Sulfhydryls associated with H2O2-induced channel activation are on luminal side of ryanodine receptors

In vivo cytosolic H2O2 changes and Ca2+ homeostasis in mouse skeletal muscle

Hydrogen peroxide (H2O2) and calcium ions (Ca2+) are functional regulators of skeletal muscle contraction and metabolism. Although H2O2 is one of the activators of the type-1 ryanodine receptor (RyR1) in the Ca2+ release channel, the interdependence between H2O2 and Ca2+ dynamics remains unclear. This study tested the following hypotheses using an in vivo model of mouse tibialis anterior (TA) skeletal muscle. 1) Under resting conditions, elevated cytosolic H2O2 concentration ([H2O2]cyto) leads to a concentration-dependent increase in cytosolic Ca2+ concentration ([Ca2+]cyto) through its effect on RyR1; and 2) in hypoxia (cardiac arrest) and muscle contractions (electrical stimulation), increased [H2O2]cyto induces Ca2+ accumulation. Cytosolic H2O2 (HyPer7) and Ca2+ (Fura-2) dynamics were resolved by TA bioimaging in young C57BL/6J male mice under four conditions: 1) elevated exogenous H2O2; 2) cardiac arrest; 3) twitch (1 Hz, 60 s) contractions; and 4) tetanic (30 s) contractions. Exogenous H2O2 (0.1-100 mM) induced a concentration-dependent increase in [H2O2]cyto (+55% at 0.1 mM; +280% at 100 mM) and an increase in [Ca2+]cyto (+3% at 1.0 mM; +8% at 10 mM). This increase in [Ca2+]cyto was inhibited by pharmacological inhibition of RyR1 by dantrolene. Cardiac arrest-induced hypoxia increased [H2O2]cyto (+33%) and [Ca2+]cyto (+20%) 50 min postcardiac arrest. Compared with the exogenous 1.0 mM H2O2 condition, [H2O2]cyto after tetanic muscle contractions rose less than one-tenth as much, whereas [Ca2+]cyto was 4.7-fold higher. In conclusion, substantial increases in [H2O2]cyto levels evoke only modest Ca2+ accumulation via their effect on the sarcoplasmic reticulum RyR1. On the other hand, contrary to hypoxia secondary to cardiac arrest, increases in [H2O2]cyto from muscle contractions are small, indicating that H2O2 generation is unlikely to be a primary factor driving the significant Ca2+ accumulation after, especially tetanic, muscle contractions.NEW & NOTEWORTHY We developed an in vivo mouse myocyte H2O2 imaging model during exogenous H2O2 loading, ischemic hypoxia induced by cardiac arrest, and muscle contractions. In this study, the interrelationship between cytosolic H2O2 levels and Ca2+ homeostasis during muscle contraction and hypoxic conditions was revealed. These results contribute to the elucidation of the mechanisms of muscle fatigue and exercise adaptation.

Long-Term High Salt Intake Involves Reduced SK Currents and Increased Excitability of PVN Neurons with Projections to the Rostral Ventrolateral Medulla in Rats

Evidence indicates that high salt (HS) intake activates presympathetic paraventricular nucleus (PVN) neurons, which contributes to sympathoexcitation of salt-sensitive hypertension. The present study determined whether 5 weeks of HS (2% NaCl) intake alters the small conductance Ca²⁺-activated potassium channel (SK) current in presympathetic PVN neurons and whether this change affects the neuronal excitability. In whole-cell voltage-clamp recordings, HS-treated rats had significantly decreased SK currents compared to rats with normal salt (NS, 0.4% NaCl) intake in PVN neurons. The sensitivity of PVN neuronal excitability in response to current injections was greater in HS group compared to NS controls. The SK channel blocker apamin augmented the neuronal excitability in both groups but had less effect on the sensitivity of the neuronal excitability in HS group compared to NS controls. In the HS group, the interspike interval (ISI) was significantly shorter than that in NS controls. Apamin significantly shortened the ISI in NS controls but had less effect in the HS group. This data suggests that HS intake reduces SK currents, which contributes to increased PVN neuronal excitability at least in part through a decrease in spike frequency adaptation and may be a precursor to the development of salt-sensitive hypertension.

On-Demand Targeting: Investigating Biology with Proximity-Directed Chemistry

Proximity enhancement is a central chemical tenet underpinning an exciting suite of small-molecule toolsets that have allowed us to unravel many biological complexities. The leitmotif of this opus is "tethering"-a strategy in which a multifunctional small molecule serves as a template to bring proteins/biomolecules together. Scaffolding approaches have been powerfully applied to control diverse biological outcomes such as protein-protein association, protein stability, activity, and improve imaging capabilities. A new twist on this strategy has recently appeared, in which the small-molecule probe is engineered to unleash controlled amounts of reactive chemical signals within the microenvironment of a target protein. Modification of a specific target elicits a precisely timed and spatially controlled gain-of-function (or dominant loss-of-function) signaling response. Presented herein is a unique personal outlook conceptualizing the powerful proximity-enhanced chemical biology toolsets into two paradigms: "multifunctional scaffolding" versus "on-demand targeting". By addressing the latest advances and challenges in the established yet constantly evolving multifunctional scaffolding strategies as well as in the emerging on-demand precision targeting (and related) systems, this Perspective is aimed at choosing when it is best to employ each of the two strategies, with an emphasis toward further promoting novel applications and discoveries stemming from these innovative chemical biology platforms.

Acute heart failure: patient characteristics and pathophysiology

The number of hospitalizations for acute heart failure (HF) continues to increase and it remains the most common discharge diagnosis among Medicare beneficiaries. Prognosis after hospitalization for HF is poor, with high in-hospital mortality and even higher post-discharge mortality and rehospitalization rates. It is a complex clinical syndrome that varies widely with respect to clinical presentation and underlying pathophysiology. This paper reviews what is documented in the literature regarding the known pathophysiologic mechanisms reported in patients hospitalized for HF.

Antihypertensive and antioxidant potential of vanillic acid, a phenolic compound in L-NAME-induced hypertensive rats: a dose-dependence study

We investigated the antihypertensive and antioxidant potential of vanillic acid (VA) in N(ω)-Nitro-L-arginine methyl ester hydrochloride (L-NAME) - treated adult male albino Wistar rats. Treatment of rats with L-NAME (40 mg/kg Bw for 30 days) caused a sustained increase in systolic- (SBP) and diastolic blood pressure (DBP) and significantly decreased the concentration of nitrite/nitrate (NO(x)) in plasma as compared with that in the control. Rats treated with VA restored SBP and DBP to normal level and preserve the plasma NO metabolites concentration. Moreover, VA reduced lipid peroxidation products (thiobarbituric acid reactive substances, lipid hydroperoxides, conjugated dienes) and significantly restored enzymatic antioxidants (superoxide dismutase, catalase, and glutathione peroxidase), non-enzymatic antioxidants (vitamin C, vitamin E, and reduced glutathione) in the plasma. To assess the toxicity if any of VA treatment, hepatic and renal function markers were measured. Our results showed that the effect at a dose of 50 mg/kg Bw of VA was more pronounced than that of the other two doses, 25 and 100 mg/kg Bw. These results were supported by histopathology studies. We conclude that VA possesses an antihypertensive and antioxidant activity in L-NAME-induced hypertensive rats.

