Nitric oxide modulates Na+, K+-ATPase activity through cyclic GMP pathway in proximal rat trachea

Nitric oxide donating anti-glaucoma drugs: advances and prospects

Glaucoma is a disease that causes irreversible blindness. Reducing intraocular pressure (IOP) is the main treatment at present. Nitric oxide (NO), an endogenous gas signaling molecule, can increase aqueous humor outflow facility, inhibit aqueous humor production thereby reducing IOP, as well as regulate eye blood flow and protect the optic nerve. Therefore, NO donating anti-glaucoma drugs have broad research prospects. In this review, we summarize NO-mediated therapy for glaucoma, and the state of the art of some NO donating molecules, including latanoprostene bunod in market and some other candidate compounds, for the intervention of glaucoma, as well as prospects and challenges ahead in this field.

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

eNOS Gene Affects Red Cell Deformability: Role of T-786C, G894T, and 4a/4b Polymorphisms

Plasma viscosity and erythrocyte deformability play a key role in maintaining and regulating microcirculation. In vitro and in vivo studies suggested a role for nitric oxide (NO) in modulating flow-mediated vasodilatation and red blood cell deformability. Impaired NO availability due to mutations in eNOS gene might contribute to the altered haemorheologic state. The aim of this study was to investigate the role of eNOS T-786C, G894T, and 4a/4b polymorphisms in modulating the haemorheologic state in a clinical condition characterized by a microcirculatory disorder. Eighty patients with idiopathic sudden sensorineural hearing loss (ISSHL) and 80 healthy subjects were studied. By using a dominant model of inheritance, we found a significant association between eNOS 894T rare variant and ISSHL (odds ratio [OR] 894TT+GT = 2.08, p = 0.03) after adjustment with traditional vascular risk factors. A higher percentage of altered red cell deformability both in patients and in controls carrying the eNOS rare variants was found in comparison to subjects carrying the wild type. Apart from the disease, eNOS T-786C and G894T polymorphisms independently affected the deformability index (OR,-786CC+TC = 2.81, p = 0.01 and OR, 894TT+GT = 2.5, p = 0.02, respectively), in particular in subjects in whom the contemporary presence of the two rare alleles was observed (OR,-786CC+TC and 894TT+GT combined genotype = 6.9, p<0.0001). Our study documented that eNOS gene affects the red blood cell deformability, so possibly contributing to ISSHL, which may represent a suitable model of microcirculatory disorder.

The Influence of Na(+), K(+)-ATPase on Glutamate Signaling in Neurodegenerative Diseases and Senescence

Decreased Na(+), K(+)-ATPase (NKA) activity causes energy deficiency, which is commonly observed in neurodegenerative diseases. The NKA is constituted of three subunits: α, β, and γ, with four distinct isoforms of the catalytic α subunit (α1-4). Genetic mutations in the ATP1A2 gene and ATP1A3 gene, encoding the α2 and α3 subunit isoforms, respectively can cause distinct neurological disorders, concurrent to impaired NKA activity. Within the central nervous system (CNS), the α2 isoform is expressed mostly in glial cells and the α3 isoform is neuron-specific. Mutations in ATP1A2 gene can result in familial hemiplegic migraine (FHM2), while mutations in the ATP1A3 gene can cause Rapid-onset dystonia-Parkinsonism (RDP) and alternating hemiplegia of childhood (AHC), as well as the cerebellar ataxia, areflexia, pescavus, optic atrophy and sensorineural hearing loss (CAPOS) syndrome. Data indicates that the central glutamatergic system is affected by mutations in the α2 isoform, however further investigations are required to establish a connection to mutations in the α3 isoform, especially given the diagnostic confusion and overlap with glutamate transporter disease. The age-related decline in brain α2∕3 activity may arise from changes in the cyclic guanosine monophosphate (cGMP) and cGMP-dependent protein kinase (PKG) pathway. Glutamate, through nitric oxide synthase (NOS), cGMP and PKG, stimulates brain α2∕3 activity, with the glutamatergic N-methyl-D-aspartate (NMDA) receptor cascade able to drive an adaptive, neuroprotective response to inflammatory and challenging stimuli, including amyloid-β. Here we review the NKA, both as an ion pump as well as a receptor that interacts with NMDA, including the role of NKA subunits mutations. Failure of the NKA-associated adaptive response mechanisms may render neurons more susceptible to degeneration over the course of aging.

