Stimulatory Effect Of Nitric Oxide Research Articles

Evaluation of the pharmacological involvement of ATP-sensitive potassium (KATP) channels in the antidepressant-like effects of topiramate on mice.

Acute doses of topiramate (TPM) have been shown to reduce immobility time in the mice forced swimming test (FST) through inhibition of the nitric oxide (NO) pathway. Adenosine triphosphate-sensitive potassium (KATP) channels are known to have an active role in depression. This study investigates the potential participation of KATP channels in the antidepressant-like effect of TPM through the stimulatory effects of NO. FST and tail suspension tests (TST) were applied to adult male mice for assessment of the antidepressant-like activity of TPM. Different doses of glibenclamide and cromakalim were also applied in order to investigate the involvement of KATP channels. Fluoxetine was used as a positive control for evaluation of antidepressant-like effects. In addition, each animal's locomotor activity was evaluated by the open-field test (OFT). TPM (30mg/kg intraperitoneal (i.p.)) had a significant reductive effect on the immobility behavior similar to fluoxetine (20mg/kg). Co-administration of sub-effective doses of glibenclamide (1mg/kg i.p.) and TPM (10mg/kg i.p.) led to significant synergistic effects in FST and TST. Additionally, the results showed that administration of the sub-effective dose of cromakalim (0.1 and 0.3mg/kg i.p.) blocked the antidepressant-like effects of TPM (30mg/kg i.p.) in both tests. These interventions had no impact on the locomotor movement of mice in OFT. This study shows that the antidepressant-like activity of TPM may potentially be mediated by the blocking of the KATP channels.

L-Arginine Enhances Protein Synthesis by Phosphorylating mTOR (Thr 2446) in a Nitric Oxide-Dependent Manner in C2C12 Cells.

Muscle atrophy may arise from many factors such as inactivity, malnutrition, and inflammation. In the present study, we investigated the stimulatory effect of nitric oxide (NO) on muscle protein synthesis. Primarily, C2C12 cells were supplied with extra L-arginine (L-Arg) in the culture media. L-Arg supplementation increased the activity of inducible nitric oxide synthase (iNOS), the rate of protein synthesis, and the phosphorylation of mTOR (Thr 2446) and p70S6K (Thr 389). L-NAME, an NOS inhibitor, decreased NO concentrations within cells and abolished the stimulatory effect of L-Arg on protein synthesis and the phosphorylation of mTOR and p70S6K. In contrast, SNP (sodium nitroprusside), an NO donor, increased NO concentrations, enhanced protein synthesis, and upregulated mTOR and p70S6K phosphorylation, regardless of L-NAME treatment. Blocking mTOR with rapamycin abolished the stimulatory effect of both L-Arg and SNP on protein synthesis and p70S6K phosphorylation. These results indicate that L-Arg stimulates protein synthesis via the activation of the mTOR (Thr 2446)/p70S6K signaling pathway in an NO-dependent manner.

Interplay between nitric oxide, ethylene, and gibberellic acid regulating the release of Amaranthus retroflexus seed dormancy

A very small percentage, below 10%, of Amaranthus retroflexus seeds were germinated at 25 °C in the light and thus the seeds were considered to be primary dormant. Nitric oxide (NO) applied for only 5 h stimulated germination of these non-deep physiologically dormant seeds. Likewise, ethephon, ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and gibberellic acid (GA3) induced dormancy release. The stimulatory effect of NO, ACC, and GA3 on germination was associated with increased ethylene production prior to radicle protrusion. The nitric oxide scavenger, cPTIO, antagonized the stimulatory effect of GA3, ethephon, and ACC on seed germination, indicating that the presence of endogenous NO is required for dormancy release by these compounds. This scavenger inhibited both germination and ethylene production stimulated by NO and GA3. An inhibitor of ethylene binding to its receptor, 2,5-norbornadiene (NBD), antagonized the beneficial effect of ethylene and NO, indicating that ethylene action is necessary for the appearance of seed response to these gases. The ACC synthase inhibitor, aminoethoxyvinylglycine (AVG), and the ACC oxidase inhibitor, α-amino-isobutyric acid (AIB), strengthened the effect of NBD on the germination of NO-pretreated seeds. Induction of germination of dormant seeds by NO, ethephon or GA3 was associated with initiation of the cell cycle prior to radicle protrusion. The data presented indicate NO crosstalk with ethylene and GA3 in regulating dormancy release in A. retroflexus seeds.