Dynamic modulation of Ca2+ sparks by mitochondrial oscillations in isolated guinea pig cardiomyocytes under oxidative stress

Local control of Ca(2+)-induced Ca(2+) release (CICR) depends on the spatial organization of L-type Ca(2+) channels and ryanodine receptors (RyR) in the dyad. Analogously, Ca(2+) uptake by mitochondria is facilitated by their close proximity to the Ca(2+) release sites, a process required for stimulating oxidative phosphorylation during changes in work. Mitochondrial feedback on CICR is less well understood. Since mitochondria are a primary source of reactive oxygen species (ROS), they could potentially influence the cytosolic redox state, in turn altering RyR open probability. We have shown that self-sustained oscillations in mitochondrial inner membrane potential (ΔΨ(m)), NADH, ROS, and reduced glutathione (GSH) can be triggered by a laser flash in cardiomyocytes. Here, we employ this method to directly examine how acute changes in energy state dynamically influence resting Ca(2+) spark occurrence and properties. Two-photon laser scanning microscopy was used to monitor cytosolic Ca(2+) (or ROS), ΔΨ(m), and NADH (or GSH) simultaneously in isolated guinea pig cardiomyocytes. Resting Ca(2+) spark frequency increased with each ΔΨ(m) depolarization and decreased with ΔΨ(m) repolarization without affecting Ca(2+) spark amplitude or time-to-peak. Stabilization of mitochondrial energetics by pretreatment with the superoxide scavenger TMPyP, or by acute addition of 4'-chlorodiazepam, a mitochondrial benzodiazepine receptor antagonist that blocks the inner membrane anion channel, prevented or reversed, respectively, the increased spark frequency. Cyclosporine A did not block the ΔΨ(m) oscillations or prevent Ca(2+) spark modulation by ΔΨ(m). The results support the hypothesis that mitochondria exert an influential role on the redox environment of the Ca(2+) handling subsystem, with mechanistic implications for the pathophysiology of cardiac disease.

Dietary salt activates an endothelial proline-rich tyrosine kinase 2/c-Src/phosphatidylinositol 3-kinase complex to promote endothelial nitric oxide synthase phosphorylation

Although many laboratories have shown that dietary NaCl (salt) intake increases NO production in rodents and humans, the mechanism has not been uncovered. In the present study, pharmacological and dominant-negative strategies were used to show that feeding a formulated diet containing increased amounts of salt to young male Sprague-Dawley rats induced the formation of an endothelial cell-signaling complex that contained proline-rich tyrosine kinase 2, c-Src (also known as pp60(c-src)), and phosphatidylinositol 3-kinase. In the setting of a high-salt diet, proline-rich tyrosine kinase 2 served as the scaffold for c-Src-mediated phosphatidylinositol 3-kinase activation. Phosphatidylinositol 3-kinase was the upstream activator of protein kinase B (Akt), which was responsible for phosphorylation of the rat endothelial isoform of NO synthase at S1176 and thereby promoted the increase in NO production. The combined findings illustrated the crucial role for a proline-rich tyrosine kinase 2-signaling complex in the endothelial response to salt intake.

Redox regulation of the ryanodine receptor/calcium release channel

The RyR (ryanodine receptor)/calcium release channel contains a number of highly reactive thiol groups that endow it with redox sensitivity. In general, oxidizing conditions favour channel opening, while reducing conditions have the opposite effect. Thiol modification affects the channel sensitivity to its principal effectors, Ca2+, Mg2+ and ATP, and alters RyR protein interactions. Here, we give a brief account of the major findings and prevailing views in the field.

Redox sensitivity of the ryanodine receptor interaction with FK506-binding protein

The ryanodine receptor (RyR) calcium release channel functions as a redox sensor that is sensitive to channel modulators. The FK506-binding protein (FKBP) is an important regulator of channel activity, and disruption of the RyR2-FKBP12.6 association has been implicated in cardiac disease. In the present study, we investigated whether the RyR-FKBP association is redox-regulated. Using co-immunoprecipitation assays of solubilized native RyR2 from cardiac muscle sarcoplasmic reticulum (SR) with recombinant [(35)S]FKBP12.6, we found that the sulfydryl-oxidizing agents, H(2)O(2) and diamide, result in diminished RyR2-FKBP12.6 binding. Co-sedimentation experiments of cardiac SR vesicles with [(35)S]FKBP12.6 also demonstrated that oxidizing reagents decreased FKBP binding. Matching results were obtained with skeletal muscle SR. Notably, H(2)O(2) and diamide differentially affected the RyR2-FKBP12.6 interaction, decreasing binding to approximately 75 and approximately 50% of control, respectively. In addition, the effect of H(2)O(2) was negligible when the channel was in its closed state or when applied after FKBP binding had occurred, whereas diamide was always effective. A cysteine-null mutant FKBP12.6 retained redox-sensitive interaction with RyR2, suggesting that the effect of the redox reagents is exclusively via sites on the ryanodine receptor. K201 (or JTV519), a drug that has been proposed to prevent FKBP12.6 dissociation from the RyR2 channel complex, did not restore normal FKBP binding under oxidizing conditions. Our results indicate that the redox state of the RyR is intimately connected with FKBP binding affinity.