Nitric oxide regulation of Na, K-ATPase activity in ocular ciliary epithelium involves Src family kinase

The nitric oxide (NO) donor sodium nitroprusside (SNP) is known to reduce aqueous humor (AH) secretion in the isolated porcine eye. Previously, SNP was found to inhibit Na,K-ATPase activity in nonpigmented ciliary epithelium (NPE), AH-secreting cells, through a cGMP/protein kinase G (PKG)-mediated pathway. Here we show Src family kinase (SFK) activation in the Na,K-ATPase activity response to SNP. Ouabain-sensitive (86) Rb uptake was reduced by >35% in cultured NPE cells exposed to SNP (100 µM) or exogenously added cGMP (8-Br-cGMP) (100 µM) and the SFK inhibitor PP2 (10 µM) prevented the response. Ouabain-sensitive ATP hydrolysis was reduced by ~40% in samples detected in material obtained from SNP- and 8-Br-cGMP-treated cells following homogenization, pointing to an intrinsic change of Na,K-ATPase activity. Tyrosine-10 phosphorylation of Na,K-ATPase α1 subunit was detected in SNP and L-arginine-treated cells and the response prevented by PP2. SNP elicited an increase in cell cGMP. Cells exposed to 8-Br-cGMP displayed SFK activation (phosphorylation) and inhibition of both ouabain-sensitive (86) Rb uptake and Na,K-ATPase activity that was prevented by PP2. SFK activation, which also occurred in SNP-treated cells, was suppressed by inhibitors of soluble guanylate cyclase (ODQ; 10 µM) and PKG (KT5823; 1 µM). SNP and 8-Br-cGMP also increased phosphorylation of ERK1/2 and p38 MAPK and the response prevented by PP2. However, U0126 did not prevent SNP or 8-Br-cGMP-induced inhibition of Na,K-ATPase activity. Taken together, the results suggest that NO activates guanylate cyclase to cause a rise in cGMP and subsequent PKG-dependent SFK activation. Inhibition of Na,K-ATPase activity depends on SFK activation.

Age-related changes in cerebellar phosphatase-1 reduce Na,K-ATPase activity

We evaluated whether changes in protein content and activity of PP-1 and PP-2A were the mechanism underneath the basal age-related reduction in alpha(2/3)-Na,K-ATPase activity in rats cerebella and whether this occurred through the cyclic GMP-PKG pathway. PP1 activity, but not its expression, increased with age, whereas PP-2 was not changed. The activity of alpha(2/3)-Na,K-ATPase varied with age, and there was a negative association between the PP-1 and alpha(2/3)-Na,K-ATPase activities. In young rats, the inhibition of PP-1 and PP-2A by okadaic acid (OA) increased in a dose-dependent manner alpha(1)- and alpha(2/3)-Na,K-ATPase, but had no effect on Mg-ATPase activity. A direct stimulation of PKG with 8-Br-cyclic GMP did not surmount the effect of OA. This analogue of cyclic GMP inhibited PP-1 activity only, indicating that at least part of the increase in alpha(1)- and alpha(2/3)-Na,K-ATPase activity induced by OA was mediated by the cyclic GMP-PKG-PP-1 cascade. Taking into account that PP1 inhibition increased alpha(2/3)-Na,K-ATPase activity, we propose that an age-related increase in PP-1 activity due to a decrease in cyclic GMP-PKG modulation plays a role for the age-related reduction of alpha(2/3)-Na,K-ATPase activity in rat cerebellum.

Hemorheologic profile in systemic sclerosis: role of NOS3 -786T > C and 894G >T polymorphisms in modulating both the hemorheologic parameters and the susceptibility to the disease

OBJECTIVE

Microvascular disorders are relevant in systemic sclerosis (SSc). Hyperviscosity, due to alterations of blood cells and plasma components, may play a role in the pathogenesis of microcirculatory disorders. An impaired availability of nitric oxide, related to polymorphisms in NOS3, the gene for endothelial cell nitric oxide synthase, might influence erythrocyte deformability. We undertook this study to investigate the hemorheologic profile in SSc and the role of NOS3 polymorphisms in modulating the hemorheologic status of SSc patients.

