Nitric oxide synthase regulatory sites. Phosphorylation by cyclic AMP-dependent protein kinase, protein kinase C, and calcium/calmodulin protein kinase; identification of flavin and calmodulin binding sites

Cross-talk between constitutive and inducible NO synthase: an update

Inducible nitric oxide synthase (iNOS) is expressed upon exposure of some cell types to bacterial lipopolysaccharides (LPS) and/or a variety of proinflammatory cytokines. The authors present an overview of some of the recent findings further supporting the notion that this response takes place after an early decline in constitutive nitric oxide (NO) levels (i.e., NO released by constitutive NOS, cNOS). This response is indeed critical for allowing activation of the transcription factor NF-kappaB. Thus, generation of NO by cNOS represents a limiting factor for iNOS expression. Some of the physiological and pathological implications of the cross-talk between these two NOS isoforms are discussed. In addition, the results of recent studies are summarized, suggesting possible mechanisms whereby LPS and/or proinflammatory cytokines may cause inhibition of cNOS.

Activity-dependent heterogeneous populations of nitric oxide synthase neurons in the rat dorsal raphe nucleus

The brainstem dorsal raphe nucleus (DRN) contains an abundant distribution of nitric oxide (NO) synthase (NOS)-containing neuronal profiles in two distinct populations: faint- and intense-immunoreactive cells in midline (ventromedial and dorsomedial) and lateral wing subregions, respectively. This study tested the hypothesis that different functional dynamics underlie the topography of NOS-containing cells in the DRN rostrocaudal and mediolateral neuraxis by using a capsaicin challenge paradigm (50 mg/kg, subcutaneous). Compared with vehicle, capsaicin significantly and preferentially increased nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d, an index of constitutive NOS) reactivity in the rostral midline and caudal lateral wing subregions. Furthermore, capsaicin activated more Fos-positive cells than vehicle within all subregions of the DRN but with a caudal versus rostral predominance in activation pattern. In addition, a high proportion of capsaicin-induced Fos cells in the midline but almost none in lateral wing stained for NADPH-d. These observations suggest the existence of two functionally distinct populations of NOS neurons in the DRN. Furthermore, capsaicin increased galanin immunoreactivity with predominant staining in cell soma and fiber processes in midline and lateral wing subregions of the nucleus, respectively. The total capsaicin-induced galanin immunoreactivity was higher in rostral versus caudal DRN, and a high proportion of galanin-positive cells in the midline also contained NADPH-d and neuronal NOS, thus suggesting a potential NO-galanin interaction in these neurons. The differential pattern of Fos/NADPH-d colocalization across the nucleus suggests that midline and lateral wing NOS neurons of the DRN express their neuromodulatory actions on discrete efferent targets via different intracellular mechanisms.

Nitric Oxide Synthase (NOS) Characterization in Leishmania amazonensis Axenic Amastigotes

BACKGROUND

Although Leishmania virulence may be modulated by environmental and genetic factors of their mammalian hosts and sand fly vectors, molecular determinants of Leishmania sp. are the key elements. This work evidences that Leishmania amazonensis axenic amastigotes produce comparatively more NO than infective promastigotes.

METHODS

A soluble NOS was purified from L. amazonensis axenic amastigotes by affinity chromatography (2',5'-ADP-agarose), and on SDS-PAGE the enzyme migrates as a single protein band.

RESULTS

The presence of a constitutive NOS was detected through immunofluorescence using antibody against neuronal NOS (nNOS) and in NADPH consumption assays.

CONCLUSIONS

The present data show that NOS is prominent in axenic amastigote preparations, suggesting an association with the infectivity and/or an escaping mechanism of the parasite. The relationship between the NO-generating systems in the parasite and in their host cell warrants further investigation.

Nitric oxide biosynthesis by Leishmania amazonensis promastigotes containing a high percentage of metacyclic forms

Due to the diversity of its physiological and pathophysiological functions and general ubiquity, the study of nitric oxide (NO) has become of great interest. In this work, it was demonstrated that Leishmania amazonensis promastigotes produces NO, a free radical synthesized from L: -arginine by nitric oxide synthase (NOS). A soluble NOS was purified from L. amazonensis promastigotes by affinity chromatography (2', 5'-ADP-agarose) and on SDS-PAGE the enzyme migrates as a single protein band of 116.2 (+/-6) kDa. Furthermore, the presence of a constitutive NOS was detected through indirect immunofluorescence using anti-cNOS and in NADPH consumption assays. The present work show that NO production, detected as nitrite in culture supernatant, is prominent in promastigotes preparations with high number of metacyclic forms, suggesting an association with the differentiation and the infectivity of the parasite.

Possible involvement of the spinal nitric oxide/cGMP pathway in vincristine-induced painful neuropathy in mice

The mechanisms that underlie the development of vincristine-induced painful neuropathy are poorly understood. The nitric oxide (NO)-cGMP pathway has been reported to be involved in the spinal transmission of nociceptive information. In the present study, we examined whether alterations in spinal nociceptive processing via the NO-cGMP pathway contribute to vincristine-induced painful neuropathy in mice. Mice were intraperitoneally treated with vincristine at a dose of 0.05 mg/kg 1 day after the measurement of pre-drug latency in the tail-flick test, and then treated with a dose of 0.125 mg/kg twice a week for 6 weeks. In vincristine-treated mice, a significant decrease in tail-flick latencies developed at 4 weeks after treatment. Pretreatment with L-arginine (30-300 mg/kg, s.c.), a substrate of NO synthase (NOS), dose-dependently increased the tail-flick latencies in vincristine-treated mice. The L-arginine-induced increase in tail-flick latencies in vincristine-treated mice was completely reversed by i.t. pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 3-30 nmol), a NOS inhibitor. Furthermore, i.t. pretreatment with 8-bromoguanosine 3', 5'-cyclic monophosphate (8-Br-cGMP, 0.3-3.0 nmol), a membrane-permeable cGMP analog, dose-dependently increased the tail-flick latencies in vincristine-treated mice. The contents of NO metabolites, cGMP and protein levels of neuronal NOS in the spinal cord in vincristine-treated mice were significantly reduced compared to those in vehicle-treated naive mice. These results indicate that dysfunction of the L-arginine/NO/cGMP cascade in the spinal cord may trigger vincristine-induced thermal hyperalgesia in mice.

Lead neurotoxicity: From exposure to molecular effects

The effects of lead (Pb(2+)) on human health have been recognized since antiquity. However, it was not until the 1970s that seminal epidemiological studies provided evidence on the effects of Pb(2+) intoxication on cognitive function in children. During the last two decades, advances in behavioral, cellular and molecular neuroscience have provided the necessary experimental tools to begin deciphering the many and complex effects of Pb(2+) on neuronal processes and cell types that are essential for synaptic plasticity and learning and memory in the mammalian brain. In this review, we concentrate our efforts on the effects of Pb(2+) on glutamatergic synapses and specifically on the accumulating evidence that the N-methyl-D-aspartate type of excitatory amino acid receptor (NMDAR) is a direct target for Pb(2+) effects in the brain. Our working hypothesis is that disruption of the ontogenetically defined pattern of NMDAR subunit expression and NMDAR-mediated calcium signaling in glutamatergic synapses is a principal mechanism for Pb(2+)-induced deficits in synaptic plasticity and in learning and memory documented in animal models of Pb(2+) neurotoxicity. We provide an introductory overview of the magnitude of the problem of Pb(2+) exposure to bring forth the reality that childhood Pb(2+) intoxication remains a major public health problem not only in the United States but worldwide. Finally, the latest research offers some hope that the devastating effects of childhood Pb(2+) intoxication in a child's ability to learn may be reversible if the appropriate stimulatory environment is provided.

