Nitric Oxide Uptake Research Articles

Xylophagous termites: A potential sink for atmospheric nitrous oxide

To provide a better understanding of soil–atmosphere gas exchange processes, this study describes the atmospheric nitrous oxide (N2O) uptake by xylophagous termites and the biological process involved. The N2O consumption rates of three xylophagous termite species (Hodotermes mossambicus, Nasutitermes voeltzkowi and Hodotermopsis sjoestedti) were determined in incubation vials with ambient, artificially enhanced N2O concentrations in the headspace. Live individuals of the three termite species significantly decreased N2O concentrations (88%) in the headspace of the vials after 24 h incubation in the dark. The acetylene reduction assay method applied to N. voeltzkowi, a xylophagous termite species, showed a decrease in N2O uptake in acetylene-treated individuals, indicating the potential involvement of termite gut denitrifying microbes. The N2 formed is potentially subjected to assimilation via nitrogenase reductase into termite biomass through biological fixation as demonstrated by the reduction of acetylene to ethylene at an average rate of 18.21 ± 1.34 nmol C2H4 g−1 dw d−1. Further studies should focus on measurements of N2O-reductase (nosZ) gene activity in termite guts to gain a better understanding of the N2O reduction process in xylophagous termite species.

Measurement and Simulation of Nitric Oxide Uptake by Hemoglobin-Containing Vesicles and Red Blood Cells

Measurement and Simulation of Nitric Oxide Uptake by Hemoglobin-Containing Vesicles and Red Blood Cells

Mechanisms of Slower Nitric Oxide Uptake by Red Blood Cells and Other Hemoglobin-containing Vesicles

Nitric oxide (NO) acts as a smooth muscle relaxation factor and plays a crucial role in maintaining vascular homeostasis. NO is scavenged rapidly by hemoglobin (Hb). However, under normal physiological conditions, the encapsulation of Hb inside red blood cells (RBCs) significantly retards NO scavenging, permitting NO to reach the smooth muscle. The rate-limiting factors (diffusion of NO to the RBC surface, through the RBC membrane or inside of the RBC) responsible for this retardation have been the subject of much debate. Knowing the relative contribution of each of these factors is important for several reasons including optimization of the development of blood substitutes where Hb is contained within phospholipid vesicles. We have thus performed experiments of NO uptake by erythrocytes and microparticles derived from erythrocytes and conducted simulations of these data as well as that of others. We have included extracellular diffusion (that is, diffusion of the NO to the membrane) and membrane permeability, in addition to intracellular diffusion of NO, in our computational models. We find that all these mechanisms may modulate NO uptake by membrane-encapsulated Hb and that extracellular diffusion is the main rate-limiting factor for phospholipid vesicles and erythrocytes. In the case of red cell microparticles, we find a major role for membrane permeability. These results are consistent with prior studies indicating that extracellular diffusion of several gas ligands is also rate-limiting for erythrocytes, with some contribution of a low membrane permeability.

Humphry Davy

Humphry Davy

Nitrogen dynamics at undisturbed and burned Mediterranean shrublands of Salento Peninsula, Southern Italy

Fire is a major disturbance in shrubland ecosystems of the Mediterranean basin, with high potential to alter ecosystem nitrogen (N) stocks and N cycling. However, postfire effects on gross rates of soil N turnover (ammonification, nitrification, microbial immobilization, denitrification) have rarely been investigated. We determined gross rates of N turnover including nitrous oxide fluxes and dinitrogen emissions in the mineral soil of unburned and burned shrublands of Southern Italy 6 months after a natural fire. In soil of burned plots, both gross ammonification and gross nitrification were significantly higher than in soil of unburned plots (2.2 ± 0.3 versus 0.6 ± 0.1 mg N kg−1 sdw day−1 for ammonification and 1.1 ± 0.1 versus 0.5 ± 0.1 mg N kg−1 sdw day−1 for nitrification). Microbial immobilization, in particular of nitrate, could not compensate for the increase in inorganic N production, therefore soil nitrate concentrations were considerably higher at the burned plots. Soil microbial biomass carbon and nitrogen concentrations were significantly lower in soils of burned plots than in soils of unburned plots. Dinitrogen was the dominant end product of denitrification and emitted at higher rates from the unburned plots than from the burned plots (0.094 ± 0.003 versus 0.004 ± 0.002 mg N kg−1 sdw day−1, while there was no net nitrous oxide flux (burned plots) or slight net nitrous oxide uptake (control plots). These results show that postfire patterns of gross N turnover in soil can exhibit a significant reduction of both microbial N retention and N gas losses via denitrification.