Effects of Nitric Oxide on Renal Proximal Tubular Na+ Transport.

Nitric oxide (NO) has a wide variety of physiological functions in the kidney. Besides the regulatory effects in intrarenal haemodynamics and glomerular microcirculation, in vivo studies reported the diuretic and natriuretic effects of NO. However, opposite results showing the stimulatory effect of NO on Na+ reabsorption in the proximal tubule led to an intense debate on its physiological roles. Animal studies have showed the biphasic effect of angiotensin II (Ang II) and the overall inhibitory effect of NO on the activity of proximal tubular Na+ transporters, the apical Na+/H+ exchanger isoform 3, basolateral Na+/K+ ATPase, and the Na+/HCO3− cotransporter. However, whether these effects could be reproduced in humans remained unclear. Notably, our recent functional analysis of isolated proximal tubules demonstrated that Ang II dose-dependently stimulated human proximal tubular Na+ transport through the NO/guanosine 3′,5′-cyclic monophosphate (cGMP) pathway, confirming the human-specific regulation of proximal tubular transport via NO and Ang II. Of particular importance for this newly identified pathway is its possibility of being a human-specific therapeutic target for hypertension. In this review, we focus on NO-mediated regulation of proximal tubular Na+ transport, with emphasis on the interaction with individual Na+ transporters and the crosstalk with Ang II signalling.

Immunomodulatory Potential of the Polysaccharide-Rich Extract from Edible Cyanobacterium Nostoc commune

A dry sample of Nostoc commune from an organic farm in Pingtung city (Taiwan) was used to prepare polysaccharide-rich (NCPS) extract. The conditioned medium (CM) from NCPS-treated human peripheral blood (PB)-mononuclear cells (MNC) effectively inhibited the growth of human leukemic U937 cells and triggered differentiation of U937 monoblast cells into monocytic/macrophagic lines. Cytokine levels in MNC-CMs showed upregulation of granulocyte/macrophage-colony stimulatory factor and IL-1β and downregulation of IL-6 and IL-17 upon treatment with NCPS. Moreover, murine macrophage RAW264.7 cells treated with NCPS exhibited the stimulatory effects of nitric oxide and superoxide secretion, indicating that NCPS might activate the immunity of macrophages. Collectively, the present study demonstrates that NCPS from N. commune could be potentially used for macrophage activation and consequently inhibited the leukemic cell growth and induced monocytic/macrophagic differentiation.

Time-dependent inhibitory effects of cGMP-analogues on thrombin-induced platelet-derived microparticles formation, platelet aggregation, and P-selectin expression

In platelets, nitric oxide (NO) activates cGMP/PKG signalling, whereas prostaglandins and adenosine signal through cAMP/PKA. Cyclic nucleotide signalling has been considered to play an inhibitory role in platelets. However, an early stimulatory effect of NO and cGMP-PKG signalling in low dose agonist-induced platelet activation have recently been suggested. Here, we investigated whether different experimental conditions could explain some of the discrepancy reported for platelet cGMP-PKG-signalling. We treated gel-filtered human platelets with cGMP and cAMP analogues, and used flow cytometric assays to detect low dose thrombin-induced formation of small platelet aggregates, single platelet disappearance (SPD), platelet-derived microparticles (PMP) and thrombin receptor agonist peptide (TRAP)-induced P-selectin expression. All four agonist-induced platelet activation phases were blocked when platelets were costimulated with the PKG activators 8-Br-PET-cGMP or 8-pCPT-cGMP and low-doses of thrombin or TRAP. However, extended incubation with 8-Br-PET-cGMP decreased its inhibition of TRAP-induced P-selectin expression in a time-dependent manner. This effect did not involve desensitisation of PKG or PKA activity, measured as site-specific VASP phosphorylation. Moreover, PKG activators in combination with the PKA activator Sp-5,6-DCL-cBIMPS revealed additive inhibitory effect on TRAP-induced P-selectin expression. Taken together, we found no evidence for a stimulatory role of cGMP/PKG in platelets activation and conclude rather that cGMP/PKG signalling has an important inhibitory function in human platelet activation.