Involvement of ryanodine-operated channels in tert-butylhydroperoxide-evoked Ca2+ mobilisation in pancreatic acinar cells

Reactive oxygen species and related oxidative damage have been implicated in the initiation of acute pancreatitis, a disease characterised in its earliest stages by disruption of intracellular Ca2+ homeostasis. The present study was carried out in order to establish the effect of the organic pro-oxidant, tert-butylhydroperoxide (tBHP), on the mobilisation of intracellular Ca2+ stores in isolated rat pancreatic acinar cells and the mechanisms underlying this effect. Cytosolic free Ca2+ concentrations ([Ca2+]c) were monitored using a digital microspectrofluorimetric system in fura-2 loaded cells. In the presence of normal extracellular Ca2+ concentrations ([Ca2+]o), perfusion of pancreatic acinar cells with 1 mmol l-1 tBHP caused a slow sustained increase in [Ca2+]c. This increase was also observed in a nominally Ca2+-free medium, indicating a release of Ca2+ from intracellular stores. Pretreatment of cells with tBHP abolished the typical Ca2+ response of both the physiological agonist CCK-8 (1 nmol l-1) and thapsigargin (TPS, 1 micromol l-1), an inhibitor of the SERCA pump, in the absence of extracellular Ca2+. Similar results were observed with carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP, 0.5 micromol l-1), a mitochondrial uncoupler. In addition, depletion of either agonist-sensitive Ca2+ pools by CCK-8 or TPS or mitochondrial Ca2+ pools by FCCP were unable to prevent the tBHP-induced Ca2+ release. By contrast, simultaneous administration of TPS and FCCP clearly abolished the tBHP-induced Ca2+ release. These results show that tBHP releases Ca2+ from agonist-sensitive intracellular stores and from mitochondria. On the other hand, simultaneous application of FCCP and of 2-aminoethoxydiphenylborane (2-APB), a blocker of IP3-mediated Ca2+ release, was unable to suppress the increase in [Ca2+]c induced by tBHP, while the application of 50 micromol l-1 of ryanodine (which is able to block the ryanodine channels) inhibits tBHP-evoked Ca2+ mobilisation. These findings indicate that tBHP releases Ca2+ from non-mitochondrial Ca2+ pools through ryanodine channels.

Molecular nature of sulfhydryl modification by hydrogen peroxide on type 1 ryanodine receptor

AIM

To elucidate the molecular nature of sulfhydryl modification by hydrogen peroxide on type 1 ryanodine receptor (RyR1).

METHODS

Rabbit skeletal muscle sarcoplasmic reticulum was treated with hydrogen peroxide, then RyR1 complex was isolated. The proteins in the complex were analysed by electrophoresis, Western blot and electron microscopy.

RESULTS

(1) Hydrogen peroxide induces inter-subunit cross-linking within the tetrameric RyR1 molecule; (2) in parallel to inter-subunit cross-linking, the RyR1 molecule changes morphology; (3) the chemical and morphological changes are reversible: upon reduction by reducing agents, the RyR1 molecule regains its original state.

CONCLUSION

These findings suggest that the molecular mechanism of RyR1 channel activity in sarcoplasmic reticulum regulated by hydrogen peroxide is through inter-subunit cross-linking within the tetrameric RyR1 molecule, which in turn induces structural changes of RyR1.

H2O2 directly activates inositol 1,4,5-trisphosphate receptors in endothelial cells

The mechanisms of H2O2-induced Ca2+ release from intracellular stores were investigated in human umbilical vein endothelial cells. It was found that U73122, the selective inhibitor of phospholipase C, could not inhibit the H2O2-induced cytosolic Ca2+ mobilization. No elevation of inositol 1,4,5-trisphosphate (IP3) was detected in cells exposed to H2O2. By loading mag-Fura-2, a Ca2+ indicator, into intracellular store, the H2O2-induced Ca2+ release from intracellular calcium store was directly observed in the permeabilized cells in a dose-dependent manner. This release can be completely blocked by heparin, a well-known antagonist of IP3 receptor, indicating a direct activation of IP3 receptor on endoplasmic reticulum (ER) membrane by H2O2. It was also found that H2O2 could still induce a relatively small Ca2+ release from internal stores after the Ca2+-ATPase on ER membrane and the Ca2+ uptake to mitochondria were simultaneously inhibited by thapsigargin and carbonyl cyanide p-trifluoromethoxyphenyl hydrazone. The later observation suggests that a thapsigargin-insensitive non-mitochondrial intracellular Ca2+ store might be also involved in H2O2-induced Ca2+ mobilization.

Intravenous administration of activated protein C in Pseudomonas-induced lung injury: impact on lung fluid balance and the inflammatory response

Background

Acute lung injury (ALI) induces a coagulation/fibrinolysis imbalance and leads to fibrin deposition. The protein C pathway is an important regulator of the coagulation system and reduces the inflammatory response. The aim of the study was to examine the effects of recombinant human activated protein C (rhAPC) in the early phase of Pseudomonas aeruginosa (Pa)-induced lung injury.

Methods

The study was conducted in vivo on a rat model of Pa-induced ALI. Continuous intravenous (IV) rhAPC was administrated simultaneously with intratracheal (IT) Pa. We instilled into the airspaces a 5% bovine albumin solution with 1 μ(Ci of ¹²⁵ I-albumin and injected IV 1 μ(Ci of ¹¹¹In-albumin to measure lung liquid clearance (LLC) and endothelial injury. Cytokines levels (TNFα and IL-6) and thrombin-antithrombin (TAT) complexes were measured in blood and bronchoalveolar lavage fluid (BALF) at 4 hours. Four groups were compared: control (CTR), pneumonia (PNP) receiving IT Pa (0.5 ml/kg of 1 × 10⁹ cfu), APC: IV rhAPC (300 μg/kg/h), A-PNP: IT Pa /IV rhAPC.

Results

Alveolar-capillary permeability was increased in the PNP versus the CTR group (0.28 ± 0.08 vs. 0.03 ± 0.01, p < 0.05). IV rhAPC in Pa-induced ALI led to further injury (0.47 ± 0.17 vs. 0.28 ± 0.08, p = 0.2). The LLC was significantly decreased in the A-PNP group compared to PNP group (9.1 ± (4.3% vs. 33.4 ± 2.6%, p < 0.05). The lung wet to dry weight ratio was significantly increased in the PNP group (4.62 ± 0.31) compared to the CTR group (3.87 ± 0.22, p < 0.05). IV rhAPC administration tends to increase this parameter in Pa-induced ALI (5.80 ± 0.66, p = 0.07). These findings were associated with a loss of inflammatory response compartmentalization measured by TNFα and IL-6 systemic levels. TAT complexes in BALF were increased in the A-PNP group (23.17 ± 2.89 ng/ml) compared to the CTR group (0.92 ± 0.17 ng/ml, p < 0.05) and the PNP group (11.06 ± 2.76 ng/ml, p < 0.05).

Conclusion

rhAPC reduces LLC following Pa-induced ALI and may influence pulmonary edema formation. The early massive fibrin formation is probably beneficial in ALI limiting both the extent of injury and permeability disorders.