Neglecting sinks for N2O at the earth's surface: does it matter?

The uptake of nitrous oxide (N2O) occurs at the surface of the earth both in terrestrial and aquatic systems. This uptake is usually neglected in N2O budget studies. In this article, we discuss the likeliness of N2O uptake in different systems. These systems include soils as well as groundwater systems, riparian zones and surface waters. We address the possible consequences of ignoring surface sinks for N2O in global budgets as well as in national emission inventories. Our estimated surface sink is relatively small compared to the estimates of the present-day global emissions. Neglecting a possible surface sink of N2O may, therefore, not have major consequences for atmospheric budget studies on the global scale. However, locally, N2O uptake may be considerable. For countries with large areas prone to N2O uptake, neglecting this sink in national budgets may have important consequences.

The effect of posture-induced changes in peripheral nitric oxide uptake on exhaled nitric oxide

Airway and alveolar NO contributions to exhaled NO are being extracted from exhaled NO measurements performed at different flow rates. To test the robustness of this method and the validity of the underlying model, we deliberately induced a change in NO uptake in the peripheral lung compartment by changing body posture between supine and prone. In 10 normal subjects, we measured exhaled NO at target flows ranging from 50 to 350 ml/s in supine and prone postures. Using two common methods, bronchial NO production [Jaw(NO)] and alveolar NO concentration (FANO) were extracted from exhaled NO concentration vs. flow or flow(-1) curves. There was no significant Jaw(NO) difference between prone and supine but a significant FANO decrease from prone to supine ranging from 23 to 33% depending on the method used. Total lung capacity was 7% smaller supine than prone (P = 0.03). Besides this purely volumetric effect, which would tend to increase FANO from prone to supine, the observed degree of FANO decrease from prone to supine suggests a greater opposing effect that could be explained by the increased lung capillary blood volume (V(c)) supine vs. prone (P = 0.002) observed in another set of 11 normal subjects. Taken together with the relative changes of NO and CO transfer factors, this V(c) change can be attributed mainly to pulmonary capillary recruitment from prone to supine. Realistic models for exhaled NO simulation should include the possibility that a portion of the pulmonary capillary bed is unavailable for NO uptake, with a maximum capacity of the pulmonary capillary bed in the supine posture.

Closed-form solutions for the optimum equivalence of first-order compartmental models and their implications for classical models of closed-circuit anesthesia

Given a function that describes the uptake of a substance into the body with time, an analytical technique is described which transforms that function into a model of parallel first-order compartments that converges to the same uptake profile as the number of compartments is increased. The fitting of the compartmental model to the given uptake function is optimized to minimize the squared error. A necessary condition of the analytical method is that the uptake function be capable of being successively integrated at least as many times as the number of desired compartments. The uptake function should also be monotonically decreasing as all parallel first-order compartment models predict monotonically decreasing uptake. We applied this technique and ascertained the compartmental structure of the Severinghaus relationship, a longstanding observation in the field of clinical anesthesia that the uptake of nitrous oxide follows an inverse-square-root of time profile. The Severinghaus relationship is numerically poorly behaved at a time of zero elapsed minutes, predicting an instantaneously infinite uptake. Nevertheless, modeling of the first minute of anesthesia is necessary for characterizing the initial induction of anesthesia and methods of maintaining closed-circuit anesthesia such as the unit dose method. Using solely analytical methods, solutions for the compartmental properties of a mammillary model that matches the Severinghaus relationship for any expressed time interval are produced. These properties are compared to currently accepted values for the uptake of nitrous oxide. When matched to the Severinghaus relationship in the range of 0–100 min with a three-compartment model, we identified time constants of 0.28, 4.69 and 33.49 min with associated apparent volumes of 1.44, 2.14 and 7.97 l, respectively. The time constants in particular contrast to our earlier findings for the range of 1–100 min (1.46, 7.41 and 42.0 min). Our earlier findings were well matched to published time constants for tissues in classical pharmacokinetic models for volatile uptake. Consequently, we conclude that rigid adherence to the Severinghaus relationship from a time of zero minutes may lead to the over-administration of anesthetic agent due to an implicit mischaracterization of the relevant compartmental properties.