Stimulatory and period-specific effect of nitric oxide on in vitro caulogenesis in Albizzia lebbeck (L.) Benth.

The paper reports stimulatory effect of nitric oxide (NO) on in vitro caulogenesis in Albizzialebbeck, a tree legume. Exogenously supplied NO donor, sodium nitroprusside (SNP) stimulated shoot differentiation from hypocotyl explants of Albizzia lebbeck, excised from its in vitro seedlings. Potassium ferrocyanide, a structural analog of SNP incapable of releasing NO, did not promote shoot organogenesis. Likewise, metabolic products of NO, NO2− and NO3−, provided as NaNO2 and NaNO3 did not enhance shoot differentiation. The NO scavenger, 2-(4-carboxy-phenyl)-4, 4, 5, 5-tetramethylimideazoline-1-oxyl-3-oxide (cPTIO), supplemented along with SNP, at equimolar concentration, reversed the stimulatory effect of the latter, thus, confirming the role of NO in promotion of in vitro caulogenesis. The transfer of explants cultured on the basal medium (BM) to the same containing SNP and vice versa after different time intervals revealed that for its enhancing effect, SNP was required only during the initial phase (5 days) of culture. Its presence or administration beyond 5 days neither promoted nor inhibited the caulogenic response.

Signaling-mediated Functional Activation of Inducible Nitric-oxide Synthase and Its Role in Stimulating Platelet Activation

Nitric oxide (NO) is a short lived secondary messenger, synthesized by nitric-oxide synthases (NOS). It is believed that the activity of inducible NOS (iNOS) is regulated primarily at the transcription level by inducing expression of iNOS mRNA and protein, which then continuously produces NO, until its degradation. Platelets do not have the nuclear transcriptional regulatory mechanisms of the iNOS gene and are believed to generate NO in response to agonist stimulation via endothelial NOS (eNOS). However, here we show that agonist-induced NO production is only partially eNOS-dependent and is also mediated by iNOS. Platelet agonist-induced NO production is significantly reduced in iNOS-knockout platelets. Platelet NO production occurs within seconds after agonist addition and is not accompanied by changes in iNOS protein levels, indicating a signaling-mediated functional activation mechanism of iNOS. Importantly, iNOS knock-out and iNOS inhibitors reduce agonist-induced platelet secretion and aggregation and cGMP levels, indicating that iNOS activation is important in stimulating platelets via the newly identified NO-cGMP-dependent platelet secretion pathway. Furthermore, iNOS knock-out mice have prolonged bleeding time, suggesting that this novel mode of regulation of iNOS activity plays a physiologically relevant role in hemostasis.