Dose-dependent effect of hydrogen peroxide on calcium mobilization in mouse pancreatic acinar cells

We have employed confocal laser scanning microscopy to investigate how intracellular free calcium concentration ([Ca2+]i) is influenced by hydrogen peroxide (H2O2) in collagenase-dispersed mouse pancreatic acinar cells. In the absence of extracellular calcium, treatment of cells with increasing concentrations of H2O2resulted in an increase in [Ca2+]i, indicating the release of calcium from intracellular stores. Micromolar concentrations of H2O2induced an oscillatory pattern, whereas 1 mmol H2O2/L caused a slow and sustained increase in [Ca2+]i. H2O2abolished the typical calcium release stimulated by thapsigargin or by the physiological agonist cholecystokinin octapeptide (CCK-8). Depletion of either agonist-sensitive or mitochondrial calcium pools was unable to prevent calcium release induced by 1 mmol H2O2/L, but depletion of both stores abolished it. Additionally, lower H2O2concentrations were able to release calcium only after depletion of mitochondrial calcium stores. Treatment with either the phospholipase C inhibitor U-73122 or the inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor xestospongin C did not modify calcium release from the agonist-sensitive pool induced by 100 µmol H2O2/L, suggesting the involvement of a mechanism independent of IP3 generation. In addition, H2O2reduced amylase release stimulated by CCK-8. Finally, either the H2O2-induced calcium mobilization or the inhibitory effect of H2O2on CCK-8-induced amylase secretion was abolished by dithiothreitol, a sulphydryl reducing agent. We conclude that H2O2at micromolar concentrations induces calcium release from agonist- sensitive stores, and at millimolar concentrations H2O2can also evoke calcium release from the mitochondria. The action of H2O2is mediated by oxidation of sulphydryl groups of calcium ATPases independently of IP3 generation.Key words: hydrogen peroxide, pancreatic acinar cells, intracellular calcium stores, amylase secretion.

Coagulation, inflammation, and the risk of neonatal white matter damage

Indicators of coagulation activation are sometimes increased in the blood of newborns and adults who have a systemic inflammatory response. These coagulation factors have the ability to exacerbate inflammation, which in turn can promote coagulation. Therapies directed solely at coagulation factors and therapies directed solely at inflammation factors have not proved effective in reducing mortality in adults with a systemic inflammatory response syndrome and multi-organ dysfunction (SIRS/MOD). On the other hand, the only therapy that has reduced mortality in SIRS/MOD is activated protein C, which has both anti-coagulation and anti-inflammatory effects. This and other observations support the view that activated coagulation factors enhance inflammation. Since newborns at risk of cerebral white matter damage and cerebral palsy are more likely than their peers to have a systemic inflammatory response, which is sometimes accompanied by elevated blood levels of coagulation factors, we suggest that activated coagulation factors contribute to the occurrence of cerebral white matter damage by exacerbating inflammatory phenomena, rather than by occluding cerebral blood vessels.

Salt intake, endothelial cell signaling, and progression of kidney disease

It has been known for decades that increased dietary intake of salt (NaCl) shortens the life span of rats in a dose-dependent fashion. This review focuses specifically on the recently described biological effect and consequences of increased salt ingestion on the endothelium through a mechanism that is independent of blood pressure. Changes in salt intake are recognized by endothelial cells in the vascular tree and glomeruli through a physical process that promotes a series of signaling events involved in transcriptional regulation of genes that include transforming growth factor-beta1 (TGF-beta1) and the endothelial isoform of nitric oxide synthase (NOS3). A balance is struck between TGF-beta1 and NOS3 as salt intake varies and creates a negative feedback loop, because TGF-beta1 increased expression of NOS3 and NO inhibited production of TGF-beta1 in healthy rats. Changes in this feedback system have been observed in salt-sensitive hypertension and appear to impact end-organ damage, particularly the kidney. The data support an important benefit to reduction of salt intake in the setting of chronic kidney disease.

Acetaldehyde alters Ca2+-release channel gating and muscle contraction in a dose-dependent manner

We studied whether acetaldehyde, which is produced by alcohol consumption, impacts ryanodine receptor (RyR) activity and muscle force. Exposure to approximately 50-200 microM acetaldehyde enhanced channel activity of frog RyR and rabbit RyR1 incorporated into lipid bilayers. An increase in acetaldehyde to 1 mM modified channel activity in a time-dependent manner, with a brief activation and then inhibition. Application of 200 microM acetaldehyde to frog fibers increased twitch tension. The maximum rate of rise of tetanus tension was accelerated to 1.5 and 1.74 times the control rate on exposure of fibers to 50 and 200 microM acetaldehyde, respectively. Fluorescence monitoring with fluo 3 demonstrated that 200-400 microM acetaldehyde induced Ca(2+) release from the sarcoplasmic reticulum (SR) in frog muscles. Acetaldehyde at 1 mM inhibited twitch tension by approximately 12%, with an increased relaxation time after a small, transient twitch potentiation. These results suggest that moderate concentrations of acetaldehyde can elicit Ca(2+) release from the SR by increasing the open probability of the RyR channel, resulting in increased tension. However, the effects of acetaldehyde at clinical doses (1-30 microM) are unlikely to mediate alcohol-induced acute muscle dysfunction.

Mechanisms responsible for catalysis of the inhibition of factor Xa or thrombin by antithrombin using a covalent antithrombin-heparin complex

Covalent antithrombin-heparin (ATH) complexes, formed spontaneously between antithrombin (AT) and unfractionated standard heparin (H), have a potent ability to catalyze the inhibition of factor Xa (or thrombin) by added AT. Although approximately 30% of ATH molecules contain two AT-binding sites on their heparin chains, the secondary site does not solely account for the increased activity of ATH. We studied the possibility that all pentasaccharide AT-binding sequences in ATH may catalyze factor Xa inhibition. Chromatography of ATH on Sepharose-AT resulted in >80% binding of the load. Similar chromatographies of non-covalent AT + H mixtures lead to a lack of binding for AT and fractionation of H into unbound (separate from AT) or bound material. Gradient elution of ATH from Sepharose-AT gave 2 peaks, a peak containing higher affinity material that had greater anti-factor Xa catalytic activity (708 units/mg heparin) compared with the peak containing lower affinity material (112 units/mg). Sepharose-AT chromatography of the ATH component with short heparin chains (<or=12 monosaccharides) resulted in active unbound (40%) and bound fractions (190 and 560 units/mg, respectively). Factor Xa-ATH or thrombin-ATH inhibitor complexes gave chromatograms on Sepharose-AT with more unbound material compared with that of free ATH. Also, ATH did not bind to Sepharose-heparin, and the intrinsic fluorescence due to activation of AT in ATH by its heparin chain was reversed at higher [NaCl] than that required to dissociate non-covalent AT.H complexes. Thus, exogenous AT can compete with the AT moiety of ATH for binding to the covalently linked heparin chain, leading to catalytic inhibition of factor Xa or thrombin. These data may suggest that access to pentasaccharide units in non-covalent AT.H complexes by free AT may be facile.

