Significant Amount Of Nitric Oxide Research Articles

NIR Light-Fuse Drug-Free Photothermal Armor-Piercing Microcapsule for Femoral Vein Thrombosis Therapy.

Acute thrombosis and its complications are leading global causes of disability and death. Existing thrombolytic drugs, such as alteplase and urokinase (UK), carry a significant bleeding risk during clinical treatments. Thus, the development of a novel thrombolysis strategy is of utmost urgency. Based on the previous work, the hollow structure of microcapsules (MC) is fabricated. Subsequently, armor-piercing MC, known as Fucoidan/S-Nitrosoglutathione/Melanin@MC (FGM@MC) is obtained, using a layer-by-layer (LBL) self-assembly method. Utilizing near-infrared (NIR) light as a trigger, the FGM@MC demonstrated photothermal thrombolysis at the site of thrombus due to its stable and outstanding photothermal properties. Simultaneously, photothermal stimulation leads to the release of a significant amount of nitric oxide from the FGM@MC, resulting in cavitation effects for mechanical thrombolysis. In vivo experiments confirmed the stable release of nitric oxide under NIR light irradiation. Treatment of femoral vein thrombosis in rats revealed that the thrombolytic effectiveness of FGM@MC+NIR (53.71%) is comparable to that of UK (59.70%). Notably, FGM@MC does not interfere with the coagulation function of rats and exhibits a favorable safety profile. In conclusion, this study demonstrates that the drug-free armor-piercing microcapsule has significant potential in the treatment of thrombosis, offering a safe and effective alternative to traditional thrombolytic therapies.

Polysaccharides from tropical green seaweed Chaetomorpha antennina induces non-specific immune responses and improves antioxidative activities in common carp (Cyprinus carpio) leukocyte culture cell line

Polysaccharides from seaweeds are promising biomolecules that could sustainably improve the health status of cultured fish species. In this study, water-soluble polysaccharides extracted from Chaetomorpha antennina were investigated to determine their physicochemical characteristics and biological activities. C. antennina water-soluble polysaccharides (CAWP) comprised mainly of carbohydrate (69.0 ± 2.3 %), sulphate (12.6 ± 0.5 %), uronic acid (8.8 ± 0.1 %) and protein (3.5 ± 0.2 %). High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD) analysis revealed that CAWP contained mostly arabinose (17.1 ± 2.3 mg/L), galactose (9.3 ± 1.0 mg/L), glucose (5.1 ± 0.6 mg/L), xylose/mannose (1.4 ± 0.6 mg/L) and a small proportion of fucose (0.3 ± 0.1 mg/L). CAWP, with intrinsic viscosity of 0.66 dL/g and estimated molecular weight of 318 kDa, were non-toxic to Carp leukocyte culture (CLC) cell line at concentrations ≤25 μg/mL. CAWP at concentrations of 12.5 and 25 μg/mL stimulated CLC to release significant amount of nitric oxide (NO), reactive oxygen species (ROS) and augmented phagocytic activity. Intracellular antioxidant activities indicated that CAWP did not induce oxidative damage in CLC but could improve superoxide dismutase activity (SOD), total glutathione (tGSH) and decrease malondialdehyde (MDA) level. The findings from our study provide a foundation for the applicability of water-soluble polysaccharides from C. antennina in the aquaculture industry as a potent immunomodulatory agent. • Chaetomorpha antennina is a rich source of sulphated polysaccharides. • Induction of oxidative burst response in Carp leucocytes • Phagocytosis of Red Zymosan® bioparticles by Carp leucocytes • Improved intracellular antioxidant activities