Involvement of Protein Kinase A in Nitric Oxide Stimulating Effect on a BKCa Channel of Human Dermal Fibroblasts

We reported previously that a large-conductance Ca2+-activated K+ (BK(Ca)) channel constitutes a significant fraction of the K+ current in human dermal fibroblasts, and that nitric oxide (NO) increases the open-channel probability (NPo) of BK(Ca) channels via a soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) pathway. The purpose of this study was to investigate whether the adenylate cyclase (AC)/cAMP/protein kinase A (PKA) pathway may also be involved in NO action on BK(Ca) channels in human dermal fibroblasts. Electrophysiological single-channel recordings were performed on fifth-passage cells of human penile skin cultures. KT5720 (specific PKA inhibitor) blocked the stimulatory effect of sodium nitroprusside (NO donor) on BK(Ca) channels. By contrast, forskolin (AC activator) or 8-bromo-cAMP (cell-permeable cAMP analog) did not increase the NPo of the channel. The PKA catalytic subunit (PKAcs) alone did not increase the NPo of the channel in cell-attached and inside-out patches, however, PKAcs with cGMP increased the NPo. In contrast, PKAcs with cGMP did not increase the NPo of BK(Ca) channels with 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one pretreatment, and KT5720 pretreatment also blocked the stimulatory effect of 8-Br-cGMP. In conclusion, the present data suggest the involvement of PKA in the stimulatory effect of NO on the BK(Ca) channel in human dermal fibroblasts through cGMP.

Nitric Oxide Destabilizes Pias3 and Regulates Sumoylation

Small ubiquitin-related protein modifiers (SUMO) modification is an important mechanism for posttranslational regulation of protein function. However, it is largely unknown how the sumoylation pathway is regulated. Here, we report that nitric oxide (NO) causes global hyposumoylation in mammalian cells. Both SUMO E2 conjugating enzyme Ubc9 and E3 ligase protein inhibitor of activated STAT3 (Pias3) were targets for S-nitrosation. S-nitrosation did not interfere with the SUMO conjugating activity of Ubc9, but promoted Pias3 degradation by facilitating its interaction with tripartite motif-containing 32 (Trim32), a ubiquitin E3 ligase. On the one hand, NO promoted Trim32-mediated Pias3 ubiquitination. On the other hand, NO enhanced the stimulatory effect of Pias3 on Trim32 autoubiquitination. The residue Cys459 of Pias3 was identified as a target site for S-nitrosation. Mutation of Cys459 abolished the stimulatory effect of NO on the Pias3-Trim32 interaction, indicating a requirement of S-nitrosation at Cys459 for positive regulation of the Pias3-Trim32 interplay. This study reveals a novel crosstalk between S-nitrosation, ubiquitination, and sumoylation, which may be crucial for NO-related physiological and pathological processes.

Possible Link Between NO Concentrations and COX‐2 Expression in Systems Treated with Soy‐Isoflavones

The production of nitric oxide (NO) emerges as an essential determinant in auto- and paracrine signaling. NO is known to be generated under inflammatory conditions, carcinogenesis, and circulatory shock. The large amount of NO produced in response to cytokines plays an important role in inflammatory conditions. Cyclooxygenase (COX), the central enzyme in prostanoid biosynthesis, is involved in the first step of prostanoid synthesis from arachidonic acid. The reported studies to evaluate the relationship between NO and COX-2 have revealed both inhibitory and stimulatory effects of NO on COX-2 expression. Genistein, one of soy-isoflavones, is a polyphenolic flavonoid and a potent antioxidant and anti-inflammatory agent. In the present article, the effect of soy-isoflavones on NO production and COX-2 gene expression was examined. NO production by soy-isoflavones was greatly increased even though eNOS and iNOS expression were not different from nontreated control. The increment of NO was accompanied with the elevated expression of COX-2 and the concentrations of PGE2. The COX-2 stimulatory effect of soy-isoflavones appeared to be modulated by ERK-1 and -2 and p38. In mammalian cancer system, incubation with the NO donor sodium nitroprusside (SNP) resulted in a slight upregulation of COX-2, and cotreatment with genistein decreased COX-2 expression possibly by the activation of AMP-activated protein kinase (AMPK).