Male castration increases neuronal nitric oxide synthase activity in the rat mesenteric artery through protein kinase C activation

The objective of the present study was to assess the effect of endogenous male sex hormones on the activity of protein kinase C (PKC), as well as the regulatory effect of this kinase on the neuronal nitric oxide (NO) release induced by electrical field stimulation (EFS; 200 mA; 0.3 ms; 1-16 Hz). For this purpose, superior mesenteric arteries from control and orchidectomized male Sprague-Dawley rats were used. PKC activity was greater in arteries from orchidectomized than control rats. Basal and EFS-induced NO release was similar in arteries from both groups despite the lower nNOS expression in arteries from orchidectomized rats. Phorbol 12,13-dibutyrate (PDBu), a PKC activator, EFS-induced NO release was higher in arteries from control compared to orchidectomized rats. Calphostin C, a non-selective PKC inhibitor, or Gö6976, a PKC inhibitor partially selective for conventional isoforms,abolished the EFS-induced NO release in arteries from control animals, while it was decreased in arteries from orchidectomized animals. The PKCzeta pseudosubstrate inhibitor decreased EFS-induced NO release equally in both groups. The NO synthase (NOS) inhibitor Nomega-nitro-L-arginine-methyl ester (L-NAME) enhanced the EFS-elicited contractions in arteries from both groups. Calphostin C increased the contractions elicited by EFS in arteries from control and orchidectomized rats. This increase was further enhanced by calphostin C plus L-NAME only in orchidectomized rats. PDBu reduced EFS-induced contraction in arteries from controls but did not affect it in orchidectomized rats. The further addition of L-NAME increased the responses in both types of arteries. These results show that PKC activity is enhanced in mesenteric arteries from orchidectomized rats, which may be the responsible for the greater nNOS activity in these arteries. Conventional and atypical PKCzeta isoforms positively regulate nNOS activity in arteries from both control and orchidectomized rats, but the contribution of conventional PKC isoforms to enhanced nNOS activity seems to be greater in arteries from orchidectomized rats.

Lead effects on non-adrenergic non-cholinergic relaxations in the rat gastric fundus

The effect of lead exposure on non-adrenergic non-cholinergic (NANC) relaxations in rat gastric fundus was evaluated in this work. Wistar rats were divided into four groups: The control group received tap water and the three other received 0.008% of lead acetate in their drinking water for 15, 30 and 120 days. NANC relaxations induced by electrical field stimulation (0.5-8 Hz, 1 ms, 60 V) of gastric fundus strips was inhibited in all groups treated with lead. The strips from groups, control and 120 days of lead treatment (LEAD 120), were incubated with L-NOARG (100 microM). The presence of this blocker did not produce any additional inhibition. Sodium nitroprusside (10(-10)-10(-6) M) and 8-Br-GMPc (3 x 10(-8)-3 x 10(-4) M) produced dose-dependent relaxations in strips of both groups control and LEAD 120, however, in the LEAD 120, the potencies were significantly reduced from 7.32 +/- 0.05 to 6.40 +/- 0.09 (n = 5) and 4.26 +/- 0.06 to 3.69 +/- 0.05 (n = 5), respectively. Our data suggest that the chronic exposure to lead inhibits NANC relaxations probably by modulating NO release from NANC nerves and/or by interacting with intracellular transducer mechanisms in rat gastric fundus.

Altered nitric oxide synthase and PKC activities in cerebellum of gamma-irradiated neonatal rats

In this study, we show that one single dose of gamma-irradiation at birth induces an inhibition of the cerebellar calcium dependent nitric oxide synthase (NOS) activity, probably correlated to the motor abnormalities and the disarrangement in the cerebellar cytoarchitecture observed in adult rats. This decrease in calcium dependent NOS activity could be associated with an increased protein kinase C (PKC) activity. PKC inhibition partially restores calcium dependent NOS activity, indicating that PKC activity could be negatively modulating the catalytic activity of calcium dependent NOS. These findings suggest that a decrease in nitric oxide (NO) production and the related increase in PKC activity could be intracellular events that participate in the onset of motor and cerebellar abnormalities induced by postnatal gamma-irradiation at early stages of life.

1400W, a potent selective inducible NOS inhibitor, improves histopathological outcome following traumatic brain injury in rats

There are conflicting data regarding the role of nitric oxide (NO) produced by inducible NO synthase (iNOS) in the pathophysiology of traumatic brain injury (TBI). In this report, we evaluated the effect of a potent selective (iNOS) inhibitor, 1400W, on histopathological outcome following TBI in a rat model of lateral fluid percussion brain injury. First, to design an appropriate treatment protocol, the parallel time courses of iNOS and neuronal NOS (nNOS) gene expression, protein synthesis, and activity were investigated. Early induction of iNOS gene was observed in the cortex of injured rats, from 6 to 72 h with a peak at 24 h. Similarly, iNOS protein was detected from 24 to 72 h and de novo synthesized iNOS was functionally active, as measured by Ca2+-independent NOS activity. The kinetic studies of nNOS showed discrepancies, since nNOS gene expression and protein synthesis were constant in the cortex of injured rats from 24 to 72 h, while Ca2+-dependent constitutive NOS activity was markedly decreased at 24 h, persisting up to 72 h. Second, treatment with 1400W, started as a bolus of 20 mg kg-1 (s.c.) at 18 h post-TBI, followed by s.c.-infusion at a rate of 2.2 mg kg-1 h-1 between 18 and 72 h, reduced by 64% the brain lesion volume at 72 h. However, the same treatment paradigm initiated 24 h post-TBI did not have any effect. In conclusion, administration of a selective iNOS inhibitor, 1400W, even delayed by 18 h improves histopathological outcome supporting a detrimental role for iNOS induction after TBI.

