 550 and 625 nm. The emission profiles depend on the excitation wavelength; maximum fluorescence turn-on is achieved at excitations between 535 and 575 nm. The probes are highly selective for NO over other biologically relevant reactive nitrogen and oxygen species including NO(3)(-), NO(2)(-), HNO, ONOO(-), NO(2), OCl(-), and H(2)O(2). The seminaphthofluorescein-based probes can be used to visualize endogenously produced NO in live cells, as demonstrated using Raw 264.7 macrophages.

Fungal-associated NO is involved in the regulation of oxidative stress during rehydration in lichen symbiosis

BACKGROUND

Reactive oxygen species (ROS) are normally produced in respiratory and photosynthetic electron chains and their production is enhanced during desiccation/rehydration. Nitric oxide (NO) is a ubiquitous and multifaceted molecule involved in cell signaling and abiotic stress. Lichens are poikilohydrous organisms that can survive continuous cycles of desiccation and rehydration. Although the production of ROS and NO was recently demonstrated during lichen rehydration, the functions of these compounds are unknown. The aim of this study was to analyze the role of NO during rehydration of the lichen Ramalina farinacea (L.) Ach., its isolated photobiont partner Trebouxia sp. and Asterochloris erici (Ahmadjian) Skaloud et Peksa (SAG 32.85 = UTEX 911).

RESULTS

Rehydration of R. farinacea caused the release of ROS and NO evidenced by the fluorescent probes DCFH₂-DA and DAN respectively. However, a minimum in lipid peroxidation (MDA) was observed 2 h post-rehydration. The inhibition of NO in lichen thalli with c-PTIO resulted in increases in both ROS production and lipid peroxidation, which now peaked at 3 h, together with decreases in chlorophyll autofluorescence and algal photobleaching upon confocal laser incidence. Trebouxia sp. photobionts generate peaks of NO-endproducts in suspension and show high rates of photobleaching and ROS production under NO inhibition which also caused a significant decrease in photosynthetic activity of A. erici axenic cultures, probably due to the higher levels of photo-oxidative stress.

CONCLUSIONS

Mycobiont derived NO has an important role in the regulation of oxidative stress and in the photo-oxidative protection of photobionts in lichen thalli. The results point to the importance of NO in the early stages of lichen rehydration.

Tunable design strategy for fluorescence probes based on 4-substituted BODIPY chromophore: improvement of highly sensitive fluorescence probe for nitric oxide

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is a well-known fluorophore, with a high molar extinction coefficient and high fluorescence quantum efficiency (Phi(fl)). Furthermore, its structure can be modified to change its excitation and emission wavelengths. However, little work has been done on the structural modification of fluorines at the B-4 position with other functional groups. We synthesized 4-methoxy-substituted BODIPY derivatives in satisfactory yields, and found that they exhibited improved solubility in aqueous solution. Moreover, their oxidation and reduction potentials were greatly decreased without any change in their absorbance and fluorescence properties. These features of 4-substituted BODIPYs may be useful for developing novel fluorescence probes based on the intramolecular photoinduced electron transfer (PeT) mechanism, because it is possible to optimize the PeT process precisely by modulating the electrochemical properties of the fluorophore. The value of this approach is exemplified by its application to the development of a highly sensitive and pH-independent fluorescence probe for nitric oxide.

Nitric Oxide-Induced Fluorescence Enhancement by Displacement of Dansylated Ligands from Cobalt