Nitric Oxide Promotes Airway Epithelial Wound Repair through Enhanced Activation of MMP-9

The airway epithelium provides a protective barrier against inhaled environmental toxins and microorganisms, and epithelial injury initiates a number of processes to restore its barrier integrity, including activation of matrix metalloproteinases such as MMP-9 (92-kD gelatinase B). Airway epithelial cells continuously produce nitric oxide (NO), which has been linked to cell migration and MMP-9 regulation in several cell types, but the importance of epithelial NO in mediating airway epithelial repair or MMP-9 activation is unknown. Using primary or immortalized human bronchial epithelial cells, we demonstrate that low concentrations of NO promote epithelial cell migration and wound repair in an in vitro wound assay, which was associated with increased localized expression and activation of MMP-9. In addition, in HBE1 cells that were stably transfected with inducible NOS (NOS2), to mimic constitutive epithelial NOS2 expression in vivo, NOS inhibition decreased epithelial wound repair and MMP-9 expression. The stimulatory effects of NO on epithelial wound repair and MMP-9 expression were dependent on cGMP-mediated pathways and were inhibited by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase. Inhibition of cGMP-dependent protein kinase (PKG) attenuated NO-mediated epithelial wound closure, but did not affect MMP-9 expression. However, pharmacologic MMP inhibition and siRNA knockdown of MMP-9 expression demonstrated the contribution of MMP-9 to NO-mediated wound closure. Overall, our results demonstrate that NOS2-derived NO contributes to airway epithelial repair by both PKG-dependent and -independent mechanisms, and involves NO-dependent expression and activation of MMP-9.

Regulation of FoxO1 Transcription Factor by Nitric Oxide and Cyclic GMP in Cultured Rat Granulosa Cells

FoxO1 is a transcription factor implicated in a multitude of physiological processes including cell cycle progression, apoptosis and insulin signaling. Recent findings indicate that FoxO1 is a key regulator during the proliferation and maturation of granulosa cells. Over the past several years, it has become evident that nitric oxide (NO) and cGMP modulate ovarian function. There has been no information, however, about whether NO-cGMP affects FoxO1 expression or about the relationship between NO-cGMP and FoxO1. In the present study, we used immunoblot analysis to determine whether NO and cGMP affect FoxO1 expression in cultured granulosa cells. Our results clearly showed that FSH suppressed FoxO1 expression in a time-dependent manner, and that NO-cGMP stimulated FoxO1 expression in cultured granulosa cells. In addition, this stimulatory effects of NO and cGMP can be blocked by FSH in cultured granulosa cells. These findings demonstrate that NO and cGMP influence FoxO1 expression possibly through antagonizing the action of FSH in cultured granulosa cells. Results of both immunoblot analysis and immunohistochemistry also show that estradiol implantation do not affect the expression of FoxO1 in rat granulosa cells as gonadotrophins do, indicating that mechanism of estradiol on granulosa cells is different from gonadotrophins. Together, our experiments suggest that expression of FoxO1 in rat granulosa cells can be regulated by gonadotrophins and the NO/cGMP signaling pathway.

Effect of nitric oxide on hyperpolarization-activated current in substantia gelatinosa neurons of rats

Central sensitization is the hyperexcitability of spinal processing after peripheral nerve injury or inflammation. This phenomenon may be associated with nitric oxide (NO) signal pathway in synapse. Here, we have investigated the effect of NO on hyperpolarization-activated inward current ( I h) in substantia gelatinosa (SG) neurons, using the whole-cell patch clamp technique. I h was increased by the application of sodium nitro prusside (SNP, a NO donor) or 8Br-cGMP. The stimulatory effects of NO were abolished by guanylyl cyclase inhibitor, ODQ, suggesting that the effect of NO was mediated by cGMP. However, this effect of NO was not prevented by the pretreatment with KT5823, PKG inhibitor. Taken together, the activation of I h in SG neurons could be mediated by NO-cGMP dependent pathway. These results reveal an involvement of NO in excitability of SG neuron via the activation of I h may be associated with central sensitization.