Cyclosporin-A Inhibits Constitutive Nitric Oxide Synthase Activity and Neuronal and Endothelial Nitric Oxide Synthase Expressions after Spinal Cord Injury in Rats

Nitric oxide (NO) plays a role in the pathophysiology of spinal cord injury (SCI). NO is produced by three types of nitric oxide synthase (NOS) enzymes: The constitutive Ca2+/calmodulin-dependent neuronal NOS (nNOS) and endothelial NOS (eNOS) isoforms, and the inducible calcium-independent isoform (iNOS). During the early stages of SCI, nNOS and eNOS produce significant amounts of NO, therefore, the regulation of their activity and expression may participate in the damage after SCI. In the present study, we used Cyclosporin-A (CsA) to further substantiate the role of Ca-dependent NOS in neural responses associated to SCI. Female Wistar rats were subjected to SCI by contusion, and killed 4 h after lesion. Results showed an increase in the activity of constitutive NOS (cNOS) after lesion, inhibited by CsA (2.5 mg/kg i.p.). Western blot assays showed an increased expression of both nNOS and eNOS after trauma, also antagonized by CsA administration.

eNOS, nNOS, cGMP and protein kinase G mediate the inhibitory effect of pancreastatin, a chromogranin A-derived peptide, on growth and proliferation of hepatoma cells

Pancreastatin (PST), a chromogranin A-derived peptide, has an anti-insulin metabolic effect and inhibits growth and proliferation by producing nitric oxide (NO) in HTC rat hepatoma cells. When NO production is blocked, a proliferative effect prevails due to the activation a Galphaq/11-phospholipase C-beta (PLC-beta) pathway, which leads to an increase in [Ca2+]i, protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activation. The aim of the present study was to investigate the NO synthase (NOS) isoform that mediates these effects of PST on HTC hepatoma cells and the possible roles of cyclic GMP (cGMP) and cGMP-dependent protein kinase. DNA and protein synthesis in response to PST were measured as [3H]-thymidine and [3H]-leucine incorporation in the presence of various pharmacological inhibitors: N-monomethyl-L-arginine (NMLA, nonspecific NOS inhibitor), L-NIO (endothelial nitric oxide synthase (eNOS) inhibitor), espermidine (neuronal nitric oxide synthase (nNOS) inhibitor), LY83583 (guanylyl cyclase inhibitor), and KT5823 (protein kinase G inhibitor, (PKG)). L-NIO, similarly to NMLA, reverted the inhibitory effect of PST on hepatoma cell into a stimulatory effect on growth and proliferation. Nevertheless, espermidine also prevented the inhibitory effect of PST, but there was no stimulation of growth and proliferation. When guanylyl cyclase activity was blocked, there was again a reversion of the inhibitory effect into a stimulatory action, suggesting that the effect of NO was mediated by the production of cGMP. PKG inhibition prevented the inhibitory effect of PST, but there was no stimulatory effect. Therefore, the inhibitory effect of PST on growth and proliferation of hepatoma cells may be mainly mediated by eNOS activation. In turn, the effect of NO may be mediated by cGMP, whereas other pathways in addition to PKG activation seem to mediate the inhibition of DNA and protein synthesis by PST in HTC hepatoma cells.

Endogenous prostacyclin increases neuronal nitric oxide release in mesenteric artery from spontaneously hypertensive rats

The aim of this study was to analyse the possible influence of endogenous prostacyclin on neuronal nitric oxide (NO) release induced by electrical field stimulation in mesenteric arteries from spontaneously hypertensive rats (SHR). Preincubation with the prostacyclin synthesis inhibitor tranylcypromine decreased NO release induced by electrical field stimulation, which was reversed by exogenous prostacyclin. Preincubation with tranylcypromine increased basal and electrical field stimulation-induced [3H]noradrenaline release. The nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl esther (L-NAME) increased the vasoconstrictor response induced by electrical field stimulation. In the presence of tranylcypromine, L-NAME did not modify the vasoconstrictor response induced by electrical field stimulation. In the presence of tranylcypromine and prostacyclin, LNAME increased the vasoconstrictor response to electrical field stimulation. These results indicate that endogenous prostacyclin positively modulates the neuronal NO release induced by electrical field stimulation and that this neuronal NO participates in the regulation of the vasomotor response.

Inhibition of calcium-calmodulin kinase restores nitric oxide production and signaling in submandibular glands of a mouse model of salivary dysfunction

Nitric oxide is an intracellular and diffusible messenger of neurotransmitters involved in salivary secretion, as well as an inflammatory mediator in salivary gland diseases. It is synthesized by three different isoforms of nitric oxide synthase (NOS), each subject to a fine transcriptional, post-transcriptional and/or post-translational regulation. Our purpose was to study the possible mechanisms leading to NOS downregulation in submandibular glands of normal mice and in the nonobese diabetic (NOD) mouse model of salivary dysfunction with lower NOS activity. NOS activity and cGMP accumulation were determined by radioassays in submandibular glands of both mice in the presence of the protein kinase inhibitors KN-93 and bisindolylmaleimide. NOS I mRNA and protein expression and localization were assessed by RT-PCR, Western blot and immunohistochemistry. A downregulatory effect of calcium-calmodulin kinase II (CaMK II) on NOS activity in submandibular glands of both NOD and BALB/c mice was observed. Our results are consistent with a physiological regulation of NOS activity by this kinase but not by PKC in normal BALB/c mice. They are also supportive of a role for CaMK II in the lack of detectable NOS activity in submandibular glands of NOD mice. KN-93 also restored cGMP accumulation in NOD submandibular glands. The downregulation of NOS in NOD mice seems to be mainly mediated by this kinase rather than the result of a lower expression or different cellular localization of the enzyme. It was not related to different substrate or cofactors availability either.

Nitric oxide control of cardiac function: is neuronal nitric oxide synthase a key component?

Nitric oxide (NO) has been shown to regulate cardiac function, both in physiological conditions and in disease states. However, several aspects of NO signalling in the myocardium remain poorly understood. It is becoming increasingly apparent that the disparate functions ascribed to NO result from its generation by different isoforms of the NO synthase (NOS) enzyme, the varying subcellular localization and regulation of NOS isoforms and their effector proteins. Some apparently contrasting findings may have arisen from the use of non-isoform-specific inhibitors of NOS, and from the assumption that NO donors may be able to mimic the actions of endogenously produced NO. In recent years an at least partial explanation for some of the disagreements, although by no means all, may be found from studies that have focused on the role of the neuronal NOS (nNOS) isoform. These data have shown a key role for nNOS in the control of basal and adrenergically stimulated cardiac contractility and in the autonomic control of heart rate. Whether or not the role of nNOS carries implications for cardiovascular disease remains an intriguing possibility requiring future study.

Calcium/calmodulin-dependent protein kinase I inhibits neuronal nitric-oxide synthase activity through serine 741 phosphorylation

We demonstrate here that neuronal nitric-oxide synthase (nNOS) is phosphorylated and inhibited by a constitutively active form of Ca2+/calmodulin (CaM)-dependent protein kinase I (CaM-K I1-293). Substitution of Ser741 to Ala in nNOS blocked the phosphorylation and the inhibitory effect. Mimicking phosphorylation at Ser741 by Ser to Asp mutation resulted in decreased binding of and activation by CaM, since the mutation was within the CaM-binding domain. CaM-K I1-293 gave phosphorylation of nNOS at Ser741 in transfected cells, resulting in 60-70% inhibition of nNOS activity. Wild-type CaM-K I also did phosphorylate nNOS at Ser741 in transfected cells, but either CaM-K II or CaM-K IV did not. These results raise the possibility of a novel cross-talk between nNOS and CaM-K I through the phosphorylation of Ser741 on nNOS.