METHODS

We studied 113 consecutive SSc patients (75 with limited cutaneous SSc [lcSSc] and 38 with diffuse cutaneous SSc [dcSSc]) and 113 healthy controls. The hemorheologic profile was obtained by assessing whole blood viscosity (WBV; at shear rates of 0.512 and 94.5 seconds(-1)), plasma viscosity (PLV; at a shear rate of 94.5 seconds(-1)), and erythrocyte deformability index (DI). We determined NOS3 polymorphisms by molecular analysis.

RESULTS

A marked alteration of hemorheologic parameters was found both in patients with lcSSc and in those with dcSSc compared with controls (P < 0.0001). In multivariate analysis, rheologic variables were significantly associated with the disease (for WBV at a shear rate of 94.5 seconds(-1), odds ratio [OR] 5.4, 95% confidence interval [95% CI] 1.4-19.9, P = 0.01; for PLV, OR 2.8, 95% CI 1.2-6.5, P = 0.01; for DI, OR 3.9, 95% CI 1.4-10.8, P = 0.007), and NOS3 -786C and 894T alleles significantly affected the DI (for -786C allele, OR 2.3, 95% CI 1.01-5.4, P = 0.04; for 894T allele, OR 2.2, 95% CI 1.01-4.8, P = 0.04). The simultaneous presence of the -786C and 894T alleles represented a susceptibility factor for SSc (OR 2.8, 95% CI 1.4-5.7, P = 0.004).

CONCLUSION

Our findings document an altered rheologic profile in SSc and demonstrate a relationship between this alteration and NOS3 polymorphisms, thus shedding light on a potential novel mechanism influencing the microcirculation in this disease.

NO donors inhibit Na,K-ATPase activity by a protein kinase G-dependent mechanism in the nonpigmented ciliary epithelium of the porcine eye

1. We developed a novel method to isolate nonpigmented epithelial (NPE) cells from porcine eyes in order to examine Na,K-ATPase responses to nitric oxide (NO) donors specifically in the epithelium. 2. Cells were treated with NO donors and other test compounds for 20 min prior to Na,K-ATPase activity measurement. 3. NO donors, sodium nitroprusside (SNP, 1 microM-1 mM), sodium azide (100 nM-1 microM) and S-nitroso-N-acetylpenicillamine (1 microM-1 mM) caused significant concentration-dependent inhibition of Na,K-ATPase activity. Detection of nitrite in the medium of L-arginine and SNP-treated NPE confirmed NO generation. 4. Concentration-dependent inhibition of Na,K-ATPase was also obtained by L-arginine (1-3 mM), a physiological precursor of NO and 8p-CPT-cGMP (1-100 microM), a cell permeable analog of cGMP. The L-arginine effect was abolished when the NO synthesizing enzyme, NO-synthase, was inhibited by L-NAME (100 microM). 5. The inhibitory effect of SNP or sodium azide on Na,K-ATPase activity was suppressed by soluble guanylate cyclase (sGC) inhibitors, ODQ (10 microM) or methylene blue (10 microM). 6. The inhibitory effect of 8p-CPT-cGMP on Na,K-ATPase was abolished by protein kinase G (PKG) inhibitors, H-8 (1 microM) and H-9 (20 microM), but not by the protein kinase A (PKA) inhibitor H-89 (100 nM). H-8 and H-9 partially suppressed the inhibitory effect of SNP on Na,K-ATPase. 7. Taken together the results indicate that Na,K-ATPase inhibition response to NO donors involves activation of sGC, generation of cGMP and activation of PKG. These findings suggest that Na,K-ATPase inhibition in NPE may contribute to the ability of NO donors to reduce aqueous humor secretion.