A role for nitric oxide in sensory‐induced neurogenesis in an adult insect brain

In the adult cricket, neurogenesis occurs in the mushroom bodies, the main integrative structures of the insect brain. Mushroom body neuroblast proliferation is modulated in response to environmental stimuli. However, the mechanisms underlying these effects remain unspecified. In the present study, we demonstrate that electrical stimulation of the antennal nerve mimics the effects of olfactory activation and increases mushroom body neurogenesis. The putative role of nitric oxide (NO) in this activity-regulated neurogenesis was then explored. In vivo and in vitro experiments demonstrate that NO synthase inhibition decreases, and NO donor application stimulates neuroblast proliferation. NADPH-d activity, anti-L-citrulline immunoreactivity, as well as in situ hybridization with a probe specific for Acheta NO synthase were used to localize NO-producing cells. Combining these three approaches we clearly establish that mushroom body interneurons synthesize NO. Furthermore, we demonstrate that experimental interventions known to upregulate neuroblast proliferation modulate NO production: rearing crickets in an enriched sensory environment induces an upregulation of Acheta NO synthase mRNA, and unilateral electrical stimulation of the antennal nerve results in increased L-citrulline immunoreactivity in the corresponding mushroom body. The present study demonstrates that neural activity modulates progenitor cell proliferation and regulates NO production in brain structures where neurogenesis occurs in the adult insect. Our results also demonstrate the stimulatory effect of NO on mushroom body neuroblast proliferation. Altogether, these data strongly suggest a key role for NO in environmentally induced neurogenesis.

Activation of NF-κB by nitric oxide/cGMP in human blood CD14+ cells

Nuclear factor κB (NF-κB) is a common transcription factor regulating expression of multiple genes relevant for immune reactions. It may by activated by numerous stimuli and a number of data have indicated a relationship between its activity and intracellular concentration of cGMP. Increased levels of the nucleotide have been shown to affect expression of TNFα, IL-1, IL-6 and NOS2 in various immune cells. Particularly, cGMP has been shown to affect several important functions of cells belonging to a monocyte/macrophage lineage. Recently, we reported that in freshly isolated human peripheral blood mononuclear cells (PBMC) the NF-κB activity was modulated through a cGMP-dependent pathway. The aim of this study was to determine whether and how cGMP may affect an activity of NF-κB in human CD14 monocytes. They express soluble guanylyl cyclase (sGC) as well as cGMP-dependent protein kinase I (PKG I). We show that in this cells nitric oxide (NO) stimulates the NF-κB activity at low and inhibits it at high doses. This effect is mimicked by membrane-permeable analogues of cGMP. Using specific inhibitors, we also show that stimulatory effect of NO/cGMP on the NF-κB activity is mediated by PKG I. This observation is additionally supported by the fact that stimulatory effect of NO disappears in cultured cells lacking PKG I. Therefore, our results show that at least some reported effects of NO/cGMP on monocytic cells directly involve PKG I and NF-κB.

Interaction of selective amino acid residues of K(ca) channels with carbon monoxide.

The activation of big-conductance K(Ca) channels in vascular smooth muscle cells by carbon monoxide (CO) has been demonstrated previously. One specific target of CO on K(Ca) channel proteins is the histidine residue. The roles of other amino acid residues on the functionality of K(Ca) channels, as well as their reactions to CO, have been unclear. In the present study, the cell-free single channel recording technique was used to investigate the chemical modification of K(Ca) channels by CO and other chemical agents. The modification of negatively charged carboxyl groups and the epsilon -amino group of lysine did not affect the open probability, but decreased single-channel conductance of K(Ca) channels. When sulfhydryl groups of cysteine were modified with N-ethylmaleimide, the open probability of K(Ca) channels was decreased, but single-channel conductance was not affected. None of the above chemical modifications affected the CO-induced increase in the open probability of K(Ca) channels. However, N-ethylmaleimide treatment reduced the stimulatory effect of nitric oxide (NO) on K(Ca) channels. Finally, pretreatment of smooth muscle cells with NO abolished the effects of subsequently applied CO on K(Ca) channel proteins. Our study demonstrates that CO and NO acted on different amino acid residues of K(Ca) channel proteins. The interaction of CO and NO determines the functional status of K(Ca) channels in vascular smooth muscle cells

Dual effect of nitric oxide on cytosolic Ca2+ concentration and insulin secretion in rat pancreatic beta-cells.