Overexpression of the 78-kDa glucose-regulated protein/immunoglobulin-binding protein (GRP78/BiP) inhibits tissue factor procoagulant activity

Previous studies have demonstrated that overexpression of GRP78/BiP, an endoplasmic reticulum (ER)-resident molecular chaperone, in mammalian cells inhibits the secretion of specific coagulation factors. However, the effects of GRP78/BiP on activation of the coagulation cascade leading to thrombin generation are not known. In this study, we examined whether GRP78/BiP overexpression mediates cell surface thrombin generation in a human bladder cancer cell line T24/83 having prothrombotic characteristics. We report here that cells overexpressing GRP78/BiP exhibited significant decreases in cell surface-mediated thrombin generation, prothrombin consumption and the formation of thrombin-inhibitor complexes, compared with wild-type or vector-transfected cells. This effect was attributed to the ability of GRP78/BiP to inhibit cell surface tissue factor (TF) procoagulant activity (PCA) because conversion of factor X to Xa and factor VII to VIIa were significantly lower on the surface of GRP78/BiP-overexpressing cells. The additional findings that (i) cell surface factor Xa generation was inhibited in the absence of factor VIIa and (ii) TF PCA was inhibited by a neutralizing antibody to human TF suggests that thrombin generation is mediated exclusively by TF. GRP78/BiP overexpression did not decrease cell surface levels of TF, suggesting that the inhibition in TF PCA does not result from retention of TF in the ER by GRP78/BiP. The additional observations that both adenovirus-mediated and stable GRP78/BiP overexpression attenuated TF PCA stimulated by ionomycin or hydrogen peroxide suggest that GRP78/BiP indirectly alters TF PCA through a mechanism involving cellular Ca(2+) and/or oxidative stress. Similar results were also observed in human aortic smooth muscle cells transfected with the GRP78/BiP adenovirus. Taken together, these findings demonstrate that overexpression of GRP78/BiP decreases thrombin generation by inhibiting cell surface TF PCA, thereby suppressing the prothrombotic potential of cells.

Effect of extracellular volume expansion and surgical stress on splanchnic blood flow and cardiac output in anesthetized rats: role of nitric oxide

In a normal volume state, surgical stress decreases rather than increases nitric oxide (NO) production in the vascular system. In our studies, the effect of minor and major surgical stress and three different degrees of volume expansion on systemic and splanchnic circulatory parameters and on the NO dependence of the circulation have been investigated. When the degree of volume expansion was increased, cardiac output and organ blood flow increased without significant change in vascular resistances. Major surgical stress reduced the increase in cardiac output and organ blood flow elicited by the volume expansion. NO synthase (NOS) inhibition significantly increased blood pressure and total peripheral resistance (TPR) and decreased cardiac output in all groups of animals. As the degree of volume expansion was increased, the NO dependence of the circulation in the surgically less- and more-stressed animals was inversely influenced in some cases. With the three degrees of volume expansion (20, 40, and 60 ml/kg), the NOS inhibition increased the TPR from 30.7 R/kg +/- 1.90 to 73.6 R/kg +/- 5.00, from 20.7 R/kg +/- 1.43 to 66.7 R/kg +/- 3.88, and from 19.9 R/kg +/- 1.25 to 49.1 R/kg +/- 3.84 in the surgically less-stressed animals and from 38.6 R/kg +/- 2.14 to 59.8 R/kg +/- 5.62, from 31.9 R/kg +/- 2.70 to 81.7 R/kg +/- 9.89, and from 29.1 R/kg +/- 2.49 to 91.1 R/kg +/- 6.36 in the surgically more-stressed animals. Volume expansion increases the NO dependence of the vascular resistance in the surgically more-stressed animals but decreases it in the surgically less-stressed animals.

Role of angiotensin II in L-NAME-induced systemic and renal hemodynamic effects in hydrochlorothiazide-pretreated hypertensive subjects

BACKGROUND

Experimental evidence suggests that in conditions associated with an activated renin-angiotensin system, unopposed activity of angiotensin II underlies the marked renal vasoconstrictor response to nitric oxide synthase inhibition. In the present study, we investigated whether this holds true in hypertensive subjects pretreated with hydrochlorothiazide (HCT).

METHODS

Systemic N(G)-nitro-L-arginine methyl ester (L-NAME) infusions (12.5 microg/kg per min for 40 min) were given to eight hypertensive subjects (age 53 +/- 6 years) during placebo, and during pretreatment with HCT (25 mg once daily) or HCT and losartan (LOS) (50 mg twice daily), both for 9 days. The glomerular filtration rate (GFR) and renal plasma flow were estimated from the clearances of radiolabeled thalamate and hippuran. Renal blood flow (RBF) was calculated as renal plasma flow/1 - hematocrit and the renal vascular resistance (RVR) as mean arterial pressure (MAP) divided by RBF.

RESULTS

Compared with placebo, plasma renin increased (P < 0.001) from 15 +/- 4 mU/l during placebo to 26 +/- 7 mU/l during HCT and to 133 +/- 51 mU/l during HCT + LOS. MAP (110 +/- 3 mmHg) decreased to 102 +/- 4 mmHg during HCT and to 98 +/- 5 mmHg during HCT + LOS. RBF (579 +/- 36 ml/min), GFR (97 +/- 6 ml/min) and filtration fraction (29 +/- 2%) did not change, whereas RVR (200 +/- 15 RU) decreased to 183 +/- 13 RU during HCT and to 165 +/- 14 RU during HCT + LOS (P < 0.05). In response to L-NAME, MAP and RVR increased maximally by 10 +/- 3 and 67 +/- 9%, whereas RBF and GFR decreased maximally by 42 +/- 6 and 18 +/- 4%. Compared with these responses, the responses of MAP, RBF and RVR were not affected by pretreatment of HCT or HCT + LOS, but the L-NAME-induced decrease in GFR (26 +/- 5% during HCT and 29 +/- 5% during HCT and LOS) was enhanced (P < 0.01).

CONCLUSIONS

In hypertensive subjects with an activated renin-angiotensin system, unopposed activity of angiotensin II is not involved in L-NAME-induced pressor and renal vasoconstrictor response, whereas the L-NAME-induced decrease in GFR is enhanced, indicating greater dependency of GFR on nitric oxide-mediated vasodilator tone during sodium depletion.