ENDOTHELIAL DYSFUNCTION IN TYPE 2 DIABETES. Review

Relevance. The problem of systematization and refinement of modern concepts of the pathogenesis of endothelial dysfunction (EDF) and its role in the development of microvascular complications of type 2 diabetes mellitus (T2DM) is relevant due to the lack of pathogenetic treatment nowadays, which would include endothelial dysfunction.
 Objective: to conduct an analytical review of the results of scientific research on the mechanisms of EDF in T2DM, with the aim of proposing an integrated modern concept of the pathogenesis of EDF.
 Materials and methods. Review of scientific publications in the international electronic scientific databases of PubMed, Embase and Scopus for keywords for the entire available period (1982-2019).
 Results. The article provides modern data on the modern concept of the pathogenesis of EDF and its role in the development of microvascular complications in T2DM. The pathogenesis of EDF in type 2 diabetes mellitus is based on the following key mechanisms: impaired synthesis of the endothelial fraction of nitric oxide (NO) due to inhibition of the activity of endothelial NO synthase (eNOS); decreased bioavailability of NO because of oxidative stress; activation of the formation of Endothelin-1 (ET1) and expression of endothelin receptors with a predominance of vasoconstriction; inflammation, which is supported by the synthesis of pro-inflammatory cytokines and causes the expression of inducible NO synthase (iNOS), which stimulates the synthesis of a significant amount of NO, which enters into free radical reactions with the formation of cytotoxic products.
 Conclusions. The pathogenesis of endothelial dysfunction is impaired nitric oxide synthesis. Endothelial dysfunction, as an integral mechanism, underlies in the core mechanisms the development of vascular complications in type 2 diabetes.

Hemoglobin as a probe for estimation of nitric oxide emission from plant tissues

BackgroundPlant roots contribute significant amount of nitric oxide (NO) in the rhizosphere as a component of NO in the ecosystem. Various pharmacological investigations on NO research in plants seek to quench endogenous NO by using externally applied NO quenchers, mainly 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) and its more soluble form-carboxy-PTIO (cPTIO). Owing to serious limitations in its application cPTIO is no more a desired compound for such applications.ResultPresent work highlights the significance of using hemoglobin in the bathing solution to not only release endogenous NO from plant tissue but also to quench it in a concentration-dependent manner.ConclusionThe protocol further demonstrates the diffusibility of NO from intracellular locations in presence of externally provided hemoglobin. The proposed method can have widespread applications as a substitute to debatable and currently used cPTIO as a NO scavenger.

Nitric Oxide Measurement from Purified Enzymes and Estimation of Scavenging Activity by Gas Phase Chemiluminescence Method.

In plants, nitrate reductase (NR) is a key enzyme that produces nitric oxide (NO) using nitrite as a substrate. Lower plants such as algae are shown to have nitric oxide synthase enzyme and higher plants contain NOS activity but enzyme responsible for NO production in higher plants is subjected to debate. In plant nitric oxide research, it is very important to measure NO very precisely in order to determine its functional role. A significant amount of NO is being scavenged by various cell components. The net NO production depends in production minus scavenging. Here, we describe methods to measure NO from purified NR and inducible nitric oxide synthase from mouse (iNOS), we also describe a method of measure NO scavenging by tobacco cell suspensions and mitochondria from roots.

Investigation of nitric oxide emission mechanisms in a SI engine fueled with methane/hydrogen blends using a research CFD code

The reaction mechanisms of nitric oxide (NO) emissions are investigated in a spark-ignition (SI) engine fueled with hydrogen/methane blends, for variable equivalence ratio (load variation) and variable hydrogen content. For that purpose, a research three-dimensional computational fluid dynamics code (3D-CFD) is applied, being capable of simulating in high detail the in–cylinder processes. The combustion model of the CFD code includes not only the thermal NO mechanism, widely known as ’Zeldovich mechanism’, but also other alternative NO production mechanisms. Therefore, the NO emission modeling has been enhanced here with the addition of other production paths, such as via the NNH and N2O species formation and the prompt NO mechanism. The NNH path has been shown to be favored at lean and low-temperature combustion conditions especially when hydrogen is present, whereas the N2O path becomes important for lean flames irrespectively of the fuel used. Prompt NO becomes important in stoichiometric and fuel-rich conditions and is also examined here to evaluate its contribution to the NO emissions. Focus is also directed on the local/spatial NO production pattern at each location in the cylinder during the combustion and expansion periods. The calculations are compared with available measurements, in order to quantify the use of these alternative production paths at such conditions and applications. In all cases, the thermal NO mechanism is the dominant production path. On the other hand, with lean flames it has been observed that the N2O path produces significant amount of NO, while the contribution of the NNH mechanism is small, but it is recommended to be also considered in the calculations for increasing the accuracy of the results. The prompt NO is not favored at such conditions, even for the stoichiometric case, and could be even omitted from the combustion model.