Platelets in Storage: Altered S-Nitrosothiol Metabolism and Decreased Responsiveness May Be Related.

Under normal physiologic conditions, platelets circulate in an inactivated state and require only minimal stimulation ensuring their immediate availability for hemostasis. Previous research has shown that during platelet pheresis and storage, platelets undergo early activation resulting in expression of the surface activation marker CD62, release of α granule contents, and a decrease in inducible activation. In addition to regulating vascular tone, nitric oxide (NO) groups in plasma may provide tonic inhibition to circulating platelets thereby preventing the inappropriate adhesion and aggregation seen in stored platelets. S-Nitrosothiols (RSNOs) may serve as a reservoir for nitric oxide (NO) in the normal circulation. We hypothesize that platelets are prematurely activated during the process of apheresis in part due to the lack of RSNOs in the microenvironment during collection and storage. Furthermore, RSNO metabolism by stored platelets is changed by the process of apheresis itself. To test this hypothesis, we monitored the activation status of platelets using CD62 flow cytometry and quantified intracellular NO content and uptake using the fluorescence probe diaminodifluorofluorescein diacetate (DAF-FM DA). Both measurements were made on freshly isolated platelets (Fl-Plts) and on apheresis platelets (A-Plts). In addition, we employed these techniques to evaluate the responsiveness of Fl-Plts and A-Plts to agonists [thrombin receptor activating peptide (TRAP), ADP, and collagen] and to NO-donating molecules after varying storage times. In preliminary studies we have found that Fl-Plts bind RSNOs and demonstrate steroselectivity in their degree of uptake. Fl-Plts incubated with L-RSNOs produce over 2-fold the fluorescence compared to Fl-Plts incubated with D-RSNOs. A-Plts lose this stereoselectivity in RSNO uptake following the collection and storage process. We have also found that A-Plts have up to a 10-fold increase in uptake of nitric oxide from RSNOs compared to Fl-Plts. This significant increase and loss of stereoselectivity in RSNO uptake in A-Plts correlates with the loss of inducible activation over storage time. These data suggest RSNO metabolism in platelets is fundamentally altered during apheresis, collection, and storage and provides a novel target with therapeutic potential for further investigation into the loss of platelet function during storage.

Diminished Alveolar Microvascular Reserves in Type 2 Diabetes Reflect Systemic Microangiopathy

OBJECTIVE—Alveolar microvascular function is moderately impaired in type 1 diabetes, as manifested by restriction of lung volume and diffusing capacity (DLCO). We examined whether similar impairment develops in type 2 diabetes and defined the physiologic sources of impairment as well as the relationships to glycemia and systemic microangiopathy.RESEARCH DESIGN AND METHODS—A cross-sectional study was conducted at a university-affiliated diabetes treatment center and outpatient diabetes clinic, involving 69 nonsmoking type 2 diabetic patients without overt cardiopulmonary disease. Lung volume, pulmonary blood flow (Q̇), DLCO, membrane diffusing capacity (measured from nitric oxide uptake [DLNO]), and pulmonary capillary blood volume (VC) were determined at rest and exercise for comparison with those in 45 healthy nonsmokers as well as with normal reference values.RESULTS—In type 2 diabetic patients, peak levels of oxygen uptake, Q̇ and DLCO, DLNO, and VC at exercise were 10–25% lower compared with those in control subjects. In nonobese patients (BMI <30 kg/m2), reductions in DLCO, DLNO, and VC were fully explained by the lower lung volume and peak Q̇, but these factors did not fully explain the impairment in obese patients (BMI >30 kg/m2). The slope of the increase in VC with respect to Q̇ was reduced ∼20% in patients regardless of BMI, consistent with impaired alveolar-capillary recruitment. Functional impairment was directly related to A1C level, retinopathy, neuropathy, and microalbuminuria in a sex-specific manner.CONCLUSIONS—Alveolar microvascular reserves are reduced in type 2 diabetes, reflecting restriction of lung volume, alveolar perfusion, and capillary recruitment. This reduction correlates with glycemic control and extrapulmonary microangiopathy and is aggravated by obesity.