Effect of covalent serpin-heparinoid complexes on plasma thrombin generation on fetal distal lung epithelium

Extravascular coagulation within the lung airspace is a hallmark of respiratory distress syndrome (RDS) in premature infants. We previously showed that covalent antithrombin-heparin complex (ATH) is superior to noncovalent antithrombin (AT) + heparin (H) mixtures at inhibiting plasma thrombin generation on rat fetal distal lung epithelium (FDLE) in vitro. However, heparin cofactor II (HC) has been shown to selectively inhibit thrombin, which may be advantageous if other enzyme activities are present in the airspace. We compared the abilities of ATH, covalent HC-heparin complex (HCH), and covalent HC-dermatan sulfate (HCD) to inhibit thrombin generation on FDLE in plasmas from either adults or newborns. In the presence of ATH, peak free thrombin generation in adult plasma on the cell surface was reduced by 92% compared with controls (no anticoagulant). However, whereas HCH reduced peak free thrombin generation in adult plasma by 81%, HCD was only able to reduce activity by 33%. All covalent complexes caused a greater decrease in thrombin activity compared with that with the corresponding noncovalent serpin + heparinoid mixtures. Experiments in plasma from newborns resulted in peak free thrombin that was less than or equal to that in adult plasma when covalent conjugates were added. Relative peak free thrombin was proportional to rate of prothrombin consumption and amount of thrombin-inhibitor complexes formed. In vivo, experiments in newborn rats showed that a greater percentage of intratracheally instilled ATH and HCH could be recovered in lung lavage fluid compared withwith that for HCD. In summary, ATH, HCH, and HCD are inhibitors of thrombin generation on FDLE superior to the corresponding noncovalent mixtures, with ATH and HCH being more potent than HCD. Covalent conjugates of AT or HC with H may be preferred in treatment of extravascular coagulation.

Current Paradigms in Cellular Oxygen Sensing

Organisms, tissues and cells react to hypoxia by activating adaptive responses that tend to preserve systemic oxygen transport, cellular oxygen delivery, and the resistance of cells against the consequences of severe hypoxia. These responses are required for embryonic development and for survival through adulthood. Although much has been learned about the signaling pathways that are activated in hypoxic cells, the underlying mechanism of O2 sensing is not established. Most of the putative models of O2 sensing include the involvement of redox-dependent reactions and many implicate reactive oxygen species in the signaling process. The sources of these oxidant signals are thought to include members of the NAD(P)H oxidase system and/or mitochondria. This article reviews evidence for and against the involvement of these systems in the O2 sensing pathway.

H2O2 activates ryanodine receptor but has little effect on recovery of releasable Ca2+ content after fatigue

We studied whether hydrogen peroxide (H(2)O(2)) at </=10 microM activates the ryanodine receptor and decreases releasable Ca(2+) content in the sarcoplasmic reticulum after fatigue. Exposure of rabbit or frog skeletal muscle ryanodine receptors to 10 microM H(2)O(2) enhanced channel activity in lipid bilayers when the redox potential was defined at cis = -220 mV and trans = -180 mV. Channel activation by 10 microM H(2)O(2) was also observed when cis potential was set at -220 mV without defining trans potential, but the effect was less. Reduction of trans redox potential from -180 to -220 mV did not alter channel activity. H(2)O(2) at 500 microM failed to activate the channel when the redox potential was not controlled. Stimulation of the frog muscle fiber for 2 min (50 Hz, a duty cycle of 200 ms/s) decreased tetanus tension by approximately 50%. After 1 min, tetanus recovered rapidly to approximately 70% of control and thereafter slowly approached the control level. Amplitudes of caffeine- and 4-chloro-m-cresol-induced contractures were decreased after a 60-min rest. The decrease is not enhanced by exposure to 10 microM H(2)O(2). These results suggest that H(2)O(2) markedly activates the ryanodine receptor under the redox control in vitro, but externally applied H(2)O(2) may not play an important role in the postfatigue recovery process.

Age-related increase of pulse pressure and gene polymorphisms in essential hypertension: a preliminary study

Genes may modulate the changes of blood pressure (BP) with age; this possibility has never been studied for the age-related increase of pulse pressure (PP), although in older populations, PP is considered the stronger mechanical factor predicting cardiovascular mortality. In humans, the presence of the mutant allele C of the angiotensin II (Ang II) AT(1)-receptor or of the mutant allele T of the eNOS G(298) T gene polymorphisms is associated with enhanced contractile properties of conduit arteries in response to vasoconstrictive agents. In this study, we evaluated, in subjects with untreated essential hypertension, whether the presence of these mutant alleles or their combination might influence the age-related increase of PP. Three main findings emerged from the study and were particularly observed in women: 1) the presence of the C and/or of the T mutant alleles or their combination were associated with a steeper slope of the age versus PP curve, compared with subjects without the mutant allele; 2) the slope was more significantly enhanced when the two mutant alleles were associated in the same genotype; and 3) no comparable age- and gender-related changes in systolic, diastolic or mean BP were found according to this genetic classification. In subjects with essential hypertension, genes may modulate the age-mediated increase of PP. This finding gives new insights in the interactions between genes, mechanical factors and cardiovascular risk.

Redox states of type 1 ryanodine receptor alter Ca(2+) release channel response to modulators

The type 1 ryanodine receptor (RyR1) from rabbit skeletal muscle displayed two distinct degrees of response to cytoplasmic Ca(2+) [high- and low-open probability (P(o)) channels]. Here, we examined the effects of adenine nucleotides and caffeine on these channels and their modulations by sulfhydryl reagents. High-P(o) channels showed biphasic Ca(2+) dependence and were activated by adenine nucleotides and caffeine. Unexpectedly, low-P(o) channels did not respond to either modulator. The addition of a reducing reagent, dithiothreitol, to the cis side converted the high-P(o) channel to a state similar to that of the low-P(o) channel. Treatment with p-chloromercuriphenylsulfonic acid (pCMPS) transformed low-P(o) channels to a high-P(o) channel-like state with stimulation by beta,gamma-methylene-ATP and caffeine. In experiments under redox control using glutathione buffers, shift of the cis potential toward the oxidative state activated the low-P(o) channel, similar to that of the high-P(o) or the pCMPS-treated channel, whereas reductive changes inactivated the high-P(o) channel. Changes in trans redox potential, in contrast, did not affect channel activity of either channel. In all experiments, channels with higher P(o) were stimulated to a great extent by modulators, but ones with lower P(o) were unresponsive. These results suggest that redox states of critical sulfhydryls located on the cytoplasmic side of the RyR1 may alter both gating properties of the channel and responsiveness to channel modulators.