A role for l-glutamate ionotropic receptors in the development of rat neurogenic pulmonary edema

The present study was undertaken to evaluate possible roles of L-glutamate ionotropic receptors in neurogenic pulmonary edema. Perfusion of L-glutamate into the fourth ventricles of rats increased nitric oxide (NO) signals in the efflux solution concentration-dependently, significantly reducing both the occurrence and severity of neurogenic pulmonary edema. This effect was completely reversed by prior intracisternal injection of an NO synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), or an N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine maleate (MK-801), and partially by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a 2-amino-3-hydroxy-5-methyl-4-isoxazol propionic acid (AMPA)/kainic acid receptor antagonist. Administration of MK-801 or CNQX alone, without L-glutamate, almost completely prevented neurogenic pulmonary edema development. These results suggest that endogenous L-glutamate may facilitate underlining disease process, whereas L-glutamate exogenously applied into the fourth ventricle may have an inhibitory action via release of NO, through ionotropic receptors.

Postsynaptic production of nitric oxide implicated in long-term depression at the mature amphibian (Bufo marinus) neuromuscular junction

We report here evidence for endogenous NO signalling in long-term (>1 h) synaptic depression at the neuromuscular junction induced by 20 min of 1 Hz nerve stimulation. Synaptic depression was characterized by a 46% reduction in the end-plate potential (EPP) amplitude and a 21% decrease in miniature EPP (MEPP) frequency, but no change to MEPP amplitude, indicating a reduction in evoked quantal release. Both the membrane-impermeant NO scavenger cPTIO and the NOS inhibitor L-NAME blocked depression, suggesting that it is induced by NO originating from a source outside the terminal. The depression was dependent on activation of muscle-type, but not neuronal-type, nAChRs and was still observed when Ca2+ release from the sarcoplasmic reticulum and muscle contraction were blocked with dantrolene. These data suggest that the depression depends on transmission, but not muscle contraction. The calcineurin inhibitors cyclosporin A and FK506, as well as ODQ, an inhibitor of NO-sensitive soluble guanylyl cyclase, Rp-8-pCPT-cGMPS, an inhibitor of cGMP-dependent protein kinase, and the calmodulin antagonist phenoxybenzamine also blocked depression. We propose that low frequency synaptic transmission leads to production of NO at the synapse and depression of transmitter release via a cGMP-dependent mechanism. The NO could be generated either directly from the muscle, or possibly from the Schwann cell in response to an unidentified muscle-derived messenger. We showed that the long-lasting depression of transmitter release was due to sustained activity of the NO signalling pathway, and suggest dephosphorylation of NOS by calcineurin as the basis for continued NO production.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

The role of nitric oxide synthases in the sleep responses to tumor necrosis factor-alpha

It is well established that cytokines such as tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta) are involved in physiological sleep regulation, yet their downstream somnogenic mechanisms remain largely uninvestigated. Nitric oxide (NO) is an effector molecule for some TNFalpha actions. Neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) gene knockout (KO) mice sleep differently than their respective controls. In this study, we tested the hypothesis that NO mediates TNFalpha-induced sleep using iNOS and nNOS KO mice and their corresponding wild-type controls. Systemic administration of TNFalpha increased non-rapid eye movement sleep (NREMS) in the two control strains and in the iNOS KO mice during the first 4 h post-injection but failed to increase NREMS in nNOS KO mice. Rapid eye movement sleep (REMS) was suppressed by TNFalpha in nNOS controls but not in the other strains examined. The results suggest that TNFalpha affects sleep, in part, through nNOS.

The function of the small insertion in the hinge subdomain in the control of constitutive mammalian nitric-oxide synthases

Control of nitric oxide (NO) synthesis in the constitutive nitric-oxide synthases (NOS) by calcium/calmodulin is exerted through the regulation of electron transfer from NADPH through the reductase domains. This process has been shown previously to involve the calmodulin binding site, the autoinhibitory insertion in the FMN binding domain, and the C-terminal tail. Smaller sequence elements also appear to correlate with control. Although some of these elements appear well positioned to function in control, they are poorly conserved; their role in control is neither well established nor defined by available information. In this study mutations have been induced in the small insertion of the hinge subdomain, which has been shown recently to form a beta hairpin in structural studies of the neuronal NOS reductase domains adjacent to the calmodulin site and the autoinhibitory element. Modification of the small insertion in neuronal NOS tends to increase cytochrome c reduction but not NO synthetic activity; some modifications or deletions in the corresponding region in endothelial NOS modestly increase activity under some conditions. Unexpectedly, some minor changes in the sequence introduce a loss in the content of heme relative to flavin cofactors. Taken together, these results suggest that the small insertion protects the calmodulin binding site and that it may be a modulator of NOS activity.

Activity-driven sharpening of the retinotectal projection: the search for retrograde synaptic signaling pathways

Patterned visual activity, acting via NMDA receptors, refines developing retinotectal maps by shaping individual retinal arbors. Because NMDA receptors are postsynaptic but the retinal arbors are presynaptic, there must be retrograde signals generated downstream of Ca(++) entry through NMDA receptors that direct the presynaptic retinal terminals to stabilize and grow or to withdraw. This review defines criteria for retrograde synaptic messengers, and then applies them to the leading candidates: nitric oxide (NO), brain-derived neurotrophic factor (BDNF), and arachidonic acid (AA). NO is not likely to be a general mechanism, as it operates only in selected projections of warm blooded vertebrates to speed up synaptic refinement, but is not essential. BDNF is a neurotrophin with strong growth promoting properties and complex interactions with activity both in its release and receptor signaling, but may modulate rather than mediate the retrograde signaling. AA promotes growth and stabilization of synaptic terminals by tapping into a pre-existing axonal growth-promoting pathway that is utilized by L1, NCAM, N-cadherin, and FGF and acts via PKC, GAP43, and F-actin stabilization, and it shares some overlap with BDNF pathways. The actions of both are consistent with recent demonstrations that activity-driven stabilization includes directed growth of new synaptic contacts. Certain nondiffusible factors (synapse-specific CAMs, ephrins, neurexin/neuroligin, and matrix molecules) may also play a role in activity-driven synapse stabilization. Interactions between these pathways are discussed.

AKT participates in endothelial dysfunction in hypertension

BACKGROUND

In hypertension, reduced nitric oxide production and blunted endothelial vasorelaxation are observed. It was recently reported that AKT phosphorylates and activates endothelial nitric oxide synthase and that impaired kinase activity may be involved in endothelial dysfunction.

METHODS AND RESULTS

To identify the physiological role of the kinase in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), we used adenoviral vectors to transfer the human AKT1 gene selectively to the common carotid endothelium. In vitro, endothelial vasorelaxations to acetylcholine, isoproterenol, and insulin were blunted in control carotids from SHR compared with WKY rats, and human AKT1 overexpression corrected these responses. Similarly, blood flow assessed in vivo by Doppler ultrasound was reduced in SHR compared with WKY carotids and normalized after AKT1 gene transfer. In primary cultured endothelial cells, we evaluated AKT phosphorylation, activity, and compartmentalization and observed a mislocalization of the kinase in SHR.

CONCLUSIONS

We conclude that AKT participates in the settings of endothelial dysfunction in SHR rats by impaired membrane localization. Our data suggest that AKT is involved in endothelium dysfunction in hypertension.