Involvement of guanylyl cyclase, protein kinase A and Na+ K+ ATPase in relaxations of bovine isolated bronchioles induced by GEA 3175, an NO donor

The present study was designed to investigate the role of the sodium potassium adenosine triphosphatase (the Na(+)K(+) ATPase) in relaxation of bovine isolated bronchioles by a new NO donor, GEA 3175 (3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulphonyl]amino]-)hydroxide)). Bronchioles were mounted in a wire myograph for isometric tension recordings and contracted with 5-hydroxytryptamine (5-HT) or a K(+) rich solution. Concentration-dependent relaxations evoked by GEA 3175 were inhibited by ouabain or K(+) free solution. The guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 3 microM) and ouabain (10 nM) reduced GEA 3175-evoked relaxations to the same extent without any additive effect. Iberiotoxin (10 nM), an inhibitor of large conductance Ca(2+)-activated K(+) channels inhibited GEA 3175-evoked relaxations to the same extent as ouabain. Combining ouabain and iberiotoxin completely abolished GEA 3175 relaxation. An inhibitor of protein kinase G (PKG), Rp-beta-phenyl-1,N(2)-etheno-8-bromo-guanosine-3'-5'-cyclic monophosphorothioate (Rp-8-Br-PET-cGMPs), slightly reduced GEA 3175-induced relaxations. An inhibitor of cyclic AMP-dependent kinase (PKA), Rp-adenosine-3'-5'-cyclic phosphorothioate (Rp-cAMPs), inhibited the GEA 3175-induced relaxations to the same extent as ouabain. Inhibition of both PKG and PKA abolished GEA 3175 relaxation. The study provides evidence that the NO donor GEA 3175 causes guanylyl cyclase-dependent relaxations, taking place through cyclic GMP and cyclic AMP-dependent protein kinases followed by opening of large conductance Ca(2+)-activated K(+) channels and activation of smooth muscle Na(+)K(+) ATPase.

Age-related changes in cyclic GMP and PKG-stimulated cerebellar Na,K-ATPase activity

Energy deficiency and dysfunction of the Na,K-ATPase are common consequences of many pathological insults. Glutamate through cyclic GMP and cyclic GMP-dependent protein kinase (PKG) has been shown to stimulate alpha(2/3)-Na,K-ATPase activity in the central nervous system. Thus, a slight impairment of this pathway may amplify the disruption of ion homeostasis in the presence of a non-lethal insult. We investigate the effect of aging (4, 12 and 24 months) on the glutamate-cyclic GMP-PKG modulation of alpha1, alpha(2/3)-Na,K-ATPase activity in rat cerebellum and the stimulation of the glutamate-cyclic GMP-PKG pathway at different levels. Cyclic GMP levels and alpha(2/3)-Na,K-ATPase activity were progressively decreased from 4 and 24 month-old animals. However, PKG basal activity was reduced between 4 and 12 months, and no additional change was observed at 24 months. The ability of 8-Br-cyclic GMP to stimulate PKG activity was only reduced between 12 and 24 months. Moreover, glutamate or 8-Br-cyclic GMP promoted a smaller increase of alpha(2/3)-Na,K-ATPase activity at 24 months, when compared to 4 and 12 months. In spite of the age-related reduced basal levels of cyclic GMP, the production induced by CO or NO was not age-related. Finally, inhibition of PKG activation by KT5823 revealed a lower sensitivity of the enzyme at the older age. Taken together, these data show that basal age-related decline in sodium pump activity is a consequence of changes in different steps of the cyclic GMP-PKG pathway. On the other hand, age-related reduction in glutamate positive modulation of cerebellar alpha(2/3)-Na,K-ATPase is linked to a defective PKG signaling pathway.

Nitric oxide synthase in the gill of Atlantic salmon: colocalization with and inhibition of Na+,K+-ATPase