The cobalt complexes [Co(Ds-AMP)(2)] (1) and [Co(Ds-AQ)(2)] (2), where Ds-AMP and Ds-AQ are the conjugate bases of dansyl aminomethylpyridine (Ds-HAMP) and dansyl aminoquinoline (Ds-HAQ), respectively, were synthesized in two steps as fluorescence-based nitric oxide (NO) sensors and characterized by X-ray crystallography. The fluorescence of the two complexes was significantly quenched in CH(3)CN or CH(3)OH compared to that of the free Ds-HAMP or Ds-HAQ ligands. Addition of NO to a CH(3)CN solution of 1 or 2 enhanced the integrated fluorescence emission by factors of 2.1(+/-0.3) or 3.6(+/-0.4) within 35 or 20 min, respectively. Introduction of NO to methanolic solutions of the complexes similarly increased the fluorescence by 1.4(+/-0.1) for 1 or 6.5(+/-1.4) for 2 within 1 h. These studies demonstrate that 1 and 2 can monitor the presence of NO with turn-on emission and that their fluorescence responses are more rapid than those of previously reported cobalt systems in coordinating solvents such as CH(3)CN and CH(3)OH. (1)H NMR and IR spectroscopic data revealed the formation of a [Co(NO)(2)](10) cobalt-dinitrosyl adduct, with concomitant dissociation of one ligand from the cobalt center, as the metal-containing product of the NO reactions, a result indicating NO-induced ligand release to be the cause of the fluorescence increase.

Nitric oxide-dependent long-term potentiation revealed by real-time imaging of nitric oxide production and neuronal excitation in the dorsal horn of rat spinal cord slices

Nitric oxide (NO) is thought to be involved in the central mechanism of hyperalgesia and allodynia at the spinal level. Recently, we reported that NO played an important role in the induction of long-term potentiation (LTP) of synaptic strength in spinal dorsal horn, which is believed to underlie hyperalgesia and allodynia. In this study, to elucidate the relationship of NO to LTP in spinal dorsal horn, we measured the spatiotemporal distribution of NO signal with the NO-sensitive dye, DAR-4M, and neuronal excitation with the voltage-sensitive dye, RH482, in rat spinal cord slices, elicited by dorsal root stimulation. In superficial dorsal horn, neuronal excitation evoked by C fiber-activating dorsal root stimulation was potentiated for more than 2 h after low-frequency conditioning stimulation (LFS, 240 pulses at 2 Hz for 2 min). In the same slices that exhibited LTP, NO was produced and distributed in the superficial dorsal horn during the delivery of LFS, and the amplitude of LTP and amount of NO production showed close correlation from slice to slice. LTP and production of NO were inhibited in the presence of the NO synthase inhibitors and an inhibitor of heme oxygenase, the synthetic enzyme for carbon monoxide (CO). These results suggest that production and distribution of NO is necessary for the induction of LTP in spinal dorsal horn, and that CO contributes to the LTP induction and NO production by LFS.

Use of Fluorescence Probes for Detection of Reactive Nitrogen Species: A Review

The biological and toxicological effects that have been attributed to reactive nitrogen species (RNS) are increasingly stirring the scientific inquisitiveness about the molecular mechanisms involved. However, RNS present some characteristics that complicate their detection, namely their short lifetime and the normal presence of a variety of endogenous compounds capable of reacting with these reactive species, when the studies are performed in biological matrices. The development of methodologies capable of circumvent these difficulties is thus of fundamental importance. Fluorescence probes are particularly important due to their high sensibility and usefulness in temporal and spatial monitoring of RNS, particularly in microanalysis conditions in biological media akin to cells or tissues. In the present review is given an account of the fluorescence probes that have been used for detection of nitric oxide (*NO), peroxynitrite anion (ONOO-), as well as of some of its derivatives in biological and nonbiological media.

Application of 4,5-diaminofluorescein to reliably measure nitric oxide released from endothelial cells in vitro

Here we describe in more depth the previously published application of the fluorescent probe 4,5-diaminofluorescein (DAF-2) in order to reliably measure low levels of nitric oxide (NO) as released from human endothelial cells in vitro. The used approach is based on the following considerations a) use low concentrations of DAF-2 (0.1 µM) in order to reduce the contribution of DAF-2 auto-fluorescence to the measured total fluorescence, and b) subtract the DAF-2 auto-fluorescence from the measured total fluorescence. The advantage of this method is the reliable quantification of NO in a biological system in the nanomolar range once thoroughly validated. Here we focus in addition to the previous publication (Leikert et al., FEBS Lett 2001, 506:131-134) on aspects of validation procedures as well as limitations and pitfalls of this method.