Hydrogen peroxide increases depolarization-induced contraction of mechanically skinned slow twitch fibres from rat skeletal muscles

The effect of exogenous hydrogen peroxide (H(2)O(2)) on excitation-contraction (E-C) coupling and sarcoplasmic reticulum (SR) function was compared in mechanically skinned slow twitch fibres (prepared from the soleus muscles) and fast twitch fibres (prepared from the extensor digitorum longus; EDL muscles) of adult rats. Equilibration (5 min) with 1 mM H(2)O(2) diminished the ability of the Ca(2+)-depleted SR to reload Ca(2+) in both slow (P < 0.01) and fast twitch fibres (P < 0.05) compared to control. Under conditions when all Ca(2+) uptake was prevented, 1 mM H(2)O(2) increased SR Ca(2+) "leak" in fast twitch fibres by 24 +/- 5 % (P < 0.05), but leak was not altered in slow twitch fibres. Treatment with 1 mM H(2)O(2) also increased the peak force of low [caffeine] contracture by approximately 45% in both fibre types compared to control (P < 0.01), which could be partly reversed following treatment with 10 mM dithiothreitol (DTT). The changes in SR function caused by 1 mM H(2)O(2) were associated with an approximately 65% increase in the peak height of depolarization-induced contractile response (DICR) in slow twitch fibres, compared to control (no H(2)O(2); P < 0.05). In contrast, peak contractile force of fast twitch fibres was not altered by 1 mM H(2)O(2) treatment. Equilibration with 5 mM H(2)O(2) induced a spontaneous force response in both slow and fast twitch fibres, which could be partly reversed by 2 min treatment with 10 mM DTT. Peak DICR was also increased approximately 40% by 5 mM H(2)O(2) in slow twitch fibres compared to control (no H(2)O(2); P < 0.05). Our results indicate that exogenous H(2)O(2) increases depolarization-induced contraction of mechanically skinned slow but not fast twitch fibres. The increase in depolarization-induced contraction in slow twitch fibres might be mediated by an increased SR Ca(2+) release during contraction and/or an increase in Ca(2+) sensitivity.

Impact of NO-synthase inhibition on renal hemodynamics in normotensive and hypertensive subjects

OBJECTIVE

To examine the acute effects of NO-synthase inhibition on renal hemodynamics in normotensive and hypertensive subjects.

METHODS

Changes of renal plasma flow (RPF) and glomerular filtration rate (GFR) in response to intravenous infusions of NG-monomethyl-l-arginine (l-NMMA) (3 mg/kg per 30 min) were measured in 32 normotensive and in 39 essential hypertensive patients by use of clearance technique.

RESULTS

l-NMMA significantly decreased RPF in normotensive and hypertensive individuals (P < 0.001), while GFR was preserved. Changes of renal hemodynamic parameters were similar in hypertensive and normotensive subjects (deltaRPF: -88 +/- 89 versus -81 +/- 105 ml/min, P = NS; deltaGFR 1.6 +/- 8.2 versus 4.3 +/- 8.9 ml/min, P = NS) Furthermore, l-NMMA increased mean arterial pressure (deltaMAP 5.3 +/- 6.3 versus 6.0 +/- 6.1 mmHg, P = NS) and decreased heart rate (deltaHR -5.8 +/- 3.9 versus -4.1 +/- 3.8 beats/min, P = NS) to a similar extent in both groups.

CONCLUSION

Basal NO synthesis of the renal vasculature is not impaired in patients with established essential hypertension.

XOD-catalyzed ROS generation mobilizes calcium from intracellular stores in mouse pancreatic acinar cells

In fura-2 loaded isolated mouse pancreatic acinar cells, xanthine oxidase (XOD)-catalyzed reactive oxygen species (ROS) generation caused an increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)) by release of Ca(2+) from intracellular stores. The ROS-induced Ca(2+) signals showed large variability in shape and time-course and resembled in part Ca(2+) signals in response to physiological secretagogues. ROS-induced Ca(2+) mobilization started at the luminal cell pole and spread towards the basolateral side in a wave manner. ROS-evoked Ca(2+) responses were not inhibited by the phospholipase C (PLC) inhibitor U73122 (10 microM). Neither 2-aminoethoxy-diphenylborate (2-APB) (70 microM) nor ryanodine (50 microM) suppressed ROS-evoked Ca(2+) release. ROS still released Ca(2+) when the endoplasmic reticulum Ca(2+)-ATPase was blocked with thapsigargin (1 microM), or when rotenone (10 microM) was added to release Ca(2+) from mitochondria. Our results suggest that pancreatic acinar cells ROS do not unspecifically affect Ca(2+) homeostasis. ROS primarily affect Ca(2+) stores located in the luminal cell pole, which is also the trigger zone for agonist-induced Ca(2+) signals. Release of Ca(2+) induces Ca(2+) waves carried by Ca(2+)-induced Ca(2+) release and produces thereby global Ca(2+) signals. Under oxidative stress conditions, the increase in [Ca(2+)](i) could be one mechanism contributing to an overstimulation of the cell which could result in cell dysfunction and cell damage.

Increased dietary salt activates rat aortic endothelium

The function of vascular endothelium as a biomechanical sensor permits alterations in gene expression in the vascular tree in response to wall stress. The present study explored the mechanism by which the arterial endothelium responds to changes in dietary salt. Normotensive rats were fed diets containing varying amounts of NaCl for 4 days. At that time, levels of phosphorylated p38 MAP kinase, p42/44 MAP kinase, and p46/54 JNK/SAP kinase increased when the diet contained > or = 3.0% NaCl. Kinase assays demonstrated dose-response relationships between dietary salt intake and the activities of p38 MAP kinase and p42/44 MAP kinase. Aortic segments from animals on the 8.0% NaCl diet produced greater amounts of total and active transforming growth factor-beta 1 (TGF-beta1) and nitric oxide. The MEK1 inhibitor, PD-098059, and the p38 MAP kinase inhibitor, SB-203580, decreased production of these bioactive compounds to background levels. Intravenous injection of tetraethylammonium chloride (TEA) into rats on the 8.0% NaCl diet decreased the activities of p38 MAP kinase and p42/44 MAP kinase, compared with rats on the same diet and given vehicle intravenously. These findings provided direct evidence that dietary salt modulated gene expression in the arterial wall through a tetraethylammonium-sensitive mechanism and activation of the p38 and p42/44 MAP kinase pathways.

Diet-induced mild hyperhomocysteinemia and increased salt intake diminish vascular endothelial function in a synergistic manner

OBJECTIVES

We investigated the influence of hyperhomocysteinemia and high salt intake on sodium handling, oxidative state, vascular endothelial function and blood pressure in a rat model.