The rate of alveolar‐capillary uptake of sevoflurane and nitrous oxide following anaesthetic induction

The rate of anaesthetic gas uptake from the breathing system has been extensively measured, but this does not reflect the true rate of early gas uptake by pulmonary blood, which drives inhalational induction of anaesthesia. In eight patients undergoing coronary bypass surgery, we measured the rate of alveolar-capillary uptake of anaesthetic gases up to 30 min following introduction of 0.5% sevoflurane and 33% nitrous oxide using the reverse Fick method, in which blood partial pressures were measured using a headspace equilibration technique. Simultaneous measurements of gas uptake from the breathing system were made by indirect calorimetry. Measured rates of sevoflurane and nitrous oxide uptake from the breathing system agreed well with previously described formulae when adjusted for inspired concentration. The time course of alveolar-capillary gas uptake followed a characteristic rising curve peaking at 3-4 min and then exponentially declining, and for nitrous oxide was significantly higher than previously estimated.

An Integrated Mathematical and Experimental Model for Nitric Oxide uptake by Red Blood Cells

Endothelium‐derived nitric oxide (NO) is a potent vasodilator despite the presence of hemoglobin (Hb) encapsulated in red blood cells (RBC) which has high affinity for scavenging NO (k~ 107 M−1 s−1). NO uptake by RBC‐Hb is reported to be several orders lesser than that of free Hb. Reduced uptake by RBC encapsulated Hb is attributed to several diffusional resistances for NO to react with Hb including extracellular resistance, cell free layer resistance near the vessel wall, resistance in unstirred layer surrounding RBCs and resistance by RBC membrane. The extent of contribution from each diffusional layer towards reduced NO uptake by RBCs is under intense investigation. We developed a novel stirred bioreactor with a headspace to maintain controlled NO concentrations. Using this bioreactor along with an electrochemical NO sensor, we measured the bulk NO concentration in RBC suspensions DI water for various NO concentrations in the bioreactor headspace. We developed a steady state one dimensional mathematical model representing NO biotransport using the data obtained from above experiments to predict NO concentration profile and to determine the role of extracellular diffusional resistance, resistance offered by unstirred layer surrounding RBCs and resistance offered by RBC membrane. This integrated analysis will provide quantitative information about NO_RBC interaction parameters.

Tissue Factor Coagulant Function Is Enhanced by Protein-disulfide Isomerase Independent of Oxidoreductase Activity

Protein-disulfide isomerase (PDI) switches tissue factor (TF) from coagulation to signaling by targeting the allosteric Cys186-Cys209 disulfide. Here, we further characterize the interaction of purified PDI with TF. We find that PDI enhances factor VIIa-dependent substrate factor X activation 5-10-fold in the presence of wild-type, oxidized soluble TF but not TF mutants that contain an unpaired Cys186 or Cys209. PDI-accelerated factor Xa generation was blocked by bacitracin but not influenced by inhibition of vicinal thiols, reduction of PDI, changes in redox gradients, or covalent thiol modification of reduced PDI by N-ethylmaleimide or methyl-methanethiosulfonate, which abolished PDI oxidoreductase but not chaperone activity. PDI had no effect on fully active TF on either negatively charged phospholipids or in activating detergent, indicating that PDI selectively acts upon cryptic TF to facilitate ternary complex formation and macromolecular substrate turnover. PDI activation was reduced upon mutation of TF residues in proximity to the macromolecular substrate binding site, consistent with a primary interaction of PDI with TF. PDI enhanced TF coagulant activity on microvesicles shed from cells, suggesting that PDI plays a role as an activating chaperone for circulating cryptic TF.