Detection of reactive oxygen and nitrogen species in tissues using redox-sensitive fluorescent probes

The take-home message of this chapter is that the fluorescent probes for ROS and RNS have great potential in improving our understanding of redox behavior within cells and tissues. However, data obtained from studies using these probes must be expressed in the context of the limitations of the chemistry of the probes in the cellular microenvironment, which may change under different conditions, such as cell stress or injury. In most cases, as suggested, results should be described in a general context of reflecting an increase in oxidizing reactions within the cell and not as a quantitative measure of the production of a specific oxidant species. It is highly recommended that results be verified, when possible, with alternative fluorescent probes or preferably using alternative methods, such as electron spin resonance or other newly emerging technology.

Nitric oxide ameliorates hydrophobic bile acid-induced apoptosis in isolated rat hepatocytes by non-mitochondrial pathways

Hydrophobic bile acids are toxic to isolated rat hepatocytes by mechanisms involving mitochondrial dysfunction and oxidative stress. In the current study we examined the role of nitric oxide (NO), a potential mediator of apoptosis, during bile acid-induced apoptosis. Freshly isolated rat hepatocytes and hepatic mitochondria generated NO and peroxynitrite (ONOO(-)) in a concentration- and time-dependent manner when exposed to the toxic bile salt glycochenodeoxycholate (GCDC) (25-500 microm), which was prevented by the nitric-oxide synthase (NOS) inhibitors N(G)-monomethyl-N-arginine monoacetate (l-NMMA) and 1400W. Relationships between hepatocyte NO production and apoptosis were examined by comparing the effects of NOS inhibitors with other inhibitors of GCDC-induced apoptosis. Inhibitors of caspases 8 and 9, the mitochondrial permeability transition blocker cyclosporin A, and the antioxidant idebenone reduced NO generation and apoptosis in GCDC-treated hepatocytes. In contrast, NOS inhibitors had no effect on GCDC-induced apoptosis despite marked reduction of NO and ONOO(-). However, treatment with the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate [N-(-aminoethyl)N-(2-hydroxy-2-nitrohydrazino)-1,2-ethylenediamine) inhibited apoptosis and caspase 3 activity while significantly elevating NO levels above GCDC-stimulated levels. Neither NO donors nor NOS inhibitors affected GCDC-induced mitochondrial permeability transition or cytochrome c release from liver mitochondria or GCDC-induced mitochondrial depolarization from isolated hepatocytes, suggesting that NO inhibits bile acid-induced hepatocyte apoptosis by a non-mitochondrial-dependent pathway. In conclusion, whereas NO produced from GCDC-treated hepatocytes neither mediates nor protects against bile acid-induced apoptosis, higher levels of NO inhibit GCDC-induced hepatocyte apoptosis by caspase-dependent pathways.

Nitric oxide regulates smooth-muscle-specific myosin heavy chain gene expression at the transcriptional level-possible role of SRF and YY1 through CArG element

Nitric oxide (NO) plays an important role in vascular regulation through its vasodilatory, antiatherogenic, and antithrombotic properties. NO inhibits platelet adhesion and aggregation and modulates smooth muscle cell (SMC) proliferation and migration. In animals with experimentally induced vascular injury, ec-NOS gene transfection not only restored NO production to normal levels but also increased vascular reactivity of the injured vessels. However, it is unclear whether NO regulates smooth-muscle-specific gene expression. We report here that addition of PDGF-BB to vascular smooth muscle cells suppressed SM-MHC expression but treatment with the NO donors FK409 and SNAP restored SM-MHC mRNA/protein expression. In vitro transfection and subsequent CAT assays demonstrated that exogenous NO can restore PDGF-BB-induced suppression of SM-MHC promoter activity. Promoter deletion analysis revealed that a CArG-3 box located at -1276 bp in the SM-MHC promoter was important for NO-dependent promoter regulation and as well as high level promoter activity. Gel mobility shift assays showed that CArG-3 contained the SRF binding site and a binding site for YY1, a nuclear factor which acts as a negative regulator on muscle-specific promoters. Interestingly, NO donor FK409 reduced YY1 binding to the CArG-3 element but increased SRF binding, suggesting that these two factors bind competitively to the overlapping sites. We also found that mutation to the YY1 binding site in the CArG-3 element resulted in a loss of PDGF-BB-induced suppression of the SM-MHC promoter activity. These findings indicate that NO regulates SM-MHC gene expression at the transcriptional level at least partially through the regulation of transcription factor binding activities on the CArG element. Thus we propose that NO plays a positive role in maintaining the differentiated state of VSMCs.