In isolated rat pancreatic beta-cells, the nitric oxide (NO) donor NOC-7 at 1 microM reduced the amplitude of the oscillations of cytosolic Ca(2+) concentration ([Ca(2+)](c)) induced by 11.1 mM glucose, and at 10 microM terminated them. In the presence of N(G)-nitro-l-arginine (l-NNA), however, NOC-7 at 0.5 and 1 microM increased the amplitude of the [Ca(2+)](c) oscillations, although the NO donor at 10 microM still suppressed them. Aqueous NO solution also had a dual effect on the [Ca(2+)](c) oscillations. The soluble guanylate cyclase inhibitor LY-83583 and the cGMP-dependent protein kinase inhibitor KT5823 inhibited the stimulatory effect of NO, and 8-bromo-cGMP increased the amplitude of the [Ca(2+)](c) oscillations. Patch-clamp analyses in the perforated configuration showed that 8-bromo-cGMP inhibited whole cell ATP-sensitive K(+) currents in the isolated rat pancreatic beta-cells, suggesting that the inhibition by cGMP of ATP-sensitive K(+) channels is, at least in part, responsible for the stimulatory effect of NO on the [Ca(2+)](c) oscillations. In the presence of l-NNA, the glucose-induced insulin secretion from isolated islets was facilitated by 0.5 microM NOC-7, whereas it was suppressed by 10 microM NOC-7. These results suggest that NO facilitates glucose-induced [Ca(2+)](c) oscillations of beta-cells and insulin secretion at low concentrations, which effects are mediated by cGMP, whereas NO inhibits them in a cGMP-independent manner at high concentrations.

Stimulatory effects of nitric oxide donors on histamine release in isolated rat gastric mucosal cells.

We previously reported stimulatory effects of endogenous and exogenous nitric oxide (NO) on gastric acid secretion. In the present study, we investigated effects of NO donors on release of histamine, which is related to acid secretion, in isolated rat gastric mucosal cells. NO donors such as (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexanamide (NOR 1) and sodium nitroprusside significantly augmented the histamine release. It was inhibited by 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-amide (carboxy-PTIO), a NO scavenger, and 6-(phenylamino)-5,8-quinolinedione (LY83583), a soluble guanylate cyclase inhibitor. Dibutyryl cyclic GMP also stimulated histamine release. These results suggest that NO donors act on cyclic GMP pathway in isolated gastric mucosal cells, resulting in facilitation of histamine release. NO may stimulate gastric acid secretion through histamine release from the histamine-containing cells, possibly enterochromaffin-like cells.

Chitosan increases the release of renal dipeptidase from porcine renal proximal tubule cells

Renal dipeptidase (RDPase, membrane dipeptidase, dehydropeptidase 1, EC 3.4.13.19) has been widely studied since it was first purified from porcine kidney brush border membrane. It was reported that RDPase activity in urine samples of acute and chronic renal failure patients decreases. Nitric oxide (NO) is a highly reactive free radical involved in a number of physiological and pathological processes. NO is able to act in a dual mode, leading either to induction of apoptosis or to blunted execution of programmed cell death. NO inhibited the RDPase release from porcine renal proximal tubules, which could be blocked by L‐NAME. Chitosan, the linear polymer of D‐glucosamine in β(1?4) linkage, not only reversed the decreased RDPase release by NO but also increased NO production in the proximal tubule cells. The stimulatory effect of NO on RDPase release from proximal tubules in the presence of chitosan must be different from the previously proposed mechanism of RDPase release via NO signaling pathway. Chitosan...