Postsynaptic density protein 95 mediates Ca2+/calmodulin-dependent protein kinase II-activated serine phosphorylation of neuronal nitric oxide synthase during brain ischemia in rat hippocampus

Recent study has indicated that postsynaptic density protein 95 (PSD95) promotes Ca2+/calmodulin-dependent protein kinase II (CaMKII)-mediated serine phosphorylation of neuronal nitric oxide synthase (nNOS). To investigate whether PSD95 is involved in the brain ischemia-induced enhancement of serine phosphorylation of nNOS by CaMKII in rat hippocampus, we examined the interactions among CaMKIIalpha, PSD95 and nNOS, and the effects of suppression of PSD95 expression on both the increased serine phosphorylation of nNOS and the interactions mentioned above by immunoprecipitation and immunoblotting. The following results were observed: (1) brain ischemia increased markedly the interactions of CaMKIIalpha and nNOS with PSD95. (2) Intracerebroventricular infusion of PSD95 antisense oligodeoxynucleotides, but not missense oligodeoxynucleotides or vehicle, not only significantly decreased the protein level of PSD95 but also attenuated the elevated serine phosphorylation of nNOS and the interactions among CaMKIIalpha, PSD95 and nNOS induced by 15 min ischemia. These data suggested that PSD95 is important for facilitating nNOS serine phosphorylation by CaMKII.

Calcineurin regulation of neuronal plasticity

From the most basic of nervous systems to the intricate circuits found within the human brain, a fundamental requirement of neuronal function is that it be malleable, altering its output based upon experience. A host of cellular proteins are recruited for this purpose, which themselves are regulated by protein phosphorylation. Over the past several decades, research has demonstrated that the Ca(2+) and calmodulin-dependent protein phosphatase calcineurin (protein phosphatase 2B) is a critical regulator of a diverse array of proteins, leading to both short- and long-term effects on neuronal excitability and function. This review describes many of the influences of calcineurin on a variety of proteins, including ion channels, neurotransmitter receptors, enzymes, and transcription factors. Intriguingly, due to the bi-directional influences of Ca(2+) and calmodulin on calcineurin activity, the strength and duration of particular stimulations may cause apparently antagonistic functions of calcineurin to work in concert.

Protein Kinase C Masks Nitric Oxide Synthase Activity in Vascular Smooth Muscle under Basal Conditions

Under basal conditions there is no observable nitric oxide synthase (NOS) activity in vascular smooth muscle (VSM). Pretreatment of endothelium-denuded aortic rings from Sprague-Dawley rats with 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), (0.1 micromol/L) significantly attenuated phenylephrine (PE)-induced contractile responses in a dose-dependent manner. In the presence of 10 micromol/L Nomega-nitro-L-arginine (L-NNA) or 0.1 mmol/L aminoguanidine (AG), the inhibition of contractions at 10 nmol/L PE by H-7 was blocked by 88% or 52%, respectively. The blockade by antagonists was completely reversed by l-arginine but not by d-arginine, and alone they did not significantly alter PE-induced contraction of endothelium-denuded aorta. Methylene blue (MB, 50 micromol/L) also inhibited the action of H-7. The inhibitory effect of H-7 occurred after 5 minutes and was reversible. PE-induced contraction was also inhibited by the selective protein kinase C inhibitors calphostin C (10 micromol/L), and bisindolylmaleimide IV (Bis-IV, 10 micromol/L), but not by the selective protein kinase A inhibitor H-89 (0.1 micromol/L). These results indicate protein kinase C inhibits NOS activity in VSM under basal conditions. Incubation of tissues with either H-7 or calphostin C stimulates NO production, and immunocytochemical studies reveal the presence of NOS in VSM under basal conditions.

Nitric oxide in brain: diffusion, targets and concentration dynamics in hippocampal subregions

Nitric oxide (NO(*)) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO(*) concentration is translated into a cellular signal. From our current knowledge of biological synthesis and decay, the kinetics and mechanisms that determine NO(*) concentration dynamics in tissues are poorly understood. Generally, NO(*) mediates its effects by stimulating (e.g., guanylate cyclase) or inhibiting (e.g., cytochrome oxidase) transition metal-containing proteins and by post-translational modification of proteins (e.g., formation of nitrosothiol adducts). The borderline between the physiological and pathological activities of NO(*) is a matter of controversy, but tissue redox environment, supramolecular organization and compartmentalisation of NO(*) targets are important features in determining NO(*) actions. In brain, NO(*) synthesis in the dependency of glutamate NMDA receptor is a paradigmatic example; the NMDA-subtype glutamate receptor triggers intracellular signalling pathways that govern neuronal plasticity, development, senescence and disease, suggesting a role for NO(*) in these processes. Measurements of NO(*) in the different subregions of hippocampus, in a glutamate NMDA receptor-dependent fashion, by means of electrochemical selective microsensors illustrate the concentration dynamics of NO(*) in the sub-regions of this brain area. The analysis of NO(*) concentration-time profiles in the hippocampus requires consideration of at least two interrelated issues, also addressed in this review. NO(*) diffusion in a biological medium and regulation of NO(*) activity.

Downregulation of nitric oxide formation by cytosolic phospholipase A2-released arachidonic acid

Exposure of PC12 cells to A23187 or thapsigargin caused a concentration-dependent release of arachidonic acid (AA) mediated by cytosolic phospholipase A2 (PLA2). Under the same conditions, however, analysis of nitric oxide (NO) formation revealed that activation of NO synthase (NOS) is best described by a bell-shaped curve. Reduced detection of NO observed at increasing A23187 or thapsigargin concentrations was not due to formation of peroxynitrite or to activation of NO-consuming processes, but rather to AA-dependent inhibition of NOS activity. Furthermore, NO formation observed under optimal conditions for NOS activity was suppressed by AA as well as by the PLA2 activator melittin. Finally, the effects of AA were not the consequence of direct enzyme inhibition, because this lipid messenger failed to inhibit formation of NO by purified neuronal NOS, but were mediated by an AA-dependent signaling and not by downstream products of the cyclooxygenase and lipoxygenase pathways. In conclusion, the present study underscores a novel mechanism whereby endogenous, or exogenous, AA promotes inhibition of NOS activity. Because AA is generated in response to various agonists acting on membrane receptors and extensively released in inflammatory conditions, these findings have important physiopathological implications.

Bidirectional regulation of neuronal nitric-oxide synthase phosphorylation at serine 847 by the N-methyl-D-aspartate receptor

At glutamatergic synapses, the scaffolding protein PSD95 links the neuronal isoform of nitric-oxide synthase (nNOS) to the N-methyl-d-aspartate (NMDA) receptor. Phosphorylation of nNOS at serine 847 (Ser(847)) by the calcium-calmodulin protein kinase II (CaMKII) inhibits nNOS activity, possibly by blocking the binding of Ca(2+)-CaM. Here we show that the NMDA mediates a novel bidirectional regulation of Ser(847) phosphorylation. nNOS phosphorylated at Ser(847) colocalizes with the NMDA receptor at spines of cultured hippocampal neurons. Treatment of neurons with 5 microm glutamate stimulated CaMKII phosphorylation of nNOS at Ser(847), whereas excitotoxic concentrations of glutamate, 100 and 500 microm, induced Ser(847)-PO(4) dephosphorylation by protein phosphatase 1. Strong NMDA receptor stimulation was likely to activate nNOS under these conditions because protein nitration to form nitrotyrosine, a marker of nNOS activity, correlated in individual neurons with Ser(847)-PO(4) dephosphorylation. Of particular note, stimulation with low glutamate that increased phosphorylation of nNOS at Ser(847) could be reversed by subsequent high glutamate treatment which induced dephosphorylation. The reversibility of NMDA receptor-induced phosphorylation at Ser(847) by different doses of glutamate suggests two mechanisms with opposite effects: 1). a time-dependent negative feedback induced by physiological concentrations of glutamate that limits nNOS activation and precludes the overproduction of NO; and 2). a pathological stimulation by high concentrations of glutamate that leads to unregulated nNOS activation and production of toxic levels of NO. These mechanisms may share pathways, respectively, with NMDA receptor-induced forms of synaptic plasticity and excitotoxicity.