Porous, rigid metal(III)-carboxylate metal-organic frameworks for the delivery of nitric oxide

The room temperature sorption properties of the biological gas nitric oxide (NO) have been investigated on the highly porous and rigid iron or chromium carboxylate based metal-organic frameworks Material Institut Lavoisier (MIL)-100(Fe or Cr) and MIL-127(Fe). In all cases, a significant amount of NO is chemisorbed at 298 K with a loading capacity that depends both on the nature of the metal cation, the structure and the presence of additional iron(II) Lewis acid sites. In a second step, the release of NO triggered by wet nitrogen gas has been studied by chemiluminescence and indicates that only a partial release of NO occurs as well as a prolonged delivery at the biological level. Finally, an in situ infrared spectroscopy study confirms not only the coordination of NO over the Lewis acid sites and the stronger binding of NO on the additional iron(II) sites, providing further insights over the partial release of NO only in the presence of water at room temperature.

우리나라 이동오염원의 제어기술의 동향과 발전방안

The major source of harmful air pollutants in Korea have been shifted as economy grows. Particulate matter(PM) and Sulfur dioxide () emitted from industries and coal-fired domestic sectors were important pollutants in 1970`s and later industrializing period of Korea. Then the characteristic of pollution was changed into so-called developed country type pollution. Vehicles have been responsible for significant amount of Nitric oxide () pollution and consequent Ozone formation in urban area since 1990`s. Variety of control measures have been introduced to deal with the vehicle emissions in Seoul Metropolitan Area (SMA). Emission control technologies have successfully reduced pollutants from vehicles. Three-way catalyst for vehicles fueled by gasoline and liquefied petroleum gas (LPG), for example, has achieved large amount of pollutants. Compressed natural gas (CNG) urban bus have penetrated existing diesel bus market and reduces PM and emissions in many Korean cities. However, diesel vehicles are still reaming as a critical emission source of urban area. Diesel vehicles gain more popularity than ever because of their better fuel efficiency and driving power. Unfortunately, it is widely known that the pollutant emissions of diesel vehicles are much larger than those of gasoline and LPG vehicles. In this note, we briefly introduce the trends of emission control strategies which are accomplished by automotive industries for about last ten years. Emission regulation, cleaner fuel, diesel particulate filter (DPF) and other measures are discussed from technical as well as legislative perspectives.

Reexamination of the Direct Electrochemical Reduction of S-Nitrosothiols.

We report here on the electrochemical reduction of S-nitrosothiol species (RSNO). Nitric oxide (NO) is the reported common product from electrochemically reduced RSNOs at physiological pH. However, studies here at pH 7.4 show that during the reduction of RSNOs (-0.6 V to -0.9 V, vs. Ag/AgCl), no significant amount of NO is detected. Gas analysis suggests RSNO are reduced to nitrous oxide (N2O) at pH 7.4 and can only be converted back to NO at more oxidizing voltages. Interestingly, at pH 4.0, a direct one-electron reduction of RSNOs appears to occur and generates significant amounts of NO from RSNO species.