We investigated the relationship between nitric oxide (NO) and Na+,K+-ATPase (NKA) in the gill of anadromous Atlantic salmon. Cells containing NO-producing enzymes were revealed by means of nitric oxide synthase (NOS) immunocytochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry, which can be used as an indicator of NOS activity, i.e. NO production. Antibodies against the two constitutive NOS isoforms, neuronal and endothelial NOS, both produced immunoreactivity restricted to large cells at the base and along the secondary lamellae. NADPHd-positive cells showed a corresponding distribution. Antibodies against the inducible NOS isoform only labeled small cells located deep in the filament. Using in situ hybridization and NKA immunoreactivity, cells expressing Na+,K+-ATPaseα-subunit mRNA were found to have a similar distribution to the NOS cells. Double labeling for NOS immunoreactivity and NKA α-subunit mRNA revealed cellular colocalization of NKA α-subunit mRNA and nNOS protein in putative chloride cells at the base of the lamellae and interlamellar space. Along the lamellae, some NOS- or NKA-immunoreactive cells possessed a relatively lower expression of NKA α-subunit mRNA in smolts. A clear increase in NADPHd staining in the gill was demonstrated from parr to smolt. The regulatory role of NO on gill NKA activity was studied in vitrousing sodium nitroprusside (SNP; 1 mmol l-1) and PAPA-NONOate(NOC-15; 0.5 mmol l-1) as NO donors. Both SNP and NOC-15 inhibited gill NKA activity by 30% when compared to controls. The study shows that NO systems are abundant in the gill of Atlantic salmon, that NO may be produced preferentially by a constitutive NOS isoform, and suggests that NO influence on gill functions is mediated via intracellular, possibly both auto/paracrine,inhibition of Na+,K+-ATPase activity in chloride cells. Furthermore, the increase in NADPHd in the gill during smoltification suggests a regulatory role of NO in the attenuation of the smoltification-related increase in Na+,K+-ATPase activity prior to entering seawater.

Differential regulation of the release of tumor necrosis factor-alpha and of eicosanoids by mast cells in rat airways after antigen challenge

BACKGROUND: Rat trachea display a differential topographical distribution of connective tissue mast cells (CTMC) and mucosal mast cells (MMC) that may imply regional differences in the release of allergic mediators such as tumor necrosis factor-alpha (TNF-alpha) and eicosanoids. AIM: To evaluate the role of CTMC and MMC for release of TNF-alpha and eicosanoids after allergenic challenge in distinct segments of rat trachea. MATERIALS AND METHODS: Proximal trachea (PT) and distal trachea (DT) from ovalbumin (OVA)-sensitized rats, treated or not with compound 48/80 (48/80) or dexamethasone, were incubated in culture medium. After OVA challenge, aliquots were collected to study release of TNF-alpha and eicosanoids. RESULTS: Release of TNF-alpha by PT upon OVA challenge peaked at 90 min and decayed at 6 and 24 h. Release from DT peaked at 30-90 min and decayed 6 and 24 h later. When CTMC were depleted with 48/80, OVA challenge exacerbated the TNF-alpha release by PT at all time intervals, while DT exacerbated TNF-alpha levels 6 and 24 h later only. Dexamethasone reduced TNF-alpha production after 90 min of OVA challenge in PT and at 3 and 6h in DT. OVA challenge increased prostaglandin D2) in DT and leukotriene B4 in both segments but did not modify prostaglandin E2 and leukotriene C4 release. CONCLUSION: OVA challenge induces TNF-alpha release from MMC, which is negatively regulated by CTMC. The profile of TNF-alpha and eicosanoids depends on the time after OVA challenge and of the tracheal segment considered.

Guanylyl cyclases, nitric oxide, natriuretic peptides, and airway smooth muscle function

Airway smooth muscle (ASM) plays an important role in asthma pathophysiology through its contractile and proliferative functions. The cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) are second messengers capable of mediating the effects of a variety of drugs and hormones. There is a large body of evidence to support the hypothesis that cAMP is a mediator of the ASM's relaxant effects of drugs, such as beta2-adrenoceptor agonists, in human airways. Although most attention has been paid to this second messenger and the signal transduction pathways it activates, recent evidence suggests that cGMP is also an important second messenger in ASM with important relaxant and antiproliferative effects. Here, we review the regulation and function of cGMP in ASM and discuss the implications for asthma pathophysiology and therapeutics. Recent studies suggest that activators of soluble and particulate guanylyl cyclases, such as nitric oxide donors and natriuretic peptides, have both relaxant and antiproliferative effects that are mediated through cGMP-dependent and cGMP-independent pathways. Abnormalities in these pathways may contribute to asthma pathophysiology, and therapeutic manipulation may complement the effects of beta2-adrenoceptor agonists.