Key role of PLC-gamma in EGF protection of epithelial barrier against iNOS upregulation and F-actin nitration and disassembly

Upregulation of inducible nitric oxide synthase (iNOS) is key to oxidant-induced disruption of intestinal (Caco-2) monolayer barrier, and EGF protects against this disruption by stabilizing the cytoskeleton. PLC-gamma appears to be essential for monolayer integrity. We thus hypothesized that PLC-gamma activation is essential in EGF protection against iNOS upregulation and the consequent cytoskeletal oxidation and disarray and monolayer disruption. Intestinal cells were transfected to stably overexpress PLC-gamma or to inhibit its activation and were then pretreated with EGF +/- oxidant (H2O2). Wild-type (WT) intestinal cells were treated similarly. Relative to WT monolayers exposed to oxidant, pretreatment with EGF protected monolayers by: increasing native PLC-gamma activity; decreasing six iNOS-related variables (iNOS activity/protein, NO levels, oxidative stress, actin oxidation/nitration); increasing stable F-actin; maintaining actin stability; and enhancing barrier integrity. Relative to WT cells exposed to oxidant, transfected monolayers overexpressing PLC-gamma (+2.3-fold) were protected, as indicated by decreases in all measures of iNOS-driven pathway and enhanced actin and barrier integrity. Overexpression-induced inhibition of iNOS was potentiated by low doses of EGF. Stable inhibition of PLC-gamma prevented all measures of EGF protection against iNOS upregulation. We conclude that 1) EGF protects against oxidative stress disruption of intestinal barrier by stabilizing F-Actin, largely through the activation of PLC-gamma and downregulation of iNOS pathway; 2) activation of PLC-gamma is by itself essential for cellular protection against oxidative stress of iNOS; and 3) the ability to suppress iNOS-driven reactions and cytoskeletal oxidation and disassembly is a novel mechanism not previously attributed to the PLC family of isoforms.

Characteristics of GABA release modified by glutamate receptors in mouse hippocampal slices

The major part of hippocampal innervation is glutamatergic, regulated by inhibitory GABA-releasing interneurons. The modulation of [(3)H]GABA release by ionotropic and metabotropic glutamate receptors and by nitric oxide was here characterized in superfused mouse hippocampal slices. The ionotropic glutamate receptor agonists kainate, N-methyl-D-aspartate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate potentiated the basal GABA release. These effects were blocked by their respective antagonists 6-nitro-7-cyanoquinoxaline-2,3-dione (CNQX), dizocilpine and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulfonamide (NBQX), indicating receptor-mediated mechanisms. The NO-generating compounds S-nitroso-N-acetylpenicillamine (SNAP), sodiumnitroprusside and hydroxylamine enhanced the basal GABA release. Particularly the sodiumnitroprusside-evoked release was attenuated by the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA) and the inhibitor of soluble guanylyl cyclase 1H-(1,2,4)oxadiazolo(4,3a)quinoxalin-1-one (ODQ), indicating the involvement of the NO/cGMP pathway. This inference is corroborated by the enhancing effect of zaprinast, a phosphodiesterase inhibitor, which is known to increase cGMP levels. The K(+)-stimulated hippocampal GABA release was reduced by the groups I and III agonists of metabotropic glutamate receptors (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylate (t-ACPD) and L-(+)-2-amino-4-phosphonobutyrate (L-AP4), which effects were abolished by their respective antagonists (RS)-1-aminoindan-1,5-dicarboxylate (AIDA) and (RS)-2-cyclopropyl-4-phosphonophenylglycine (CPPG), again indicating modification by receptor-mediated mechanisms.

Flow-dependent regulation of endothelial nitric oxide synthase: role of protein kinases

Vascular endothelial cells are directly and continuously exposed to fluid shear stress generated by blood flow. Shear stress regulates endothelial structure and function by controlling expression of mechanosensitive genes and production of vasoactive factors such as nitric oxide (NO). Though it is well known that shear stress stimulates NO production from endothelial nitric oxide synthase (eNOS), the underlying molecular mechanisms remain unclear and controversial. Shear-induced production of NO involves Ca2+/calmodulin-independent mechanisms, including phosphorylation of eNOS at several sites and its interaction with other proteins, including caveolin and heat shock protein-90. There have been conflicting results as to which protein kinases-protein kinase A, protein kinase B (Akt), other Ser/Thr protein kinases, or tyrosine kinases-are responsible for shear-dependent eNOS regulation. The functional significance of each phosphorylation site is still unclear. We have attempted to summarize the current status of understanding in shear-dependent eNOS regulation.

Mechanistic studies on the intramolecular one-electron transfer between the two flavins in the human neuronal nitric-oxide synthase and inducible nitric-oxide synthase flavin domains

Neuronal nitric-oxide synthase (nNOS) differs from inducible NOS (iNOS) in both its dependence on the intracellular Ca2+ concentration and the production rate of NO. To investigate what difference(s) exist between the two NOS flavin domains at the electron transfer level, we isolated the recombinant human NOS flavin domains, which were co-expressed with human calmodulin (CaM). The flavin semiquinones, FADH* and FMNH*, in both NOSs participate in the regulation of one-electron transfer within the flavin domain. Each semiquinone can be identified by a characteristic absorption peak at 520 nm (Guan, Z.-W., and Iyanagi, T. (2003) Arch. Biochem. Biophys. 412, 65-76). NADPH reduction of the FAD and FMN redox centers by the CaM-bound flavin domains was studied by stopped-flow and rapid scan spectrometry. Reduction of the air-stable semiquinone (FAD-FMNH*) of both domains with NADPH showed that the extent of conversion of FADH2/FMNH* to FADH*/FMNH2 in the iNOS flavin domain was greater than that of the nNOS flavin domain. The reduction of both oxidized domains (FAD-FMN) with NADPH resulted in the initial formation of a small amount of disemiquinone, which then decayed. The rate of intramolecular electron transfer between the two flavins in the iNOS flavin domain was faster than that of the nNOS flavin domain. In addition, the formation of a mixture of the two- and four-electron-reduced states in the presence of excess NADPH was different for the two NOS flavin domains. The data indicate a more favorable formation of the active intermediate FMNH2 in the iNOS flavin domain.