Noise enhances the rapid nitric oxide production by bone cells in response to fluid shear stress

Stochastic resonance is exhibited by many biological systems, where the response to a small stimulus is enhanced with the aid of noise. This intriguing possibility provides a novel paradigm for understanding previously reported osteogenic benefits of low amplitude dynamic loading. However, it is unknown whether bone cell mechanosensitivity is enhanced by noise as an alternative mechanism for an amplified response to small stresses. We studied whether noise of varying intensities enhanced the mechanosensitivity of MC3T3-E1 cells. Nitric oxide (NO) production was measured as the parameter for bone cell activation. Dynamic fluid shear stress stimulated bone cells provided an initial-stress kick was implemented. Without the initial stress-kick bone cells did not release a significant amount of NO demonstrating an essential non-linearity to bone cell responses to stress and the possibility of stochastic resonance in bone cell mechanosensitivity. The rapid NO response of MC3T3-E1 cells to a small periodic fluid shear stress was increased with the addition of noise compared to the response to stress with only noise. This confirms the possibility of stochastic resonance enhancement of NO production by bone cells. Since NO regulate bone formation as well as resorption, our results suggest that noise enhances the activity of bone cells in driving the mechanical adaptation of bone.

Characterization of nitric oxide‐releasing microparticles for the mucosal delivery

For the treatment of female sexual arousal disorder (FSAD), we developed microparticles made of PLGA containing nitric oxide (NO) donor (DETA NONOate) to efficiently deliver NO to vaginal mucosa. The NO-releasing microparticles were prepared by various emulsion methods. SEM and DSC studies were performed to examine the microparticles. The release studies were conducted under various conditions to optimize the loading dose in the microparticles. NO diffusivity through vaginal epithelial cells was evaluated and pharmacological activity of NO-releasing microparticles was examined by assessment of intracellular cGMP level in vaginal cells. Through the modified double emulsion solvent evaporation method (w/o/w(a)), the acid labile DETA NONOate was stabilized during the fabrication process and homogenous morphology and high entrapment efficiency were achieved. DETA NONOate was protected under the acidic conditions of the vagina and NO was released from the microparticles in a controlled manner. A significant amount of NO produced from DETA NONOate penetrated through the vaginal epithelial cells. The intracellular cGMP level increased with the treatment of NO-releasing microparticles in vaginal cells. These findings suggest that NO-releasing microparticles could improve the vaginal blood perfusion and open up the possibilities of novel treatment of FSAD.

Hemorrhagic shock and nitric oxide release from erythrocytic nitric oxide synthase: A quantitative analysis

A large loss of blood during hemorrhage can result in profound shock, a state of hypotension associated with hemodynamic abnormalities. One of the hypotheses to account for this collapse of homeostasis is that the production of nitric oxide (NO), a gas molecule that dilates blood vessels, is significantly impaired during hemorrhage, resulting in a mismatch between O 2 delivery and the metabolic activity in the tissues. NO can be released from multiple sources in the vasculature. Recent studies have shown that erythrocytes express functional endothelial nitric oxide synthase (NOS3), which potentially serves as an intraluminal NO source. NO delivery from this source is complex: erythrocytes are not only NO producers but also act as potent sinks because of the high affinity of NO for hemoglobin. To test our hypothesis that the loss of erythrocytic NOS3 during hemorrhage contributes to NO deficiency-related shock, we have constructed a multicellular computational model that simulates NO production and transport to allow us to quantify the loss of NO under different hemorrhagic conditions. Our model shows that: (1) during mild hemorrhage and subsequent hemodilution (hematocrit > 30%), NO from this intraluminal source is only slightly decreased in the vascular smooth muscle, but the NO level is significantly reduced under severe hemorrhagic conditions (hematocrit < 30%); (2) whether a significant amount of NO from this source can be delivered to vascular smooth muscle is strongly dependent on the existence of a protective mechanism for NO delivery; (3) if the expression level of NOS3 on erythrocytes is similar to that on endothelial cells, we estimate ∼ 13 pM NO at the vascular smooth muscle from this source when such a protective mechanism is involved. This study provides a basis for detailed studies to characterize the impairment of NO release pathways during hemorrhage and yield important insights for the development of resuscitation methods.