Regulation of Na+/K+-ATPase activity by nitric oxide in the kidney and gill of the brown trout (Salmo trutta)

In teleost fish, successful osmoregulation involves controlled ion transport mechanisms in kidney and gill epithelia. In this study, the effect of nitric oxide (NO) on Na(+)/K(+)-ATPase was investigated in vitro in these two tissues in brown trout (Salmo trutta) acclimated to freshwater. The NO donor sodium nitroprusside (SNP) inhibited in situ Na(+)/K(+)-ATPase activity, measured as ouabain-sensitive Rb(+) uptake, in both samples of kidney and gill tissue and in isolated gill cells. The effect was dose-dependent in both tissues, with a maximal observed inhibition of approximately 40-50% (1 mmol l (-1) SNP). The time-course of inhibition revealed a maximum effect with 10 min pre-incubation. The effect of SNP was reproduced with another NO donor, papa-nonoate (NOC-15; 200 micro mol l(-1)), and was prevented by the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; 1 mmol l(-1)). To further investigate the mechanism of the NO effect, whole-tissue Na(+) and K(+) levels were analysed. In kidney, SNP (1 mmol l(-1)) led to an increase in tissue Na(+) levels and a decrease in K(+) levels in a 3:2 ratio. In gill tissue, no change in either ion was observed. These observations indicate that the effect on Na(+)/K(+)-ATPase is direct rather than due to a decrease in intracellular Na(+), its rate-limiting substrate. SNP elevated the level of cyclic GMP (cGMP) in both kidney and gill tissue. Dibutyryl cyclic GMP (db-cGMP; 1 mmol l(-1)) also inhibited Na(+)/K(+)-ATPase activity in both tissues. Hence, a possible mechanism may involve the cGMP-activated kinase, even though other mechanisms cannot be excluded.

Effects of nitric oxide on red blood cell deformability

In addition to its known action on vascular smooth muscle, nitric oxide (NO) has been suggested to have cardiovascular effects via regulation of red blood cell (RBC) deformability. The present study was designed to further explore this possibility. Human RBCs in autologous plasma were incubated for 1 h with NO synthase (NOS) inhibitors [N(omega)-nitro-l-arginine methyl ester (l-NAME) and S-methylisothiourea], NO donors [sodium nitroprusside (SNP) and diethylenetriamine (DETA)-NONOate], an NO precursor (l-arginine), soluble guanylate cyclase inhibitors (1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one and methylene blue), and a potassium channel blocker [triethylammonium (TEA)]. After incubation, RBC deformability at various shear stresses was determined by ektacytometry. Both NOS inhibitors significantly reduced RBC deformability above a threshold concentration, whereas the NO donors increased deformability at optimal concentrations. NO donors, as well as the NO precursor l-arginine and the potassium blocker TEA, were able to reverse the effects of NOS inhibitors. Guanylate cyclase inhibition reduced RBC deformation, with both SNP and DETA-NONOate able to reverse this effect. These results thus indicate the importance of NO as a determinant of RBC mechanical behavior and suggest its regulatory role for normal RBC deformability.

Contribution of amiloride-insensitive pathways to alveolar fluid clearance in adult rats

The contributions of amiloride-sensitive and -insensitive fractions of alveolar fluid clearance in adult ventilated rats were studied under control conditions and after beta-adrenergic stimulation. Rats were instilled with a 5% albumin solution containing terbutaline (10(-4) M) or dibutyryl-cGMP (DBcGMP; 10(-4) M) with or without the cyclic nucleotide-gated cation channel inhibitor l-cis-diltiazem (10(-3) M) and/or amiloride (10(-3) M). Alveolar fluid clearance over 1 h was 18 +/- 2% in controls. In controls, amiloride inhibited 46 +/- 15% of alveolar fluid clearance, whereas l-cis-diltiazem had no inhibitory effect. Terbutaline and DBcGMP stimulated alveolar fluid clearance by 85 +/- 3 and 36 +/- 5%, respectively. Amiloride and l-cis-diltiazem inhibited nearly equal fractions of terbutaline-stimulated alveolar fluid clearance when given alone. Amiloride and l-cis-diltiazem given together inhibited a significantly larger fraction of alveolar fluid clearance in terbutaline-stimulated rats and in DBcGMP-stimulated rats. Based on these data, terbutaline stimulation recruited both amiloride-sensitive and l-cis-diltiazem-sensitive pathways. In contrast, DBcGMP mainly recruited l-cis-diltiazem-sensitive pathways. Therefore, the amiloride-insensitive fraction of Na+-driven alveolar fluid clearance may be partly mediated through cyclic nucleotide-gated cation channels and activated by an increase in intracellular cGMP.