Direct evidence of nitric oxide presence within mitochondria

Nitric oxide (NO) has been implicated in the modulation of mitochondrial respiration, membrane potential, and subsequently in apoptosis. Although the presence of a mitochondrial NO synthase (mtNOS) has been described, there is no direct evidence in vivo of the presence of NO within mitochondria. It was the aim of this study to demonstrate the in vivo production of NO within mitochondria. Using the novel fluorometric NO detection system, 4,5-diaminofluorescein diacetate (DAF-2/DA), we observed the presence of NO production in PC12 and COS-1 cells by conventional and confocal fluorescence microscopy. Part of the overall NO signal was colocalized within a subpopulation of mitochondria, labeled with the potential-dependent probe MitoTracker red. These findings demonstrate for the first time that the subcellular distribution of NO production is consistent with the presence of a mitochondrial NOS. Our results provide a new tool to directly study the modulatory role of NO in mitochondrial respiration and membrane potential, in vivo.

Bio-imaging of nitric oxide-producing neurones in slices of rat brain using 4,5-diaminofluorescein

4,5-Diaminofluorescein (DAF-2) was used to identify individual nitric oxide (NO)-producing neurones in brain slices in vitro. Coronal slices of midbrain or hippocampus, 300 microm thick from young adult rats, were incubated for 30 min in 1 microM DAF-2 diacetate (DAF-2 DA) and maintained in ACSF at 33 degrees C. Illumination at 450-490 nm revealed punctate fluorescence in neurones in the lateral tegmental nucleus, dorsal raphe nucleus, dorsolateral periaqueductal grey matter, deep collicular layers and cortical areas. Neurones in the hippocampal pyramidal cell layer, molecular layer of the dentate gyrus and the hilus fluoresced also. The fluorescence was abolished by pre-incubation of slices with L-NAME (100 microM-1 mM), the inhibitor of constitutive nitric oxide synthase (NOS), but not by D-NAME (100 microM) or L-NIL (5-50 microM), an inhibitor of inducible NOS. In some superficially located arterioles, there were small regions of bright fluorescence close to the outer smooth muscle wall and diffuse fluorescence within the adjacent smooth muscle cells. A diffuse fluorescence was also seen in some superficially located capillaries. Basal production of NO was not seen within deeper blood vessels. DAF-2 DA offers a sensitive indicator for visualising basal production of NO with high spatial resolution and could provide a means of identifying NOS-containing neurones in brain slices in vitro prior to neurophysiological study.

Single-cell analyses of nitrergic neurons in simple nervous systems

Understanding the role of the gaseous messenger nitric oxide (NO) in the nervous system is complicated by the heterogeneity of its nerve cells; analyses carried out at the single cell level are therefore important, if not critical. Some invertebrate preparations, most especially those from the gastropod molluscs, provide large, hardy and identified neurons that are useful both for the development of analytical methodologies and for cellular analyses of NO metabolism and its actions. Recent modifications of capillary electrophoresis (CE) allow the use of a small fraction of an individual neuron to perform direct, quantitative and simultaneous assays of the major metabolites of the NO-citrulline cycle and associated biochemical pathways. These chemical species include the products of NO oxidation (NO2-/NO3-), l-arginine, l-citrulline, l-ornithine, l-argininosuccinate, as well as selected NO synthase inhibitors and cofactors such as NADPH, biopterin, FMN and FAD. Diverse cotransmitters can also be identified in the same nitrergic neuron. The sensitivity of CE methods is in the femtomole to attomole range, depending on the species analysed and on the specific detector used. CE analysis can be combined with prior in vivo electrophysiological and pharmacological manipulations and measurements to yield multiple physiological and biochemical values from single cells. The methodologies and instrumentation developed and tested using the convenient molluscan cell model can be adapted to the smaller and more delicate neurons of other invertebrates and chordates.