NO Break-Ins at Water Gate

Nitric oxide (NO) is a gaseous free radical that functions as an endogenous mediator in diverse biological effects in numerous tissues. In the kidney and vasculature, these processes include the control of systemic and microvascular tone, the glomerular microcirculation, renal sodium excretion, and inflammatory responses in the glomerulus and tubulointerstitium, among many others.1 NO also impacts the renin–angiotensin and eicosanoid systems, endothelin, cytokines, and other key regulators of inflammation. Because of its potent chemical reactivity, high diffusibility, and the fact that, unlike most endogenous chemical signals, it cannot be stored or secreted, NO production by NO synthases is under complex, tight control to dictate specificity of its signaling and to limit toxicity to other cellular components. These controls serve to govern the timing, magnitude, and spatial distribution of NO release, and, in turn, specify the input signals that activate NO release and the effector functions of the molecule to target specific proteins. The biological role of NO as an inter- and intracellular messenger molecule is greatly dependent on its effective concentration and bioavailability at sites of action. As a hydrophobic gas, NO has traditionally been thought to traverse freely across cell membranes without the need for a specific transport protein to facilitate diffusion. It is also known that NO may accumulate in cellular lipids and preferentially interact with molecules in lipid environments. Since cellular entry of NO has generally been regarded to be near diffusion-limited, many of the reactions of NO are thought to depend on the rate of collision between NO and its target molecules or functional groups. Proteins that are structurally or …

Persisting concentrating and second gas effects on oxygenation during N2O anaesthesia

Theoretical modelling predicts that the concentrating effect of nitrous oxide (N2O) uptake on alveolar oxygenation is a persisting phenomenon at typical levels of ventilation - perfusion (V/Q) inhomogeneity under anaesthesia. We sought clinical confirmation of this in 20 anaesthetised patients. Arterial oxygen pressure (P(aO2)) was measured after a minimum of 30 min of relaxant general anaesthesia with an inspired oxygen (F(I O2)) of 30%. Patients were randomly allocated to two groups. The intervention group had N2O introduced following baseline blood gas measurements, and the control group continued breathing an identical F(I O2) in nitrogen (N2). The primary outcome variable was change in P(aO2). Mean (SD) in P(aO2) was increased by 1.80 (1.80) kPa after receiving a mean of 47.5 min of N2O compared with baseline conditions breathing O2/N2 (p = 0.01). This change was significantly greater (p = 0.03) than that in the control group: + 0.09 (1.37) kPa, p = 0.83 and confirms the presence of significant persisting concentrating and second gas effects.

Superoxide negatively modulates angiotensin II‐elicited calcium response via increasing nitric oxide uptake in vascular smooth muscle cells

Angiotensin II (Ang II), a multifunctional hormone, increases cytosolic calcium concentration via inositol 1,4,5-trisphosphate (IP3) signal pathway in vascular smooth muscle cells (SMCs), resulting in cell contraction. In addition, Ang II can also raise the level of intracellular superoxide (O2−) via activation of NAD(P)H oxidase. Nitric oxide (NO), on the other hand, has been shown to inhibit mobilization of IP3-gated calcium channel through increased intracellular cGMP. We have previously demonstrated that O2− determines NO uptake rate by vascular SMCs. Thus, it is likely that Ang II may use O2− to increase the SMC-NO uptake rate, which may in turn serve as a negative feedback circuitry of calcium response. To demonstrate the role of O2− in the Ang II-elicited calcium response, first we showed that the calcium response is in an Ang II dependent manner using fluorescent dye, Fura-2, with a fluorescence spectrophotometer. After verifying the assay for calcium responses, we had SMCs compete with oxyhemoglobin for NO during the Ang II challenge. Increasing Ang II-enhanced intracellular O2− content by pretreatment of SMCs with NADPH or SOD inhibitors decreases the Ang II-elicited calcium response. In contrary, pretreatment of tiron, a O2− scavenger, increases the Ang II-stimulated calcium response. Taken together, our results demonstrate that O2− in vascular SMCs, at least in a certain range of concentrations, modulates negatively the Ang II-elicited calcium response via increasing the SMC-NO uptake rate, suggesting a beneficial role of O2− in SMCs in the blood vessel response.