Carbachol inhibits Na(+)-K(+)-ATPase activity in choroid plexus via stimulation of the NO/cGMP pathway

Secretion of cerebrospinal fluid by the choroid plexus can be inhibited by its cholinergic innervation. We demonstrated that carbachol inhibits the Na(+)-K(+)-ATPase in bovine choroid tissue slices and investigated the mechanism. Many of the actions of cholinergic agents are mediated by nitric oxide (NO), which plays important roles in fluid homeostasis. The inhibition of Na(+)-K(+)-ATPase was blocked by the NO synthase inhibitor [N(omega)-nitro-L-arginine methyl ester] and was quantitatively mimicked by the NO agonists sodium nitroprusside (SNP) and diethylenetriamine NO. Inhibition by SNP correlated with an increase in tissue cGMP and was abolished by 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. Inhibition was mimicked by the protein kinase G activator 8-bromo-cGMP and by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. cGMP-dependent protein kinase inhibitors Rp-8-pCPT-cGMP (0.5-5 microM) and KT-5823 (2.0 microM) did not block the effects of SNP, but higher concentrations of the more selective inhibitor (Rp-8-pCPT-cGMP) had a pharmacological inhibitory effect on Na(+)-K(+)-ATPase. The data suggest that cholinergic regulation of the Na(+)-K(+)-ATPase is mediated by NO and involves activation of guanylate cyclase and elevation of cGMP.

Review article: new insights into the pathogenesis of radiation-induced intestinal dysfunction

Exposure of the abdomino-pelvic region to ionizing radiation, such as that received during radiotherapy, is associated with the development of a number of untoward symptoms which may limit the course of therapy or which may involve serious chronic intestinal disease. While the mucosal dysfunction surrounding acute radiation enteritis is generally ascribed to the effects of ionizing radiation on the cell cycle of epithelial stem cells of the intestinal crypts and subsequent epithelial loss, recent evidence suggests that other, earlier events also play a role. The severity of these early events may determine the incidence and severity of chronic enteritis. The mechanism for this is unclear, but may relate to radiation-induced compromise of host defence responses to luminal pathogens or antigens. This review will address the current state of knowledge of the pathogenesis of radiation-induced intestinal dysfunction, focusing on events which occur in the mucosa, and will discuss what the future may hold with respect to the treatment of radiation-associated diseases of the intestinal tract.

Influence of age on nitric oxide modulatory action on Na(+), K(+)-ATPase activity through cyclic GMP pathway in proximal rat trachea

Age-related changes in the modulatory action of nitric oxide (NO) on cyclic GMP levels and Na(+),K(+)-ATPase activity in the proximal rat trachea were investigated using sodium nitroprusside, 8-bromo-cyclic GMP and okadaic acid. At 24 months, both control activities of Na(+), K(+)-ATPase and Mg(2+)-ATPase were decreased when compared to the segments from 4- and 12-month-old animals. However, cyclic GMP levels were similar among the three ages. Sodium nitroprusside (100 microM) induced stimulation of Na(+),K(+)-ATPase activity in segments from both 4- and 12-month-old animals, but not 24-month-old animals. The effect was specific for Na(+),K(+)-ATPase since Mg(2+)-ATPase activity was unaffected. Sodium nitroprusside induced an increase in nitrates/nitrites and cyclic GMP levels in proximal segments at 4, 12 and 24 months. The 8-bromo-cyclic GMP (100 microM) induced a similar specific stimulation of Na(+),K(+)-ATPase activity in segments from 4- and 12- but not 24-month-old animals. Okadaic acid (1 microM), a phosphatase-1 inhibitor, increased proximal Na(+), K(+)-ATPase but not Mg(2+)-ATPase activity in tissues from 4-, 12- and 24-month-old animals. Our results suggest that aging affects cyclic GMP pathway in proximal rat trachea by an action at the level of the cyclic GMP-dependent protein kinase.