Screening for nitric oxide-dependent protein-protein interactions

Because nitric oxide (NO) may be a ubiquitous regulator of cellular signaling, we have modified the yeast two-hybrid system to explore the possibility of NO-dependent protein-protein interactions. We screened for binding partners of procaspase-3, a protein implicated in apoptotic signaling pathways, and identified multiple NO-dependent interactions.Two such interactions, with acid sphingomyelinase and NO synthase, were shown to occur in mammalian cells dependent on endogenous NO. Nitrosylation may thus provide a broad-based mechanism for regulating interactions between proteins. If so, systematic proteomic analyses in which redox state and NO bioavailability are carefully controlled will reveal a large array of novel interactions.

Role of calcineurin in activity-dependent pattern formation in the dorsal lateral geniculate nucleus of the ferret

In the retinogeniculate pathway of the ferret, in addition to the separation of the inputs from the two eyes to form eye-specific layers, there is also an anatomical segregation of the terminal arbors of on-center retinal ganglion cells from the terminal arbors of off-center retinal ganglion cell axons to form on/off sublaminae. Sublamination normally occurs during postnatal weeks 3-4 and requires the activity of retinal afferents, N-methyl-D-aspartate receptors, nitric oxide synthase, and a target of nitric oxide, cyclic guanosine monophosphate. Calcineurin is a calcium/calmodulin dependent serine, threonine protein phosphatase suggested to mediate NMDA-receptor dependent synaptic plasticity in the hippocampus. We have examined whether calcineurin plays a role during on/off sublamination in the dorsal lateral geniculate nucleus (dLGN) of the ferret. Immunohistochemistry showed that calcineurin expression is transiently up-regulated in dLGN cells and neuropil during the period of on/off sublamination. A functional role for calcineurin during sublamination was investigated by blocking the enzyme locally via intracranial infusion of FK506. Treatment with FK506 during postnatal weeks 3-4 disrupted the appearance of sublaminae. These results suggest that calcineurin may play a role during this process of activity-dependent pattern formation in the visual pathway.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Involvement of Ca2+/calmodulin-dependent protein kinase II in endothelial NO production and endothelium-dependent relaxation

Nitric oxide (NO) is synthesized from l-arginine by the Ca(2+)/calmodulin-sensitive endothelial NO synthase (NOS) isoform (eNOS). The present study assesses the role of Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) in endothelium-dependent relaxation and NO synthesis. The effects of three CaMK II inhibitors were investigated in endothelium-intact aortic rings of normotensive rats. NO synthesis was assessed by a NO sensor and chemiluminescence in culture medium of cultured porcine aortic endothelial cells stimulated with the Ca(2+) ionophore A23187 and thapsigargin. Rat aortic endothelial NOS activity was measured by the conversion of l-[(3)H]arginine to l-[(3)H]citrulline. Three CaMK II inhibitors, polypeptide 281-302, KN-93, and lavendustin C, attenuated the endothelium-dependent relaxation of endothelium-intact rat aortic rings in response to acetylcholine, A23187, and thapsigargin. None of the CaMK II inhibitors affected the relaxation induced by NO donors. In a porcine aortic endothelial cell line, KN-93 decreased NO synthesis and caused a rightward shift of the concentration-response curves to A23187 and thapsigargin. In rat aortic endothelial cells, KN-93 significantly decreased bradykinin-induced eNOS activity. These results suggest that CaMK II was involved in NO synthesis as a result of Ca(2+)-dependent activation of eNOS.

Nitric-oxide-mediated regulation of cardiac contractility and stretch responses

In the heart, nitric oxide (NO) is constitutively produced by the vascular and endocardial endothelium, the cardiomyocytes and the autonomic nerves. Whereas stimulation of NO release from the vascular endothelium has consistently been shown to quicken the onset of left ventricular (LV) relaxation and cause a small reduction in peak contraction, the role of myocardial NO production in regulating cardiac function appears to be more complex and controversial. Some studies have shown that non-isoform-specific inhibition of NO synthesis with L-arginine analogues has no effect on basal contraction in LV myocytes. However, others have demonstrated that stimulation of myocardial NO production can offset the increase in contraction in response to a rise in intracellular Ca(2+). Cardiac NO production is also activated by stretch and under these conditions NO has been shown to facilitate the Frank-Starling response and to contribute to the increase in intracellular Ca(2+) transients that mediates the slow increase in contraction in response to stretch (i.e., the Anrep effect). These findings suggest that NO can mediate diverse and even contrasting actions within the myocardium, a notion that is difficult to reconcile with the early description of NO as a highly reactive and diffusible molecule possessing minimal specificity in its interactions. The purpose of this short review is to revisit some of the 'controversial' aspects of NO-mediated regulation of myocardial function, taking into account our current understanding of how mammalian cells may target and regulate the synthesis of NO in such a way that NO can serve diverse physiological functions.

NOVELNEURALMODULATORS

The discovery that nitric oxide (NO) is produced by neurons and regulates synaptic activity has challenged the definition of a neurotransmitter. NO is not stored in synaptic vesicles and does not act at conventional receptors on the surface of adjacent neurons. The toxic gases carbon monoxide (CO) and hydrogen sulfide (H2S) are also produced by neurons and modulate synaptic activity. D-serine synthesis and release by astrocytes as an endogenous ligand for the "glycine" site of N-methyl D-aspartate (NMDA) receptors defy the concept that a neurotransmitter must be synthesized by neurons. We review the properties of these "atypical" neural modulators.

Early neuroprotective effect of nitric oxide in developing rat brain irradiated in utero

Pregnant Wistar rats were exposed on day 17 of gestation to 1 Gy gamma irradiation from a Co(60) source. Even though it is established that gamma radiation-dependent damage is mainly due to free radical generation neither the ascorbyl radical/ascorbate ratio nor the lipid radical content in developing rat brain were affected by prenatal irradiation. A distinctive EPR signal for the adduct NO-Fe-MGD (g=2.03 and a(N)=12.5 G) was detected in brain homogenates prepared from irradiated rats. Nitric oxide (NO)-dependent EPR signal increased in a time-dependent manner up to 2h post-irradiation. NO concentration in unirradiated brains was 37+/-4 pmol/g brain and 45+/-2, 77+/-5 and 216+/-6 after 30, 60 and 120 min post-irradiation, respectively. Total nitric oxide synthase activity was increased by 77 and 51% after 30 and 60 min post-irradiation, respectively, and returned to control values after 120 min. Thus, increased NO steady-state concentration could be ascribed to an increase in NOS activity. Taken as a whole, these results suggest that NO might act to protect the developing brain from the cytotoxicity of reactive species.

Characterization and function of mitochondrial nitric-oxide synthase

The mitochondrial production of nitric oxide is catalyzed by a nitric-oxide synthase. This enzyme has the same cofactor and substrate requirements as other constitutive nitric-oxide synthases. Its occurrence was demonstrated in various mitochondrial preparations (intact, purified mitochondria, permeabilized mitochondria, mitoplasts, submitochondrial particles) from different organs (liver, heart) and species (rat, pig). Endogenous nitric oxide reversibly inhibits oxygen consumption and ATP synthesis by competitive inhibition of cytochrome oxidase. The increased K(m) of cytochrome oxidase for oxygen and the steady-state reduction of the electron chain carriers provided experimental evidence for the direct interaction of this oxidase with endogenous nitric oxide. The increase in hydrogen peroxide production by nitric oxide-producing mitochondria not accompanied by the full reduction of the respiratory chain components indicated that cytochrome c oxidase utilizes nitric oxide as an alternative substrate. Finally, effectors or modulators of cytochrome oxidase (the irreversible step in oxidative phosphorylation) had been proposed during the last 40 years. Nitric oxide is the first molecule that fulfills this role (it is a competitive inhibitor, produced at a fair rate near the target site) extending the oxygen gradient to tissues.