Resemblance in gas composition of Ar–N2–O2 plasmas and Ar–NO plasmas

We measured the steady-state gas composition of plasmas produced from Ar–N2–O2 mixtures and Ar–NO mixtures with quantitative mass spectrometry. In the former, mainly N2 and O2, but also a significant amount of nitric oxide (NO) was formed, i.e. up to 5% of the background gas was NO. In the inverse experiment, in which NO was admixed to an argon plasma, up to 92% of the NO was converted into N2 and O2. The observed molecules are mostly generated in wall association processes but also by gas phase reactions between N atoms and O2 molecules leading to NO. The two types of plasmas show a strong mutual resemblance in the steady-state gas composition if substantial dissociation can be reached in the residence time of the gases in the plasma, i.e. ≈5% NO and ≈95% N2 and O2, although the starting conditions are completely different. It seems that in first order the system prefers to produce the most thermodynamically stable molecules.

Inhibition of reactive oxygen species attenuates aneurysm formation in a murine model

Reactive oxygen species (ROS) are increased in human abdominal aortic aneurysms (AAA). NADPH oxidases are the predominant source of superoxide anion (O 2 −) in the vasculature. Inducible nitric oxide synthase (iNOS) produces a significant amount of nitric oxide (NO) during inflammatory processes. We hypothesized that ROS produced by NADPH oxidases and iNOS played an important role in aneurysm formation. We examined this hypothesis using selective blockade of NADPH oxidases and iNOS in a murine model of AAA. Mice, including C57BL/6, iNOS knockout (iNOS −/−) mice, and its background matched control (C57BL/6), underwent AAA induction by periaortic application of CaCl 2. Aortic diameter was measured at aneurysm induction and harvest. Beginning 1 week prior to aneurysm induction and continuing to aortic harvest 6 weeks later, one group of the C57BL/6 mice were treated with orally administered apocynin (NADPH oxidase inhibitor). Control mice were given water. The mean diameter and change in diameter of each group were compared with concurrent controls. Aortic levels of the NO metabolite, NO x (NO 2 and NO 3), were significantly increased in CaCl 2-treated wild type mice. INOS −/− mice were partly resistant to aneurysm induction. This was associated with reduced expression of matrix metalloproteinase (MMP)-2 and MMP-9 and decreased production of NO x in the aortic tissues. Inhibition of NADPH oxidase by apocynin also blocked aneurysm formation. In conclusion, both iNOS deficiency and NADPH oxidase inhibition suppressed aneurysm formation in association with decreased NO x levels. These studies suggest that both NADPH oxidase and iNOS pathways contribute to ROS production and AAA development.

Nitric oxide release from nitric oxide synthase on erythrocytes during hemorrhagic shock

A large loss of blood during hemorrhage could result in profound shock, a state of hypotension associated with hemodynamic abnormalities. One of the hypotheses for the hemorrhage‐induced collapse of homeostasis is that the production of nitric oxide (NO), a gas molecule that dilates blood vessels to match O2 delivery to the metabolic activity of local tissue, is significantly impaired because of the reduced blood volume and flow. Recent studies show that erythrocytes express functional endothelial nitric oxide synthase (NOS3), which potentially serves as an intraluminal NO source. We hypothesized that the loss of NOS3 on erythrocytes during hemorrhage contributes to the NO‐deficiency related shock. In this study, we constructed a multi‐cellular computational model that simulates NO production from NOS3 on erythrocytes and its transport around an arteriole. Our simulations show that whether a significant amount of NO from this source can be delivered to vascular smooth muscle is strongly dependent on the existence of a protected mechanism for NO delivery. Our result also predicts that NO delivery from erythrocytes decreases with blood loss during hemorrhage; with a critically low hematocrit (8%), ∼50% of the NO bioactivity from NOS3 on erythrocytes delivered to smooth muscle is lost, compared with the condition of 45% hematocrit. (Supported by NIH grants HL79087 and HL18292).