Physiologically precise simulation of multiple lung gas exchange during anaesthesia by simultaneous gas infusion and extraction

A lung gas exchange simulator was tested which produces simultaneous uptake and/or elimination of multiple gases by an artificial test lung with physiologically realistic gas expired and exhaust gas flows, using a combination of infusion of diluting/enriching gases into the lung with lung gas extraction. A deterministic algorithm is incorporated which calculates required gas infusion and extraction flow rates for any set of possible target gas exchange values with any given set of fresh gas flows and concentrations. Six different scenarios were simulated, comprising a range of gas exchange values for each gas species which lie within a physiologically realistic range for anaesthetized patients. For each of these experiments the system was tested for 15 consecutive measurements over 25 min by measurement of gas exchange in the system using the Haldane transformation. Results: the mean bias and standard error of the mean bias (SE, in parentheses) relative to the target value was: +0.001 (0.002) l min−1 for O2 uptake, −0.002 (0.005) l min−1 for CO2 production, −0.001 (0.002) l min−1 for uptake of nitrous oxide and +0.3 (0.1) ml min−1 for uptake of a volatile anaesthetic agent (isoflurane). The confidence limits of the mean bias were within 5% of the target value for all gases and scenarios with the exception of those where a low uptake of anaesthetic gas was specified. The confidence limits of the mean bias for the lower uptakes of isoflurane were within 10% of the target value for these scenarios and within 15% for the low uptake of N2O. Good accuracy and precision of this approach to lung gas exchange simulation were demonstrated, resulting in a versatile simulator.

Superoxide determines nitric oxide uptake rate by vascular smooth muscle cells

Nitric oxide (NO) is generated in endothelial cells, which diffuses to vascular smooth muscle cells (SMCs), activates soluble guanylyl cyclase, and leads to blood vessel dilation. However, this scenario does not explain how SMCs are capable of competing with erythrocytic hemoglobin for NO in vivo. Here, we have developed a competition experiment to determine the NO uptake rate by SMCs and demonstrated that the SMC-NO uptake rate is positively dependent on intracellular superoxide levels. In addition, the superoxide-elicited NO influx is able to enhance cGMP production in SMCs. Our findings imply that vascular SMCs, in vivo, may use superoxide to compete with erythrocytic hemoglobin for NO and obtain the NO bioactivity.

Occupational exposure of midwives to nitrous oxide on delivery suites

Aims: To compare environmental and biological monitoring of midwives for nitrous oxide in a delivery suite environment. Methods: Environmental samples were taken over a period of four hours using passive...

A new method for measurement of gas exchange during anaesthesia using an extractable marker gas

A new method for the measurement of pulmonary gas exchange during inhalational anaesthesia is described which measures fresh gas and exhaust gas flows using carbon dioxide as an extractable marker gas. The theoretical precision of the method was compared by Monte Carlo modelling with other approaches which use marker gas dilution. A system was constructed for automated measurement of uptake of oxygen, nitrous oxide, volatile anaesthetic agent and elimination of carbon dioxide by an anaesthetized patient. The accuracy and precision of the method was tested in vitro on a lung gas exchange simulator, by comparison with simultaneous measurements made using nitrogen as marker gas and the Haldane transformation. Good agreement was obtained for measurement of simulated uptake or elimination of all gases studied over a physiologically realistic range of values. Mean bias for oxygen and nitrous oxide uptake was 0.003 l min−1, for isoflurane 0.0001 l min−1 and for carbon dioxide 0.001 l min−1. Limits of agreement lay within 10% of the mean uptake rate for nitrous oxide, within 5% for oxygen and isoflurane and within 1% for carbon dioxide. The extractable marker gas method allows accurate and continuous measurement of gas exchange in an anaesthetic breathing system with any inspired gas mixture.