Nitrosopeptide mapping: a novel methodology reveals s-nitrosylation of dexras1 on a single cysteine residue

S-Nitrosylation of specific cysteine residues is a reversible signaling mechanism of nitric oxide (NO) generated by NO synthase (NOS) enzymes. In some proteins, evidence has accumulated that more than one cysteine can be S-nitrosylated; however, it is difficult to distinguish S-nitrosylation on separate cysteine residues. We report a novel simple, sensitive, and specific procedure for nitrosopeptide mapping. Dexras1 is a monomeric G protein whose guanine nucleotide exchange activity is augmented by NO; the identity and number of its S-nitrosylated cysteines is unknown. We describe the radiolabeling of S-nitrosylated cysteine residues in Dexras1. A nitrosopeptide map, generated by two-dimensional peptide chromatography, reveals that only a single cysteine is S-nitrosylated following NO exposure. Mutagenesis of Cys11 abolished the effect of NO donors on Dexras1, implicating this residue in the NO-mediated activation of Dexras1.

Nitric oxide signalling in salivary glands

Nitric oxide (NO) plays multiple roles in both intracellular and extracellular signalling mechanisms with implications for health and disease. This review focuses on the role of NO signalling in salivary secretion. Attention will be paid primarily to endogenous NO production in acinar cells resulting from specific receptor stimulation and to NO-regulated Ca2+ homeostasis. Due to the fact that NO readily crosses membranes by simple diffusion, endogenous NO may play a physiological role in processes as diverse as modifying the secretory output, controlling blood supply to the gland, modulating transmitter output from nerve endings, participating in the host defence barrier, and affecting growth and differentiation of surrounding tissue. Furthermore, the role of NO in the pathogenesis of human oral diseases will be considered.

Biochemistry of mitochondrial nitric-oxide synthase

We reported that the generation of nitric oxide by mitochondria is catalyzed by a constitutive, mitochondrial nitric-oxide synthase (mtNOS). Given that this production may establish the basis for a novel regulatory pathway of energy metabolism, oxygen consumption, and oxygen free radical production, it becomes imperative to identify unequivocally and characterize this enzyme to provide a basis for its regulation. The mitochondrial localization of mtNOS was supported by following the hepatic distribution of mtNOS, immunoblotting submitochondrial fractions, and immunohistochemistry of liver tissues. mtNOS was identified as brain NOS alpha by various methods (mass spectrometry of proteolytic fragments, amino acid analysis, molecular weight, pI, and analysis of PCR fragments), excluding the occurrence of a novel isoform or other splice variants. Distribution of mtNOS transcript indicated its occurrence in liver, brain, heart, muscle, kidney, lung, testis, and spleen. In contrast to brain NOS, mtNOS has two post-translational modifications: acylation with myristic acid and phosphorylation at the C terminus. The former modification is a reversible and post-translational process, which may serve for subcellular targeting or membrane anchoring. The latter modification could be linked to enzymatic regulation. These results are discussed in terms of the role that nitric oxide may have in cellular bioenergetics.

PKC-zeta prevents oxidant-induced iNOS upregulation and protects the microtubules and gut barrier integrity

Using intestinal (Caco-2) monolayers, we reported that inducible nitric oxide synthase (iNOS) activation is key to oxidant-induced barrier disruption and that EGF protects against this injury. PKC-zeta was required for protection. We thus hypothesized that PKC-zeta activation and iNOS inactivation are key in EGF protection. Wild-type (WT) Caco-2 cells were exposed to H(2)O(2) (0.5 mM) +/- EGF or PKC modulators. Other cells were transfected to overexpress PKC-zeta or to inhibit it and then pretreated with EGF or a PKC activator (OAG) before oxidant. Relative to WT cells exposed to oxidant, pretreatment with EGF protected monolayers by 1) increasing PKC-zeta activity; 2) decreasing iNOS activity and protein, NO levels, oxidative stress, tubulin oxidation, and nitration); 3) increasing polymerized tubulin; 4) maintaining the cytoarchitecture of microtubules; and 5) enhancing barrier integrity. Relative to WT cells exposed to oxidant, transfected cells overexpressing PKC-zeta (+2.9-fold) were protected as indicated by decreases in all measures of iNOS-driven pathways and enhanced stability of microtubules and barrier function. Overexpression-induced inhibition of iNOS was OAG independent, but EGF potentiated this protection. Antisense inhibition of PKC-zeta (-95%) prevented all measures of EGF protection against iNOS upregulation. Thus EGF protects against oxidative disruption of the intestinal barrier by stabilizing the cytoskeleton in large part through the activation of PKC-zeta and downregulation of iNOS. Activation of PKC-zeta is by itself required for cellular protection against oxidative stress of iNOS. We have thus discovered novel biologic functions, suppression of the iNOS-driven reactions and cytoskeletal oxidation, among the atypical PKC isoforms.

Role of nitric oxide synthase against MPTP neurotoxicity in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic pathway injury similar to that observed in Parkinson's disease. Many hypotheses have been proposed to explain the mechanisms underlying MPTP neurotoxicity. Previous work showed that the inhibitor of neuronal nitric oxide synthase (nNOS) might produce protection against MPTP-induced dopaminergic toxicity. To exactly test the role of NO in MPTP neurotoxicity, we examined the effect of nNOS inhibitor 7-nitroindazole, in comparison with that of nonselective NOS inhibitor (L-NAME), immunosuppressant (FK-506), monoamine oxidase (MAO) inhibitors (clorgyline and pargyline), N-methyl-D-aspartate receptor antagonist (MK-801) and Ca2+ antagonist (amlodipine). Among seven compounds, 7-nitroindazole produced dose-dependent protection against MPTP-induced depletion of striatal dopamine and its metabolite 3,4-dihydroxyphenyl acetic acid (DOPAC) in mice. Clorgyline and pargyline also showed a significant effect on MPTP-induced dopamine depletion in the mouse striatum. However, both compounds did not protect against MPTP-induced depletion of striatal DOPAC Our immunohistological study with tyrosine hydroxylase (TH) and microtuble-associated protein 2 (MAP 2) showed that 7-nitroindazole or pargyline can protect against MPTP-induced depletion of TH and MAP 2 immunostained neurons in the substantia nigra. Furthermore, these compounds reduced a marked increase in GFAP-positive astrocytes of the mouse striatum after MPTP treatments. The present study demonstrates that nNOS inhibitor 7-nitroindazole as well as MAO inhibitors clorgyline and pargyline can produce dose-dependent neuroprotection against the dopaminergic neurotoxicity of MPTP. However, nonselective NOS inhibitor L-NAME, immunosuppressant FK-506, NMDA receptor antagonist MK-801 and Ca2+ antagonist amlodipine did not show a beneficial effect on MPTP neurotoxicity.