Nitrite protonation as a necessary stage in the generation of nitric oxide from nitrite in biological systems

The yields of nitric oxide from 1 mM and 10 mM sodium dithionite in 5 or 150 mM solutions of HEPES buffer (pH 7.4) differed by a factor of 200. Dithionite acted as both a strong reducing agent and an agent responsible for local acidification of the solutions without significant changes in pH. The concentration of nitric oxide was estimated by electron paramagnetic resonance (EPR) by monitoring its incorporation into water-soluble complexes of Fe with N-methyl-D-glucamine dithiocarbamate (MGD), which resulted in the formation of EPR-detectable mononitrosyl complexes of iron. Ten seconds after dithionite addition, the concentration of mononitrosyl iron complexes reached 2 μM, whereas it did not become greater than 0.01 μM in 5 mM HEPES buffer. It has been suggested that this difference results from a longer lifetime of a localized decrease in pH in a weaker buffer solution. This time could be long enough for the protonation of some nitrite molecules. Nitrous acid thus formed decomposed to nitric oxide. A difference in nitric oxide formation from nitrite in weak and strong buffer solutions was also observed in the presence of hemoglobin (0.3 mM) or serum albumin (0.5 mM). However, in the weak buffer the nitric oxide yield was only three-four times greater than in the strong buffer. An increase in the nitric oxide yield from nitrite was observed in solutions containing both proteins. A significant amount of nitric oxide from nitrite was formed in mouse liver preparation subjected to freezing and thawing procedure followed by slurrying in 150 mM HEPES buffer (pH 7.4) and dithionite addition (10 mM). We suggest that the presence of zones with lowered pH values in cells and tissues may be responsible for the predominance of the acidic mechanism of nitric oxide formation from nitrite. The contribution of nitric oxide formation from nitrite catalyzed by heme-containing proteins as nitrite reductases may be minor under these conditions.

In vitro induction of nitric oxide by mouse peritoneal macrophages treated with human placental extract

Nitric oxide (NO) is an important cellular mediator of tissue repair. It is produced in macrophages by the enzyme inducible nitric oxide synthase ( iNOS) during wound healing. An aqueous extract of human placenta used as wound healer, has been investigated in terms of induction of NO by mouse peritoneal macrophages as well as human monocyte derived macrophages. NO production was estimated in macrophages culture supernatants. Incubation of 0.1 to 20 mg/ml of placental extract with 2 × 10 6 cells in vitro produced 10 to 100 μM of nitrite ( n = 4) in a dose dependent manner suggesting production of NO. With increase of NO production, NADPH present in the applied extract decreased proportionately. Application of L-N G monomethyl arginine ( L-NMMA), an NO synthase (NOS) inhibitor, reduced the production of NO at the basal level. Dose dependent release of IFN-γ with respect to placental extract by the mouse macrophages was observed. It has been observed that human monocytes derived macrophages also produced significant amount of NO by induction of the extract. Similar induction of NO by placental extract in presence and absence of polymyxin B suggested that this property is not likely to be mediated by the endotoxin/LPS.

Significant contamination of superoxide dismutases and catalases with lipopolysaccharide-like substances

Commercially available superoxide dismutase (SOD) and catalase induced remarkable morphological changes in cultured peritoneal resident macrophages (PRMs). The morphology resembled that of cells stimulated with various macrophage-activating substances such as bacterial lipopolysaccharides (LPS). PRMs treated with SOD and catalase for 24 h produced a significant amount of nitric oxide. Peritoneal thioglycollate-exudated macrophages (PEMs) that were induced to die by combined treatment with LPS and cycloheximide (protein synthesis inhibitor) were killed by the treatment with SOD and catalase in the presence of cycloheximide. The effect of SOD and catalase was heat-resistant and was not found in PEMs of the C3H/HeJ mouse, an LPS low responder strain. These results strongly indicated the presence of LPS-like substances in the sample of SOD and catalase used. An examination of commercially available SOD and catalase samples for the presence of LPS-like substances demonstrated that many were contaminated. The LPS contamination was directly confirmed by bacterial endotixins test. It is quite important to take into consideration that commercially available SODs and catalases may be contaminated with LPS and the contaminants may affect the results of studies.

Basal nitric oxide production contributes to membrane potential and vasotone regulation of guinea pig in vitro spiral modiolar artery

Nitric oxide (NO) is a potent vasodilating agent implicated in cochlear blood flow regulation. We recently demonstrated that exogenously applied NO donor DPTA-NONOate hyperpolarizes both endothelial and smooth muscle cells of in vitro spiral modiolar artery (SMA) via activation of ATP-sensitive K + channels (K ATP). Also, NO was detected in the SMA cells by NO indicator dye in the in vitro basal condition. Using intracellular recording techniques, electrochemical NO-sensing measurement, and a vaso-diameter video tracking method, we investigated the basal release of NO from the in vitro SMA and its role in the vascular function. We found that (1) 300 μM L-NAME, a NO synthase inhibitor, and 3 μM glipizide caused a depolarization of ∼4.5 and ∼3.2 mV, respectively, in cells with a resting potential less negative than −60 mV; (2) NO sensor in the close vicinity of the SMA detected a NO concentration of ∼50 nM that was suppressed by L-NAME and enhanced by L-arginine (1–1000 μM); (3) NO donor DPTA-NONOate (0.1–30 μM) applications produced about 8–245 nM of NO in the recording bath. These data indicate a NO concentration–hyperpolarization relation, with an EC 50 of 22 nM. (4) Finally, L-NAME but not glipizide produced a 4.8% reduction in SMA diameter (∼50 μm) in the majority of SMAs, whereas NONOate (10 μM) always caused a dilation. Both the induced constriction and dilation were not significantly affected by 3 μM glipizide. We conclude that a significant amount of NO (>50 nM) is tonically released from the in vitro SMA, which is above the EC 50 for activation of K ATP, and thus contributes to the membrane polarization. The basal release of NO also contributes to vasotone relaxation, but the K ATP activation appears to play little role in the relaxation of the in vitro SMA.

A theoretical model of nitric oxide transport in arterioles: frequency- vs. amplitude-dependent control of cGMP formation.

Nitric oxide (NO) plays many important physiological roles, including the regulation of vascular smooth muscle tone. In response to hemodynamic or agonist stimuli, endothelial cells produce NO, which can diffuse to smooth muscle where it activates soluble guanylate cyclase (sGC), leading to cGMP formation and smooth muscle relaxation. The close proximity of red blood cells suggests, however, that a significant amount of NO released will be scavenged by blood, and thus the issue of bioavailability of endothelium-derived NO to smooth muscle has been investigated experimentally and theoretically. We formulated a mathematical model for NO transport in an arteriole to test the hypothesis that transient, burst-like NO production can facilitate efficient NO delivery to smooth muscle and reduce NO scavenging by blood. The model simulations predict that 1) the endothelium can maintain a physiologically significant amount of NO in smooth muscle despite the presence of NO scavengers such as hemoglobin and myoglobin; 2) under certain conditions, transient NO release presents a more efficient way for activating sGC and it can increase cGMP formation severalfold; and 3) frequency-rather than amplitude-dependent control of cGMP formation is possible. This suggests that it is the frequency of NO bursts and perhaps the frequency of Ca(2+) oscillations in endothelial cells that may limit cGMP formation and regulate vascular tone. The proposed hypothesis suggests a new functional role for Ca(2+) oscillations in endothelial cells. Further experimentation is needed to test whether and under what conditions in silico predictions occur in vivo.