METHODS

Eight-week-old male Sprague-Dawley rats were divided into subgroups and maintained for 4 weeks prior to experimentation on either control chow containing 0.36% methionine and 0.5% NaCl; or one of the following modified diets containing either 0.7% methionine, 8% NaCl or 0.7% methionine + 8% NaCl. Sodium handling, homocysteine metabolism, lipid profile, NO synthesis, oxidative state, blood pressure and relaxation to acetylcholine of carotid rings were evaluated and compared.

RESULTS

Diet-induced mild hyperhomocysteinemia (plasma homocysteine levels 1.4-fold higher than control), by itself, had no significant influence on sodium excretion, vascular endothelial function and blood pressure. Increased salt intake had no influence on homocysteine metabolism, vascular endothelial function and blood pressure. The coexistence of mild hyperhomocysteinemia and high salt intake significantly diminished vascular endothelial function (rmax to acetylcholine; control chow 83.2 +/- 6.2%, 0.7% methionine diet 74.7 +/- 3.9%, 8% NaCl diet 85.1 +/- 4.6%, 0.7% methionine + 8% NaCl diet 57.9 +/- 6.6%) but manifested no rise in blood pressure. No significant difference in oxidative state was observed in this analysis.

CONCLUSIONS

Diet-induced mild hyperhomocysteinemia, the extent of which is comparable with the levels that are associated with a predisposition to common atherosclerotic diseases, was found to induce vascular endothelial dysfunction only when accompanied by high salt intake.

Early activation of inflammation and clotting in the preterm lamb with neonatal RDS: comparison of conventional ventilation and high frequency oscillatory ventilation

In neonatal respiratory distress syndrome activation of inflammation and clotting is demonstrated. High frequency oscillatory ventilation (HFOV) is considered to be less damaging to the human preterm lung, resulting in less activation of inflammation and clotting compared with conventional ventilation (CV). To assess the sequence of events of activation of inflammation and clotting and to compare the impact of HFOV to CV, we ventilated preterm lambs delivered by cesarean section at 132 d gestational age (term 145 d) for 8 h by CV (n = 10) or HFOV (n = 11). Fifteen minutes after birth and at 2-h intervals thereafter blood samples, from umbilical catheters, were analyzed for AP50 (complement activation), number of polymorphonuclear leukocytes, beta-glucuronidase, platelet function, activated partial thromboplastin time, thrombin time and thrombin inhibition, and bronchoalveolar lavage fluid was analyzed for elastase, thrombin and protein. We found complement activation, low number of polymorphonuclear leukocytes and high levels of beta-glucuronidase already at 15 min after birth. Within 2 to 4 h after birth platelet function deteriorated, activated partial thromboplastin time prolonged, and thrombin inhibition decreased. Activation of inflammation and clotting in the lungs was demonstrated by increased levels of elastase and thrombin in bronchoalveolar lavage fluid. In the HFOV group, AP50 remained significantly higher than in the CV group, reflecting less complement activation, and platelet function analysis remained significantly lower, reflecting better platelet function. We conclude that systemic activation of inflammation can be found in the ventilated preterm lamb with respiratory distress syndrome within 15 min after birth. Afterward, or due to activation of inflammation, clotting is activated. HFOV possibly attenuates activation of inflammation.

Hydrogen peroxide modulates Ca2+-activation of single permeabilized fibres from fast- and slow-twitch skeletal muscles of rats

We examined the effects of redox modulation on single membrane-permeabilized fibre segments from the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles of adult rats to determine whether the contractile apparatus was the redox target responsible for the increased contractility of muscles exposed to low concentrations of H2O2. The effects of H2O2 on maximum Ca2+-activated force were dose-dependent with 30 min exposure to 5 mM H2O2 causing a progressive decrease by 22+/-3 and 13+/-2% in soleus and EDL permeabilized muscle fibres, respectively. Lower concentrations of exogenous H2O2 (100 microM and 1 mM) had no effect on maximum Ca2+-activated force. Subsequent exposure to the reductant dithiothreitol (DTT, 10 mM, 10 min) fully reversed the H2O2-induced depression of force in EDL, but not in soleus muscle fibres. Incubation with DTT alone for 10 min did not alter Ca2+-activated force in either soleus or EDL muscle fibres. The sensitivity of the contractile filaments to Ca2+ (pCa50) was not altered by exposure to any concentration of exogenous H2O2. However, all concentrations of H2O2 diminished the Hill coefficient in permeabilized fibres from the EDL muscle, indicating that the cooperativity of Ca2+ binding to troponin is altered. H2O2 (5 mM) did not affect rigor force, which indicates that the number of crossbridges participating in contraction was not reduced. In conclusion, H2O2 may reduce the maximum Ca2+ activated force production in skinned muscle fibres by decreasing the force per crossbridge.

Contribution of nitric oxide to arterial pressure and heart rate variability in rats submitted to high-sodium intake

The aim of this study was to determine the contribution of NO to arterial pressure and heart rate variability in normotensive rats subjected to high sodium intake. Arterial pressure, heart rate, and arterial pressure and heart rate variability, baroreflex sensitivity, and pressure responsiveness were measured in male Wistar rats treated for 6 weeks (control and high sodium [1%] intake groups), before and after acute NO synthesis blockade. After treatment, no changes were observed in arterial pressure or heart rate. Arterial pressure variability was increased after sodium intake; however, heart rate variability and baroreflex sensitivity were not modified in high-sodium rats. NO synthase blockade increased arterial pressure in both groups but was higher in the high-sodium group (from 110+/-5 to 162+/-1.5 mm Hg) compared with the control group (from 109+/-6.7 to 144+/-10 mm Hg). The increase in arterial pressure was accompanied by a decrease in heart rate (from 354+/-28 to 303+/-25 bpm in control rats and from 380+/-34 to 298+/-30 bpm in high-sodium rats). NO synthase blockade increased the tachycardic response to sodium nitroprusside in high-sodium rats. Arterial pressure variability, evaluated by a nonlinear method (3D return maps), showed a larger reduction in response to NO synthase inhibition in the high-sodium group (from 162+/-26 to 34.8+/-8.6 for general index of beat-to-beat blood pressure variability) than in the control group (from 58+/-9.6 to 36+/-4.7 for general index of beat-to-beat blood pressure variability). Heart rate variability, evaluated by the SD of the R-R intervals, was not changed in control rats but was increased by NO synthase inhibition in the high-sodium rats (from 9.5+/-0.2 to 21.9+/-1.7 milliseconds). These findings suggest an important role for increased NO production in adaptation to high-sodium intake. The increase in NO system sensitivity in high-sodium intake may contribute to changes in the autonomic nervous system regulating heart rate and, especially, arterial pressure variability.

Nitric oxide synthase (NOS2) mutation in Dahl/Rapp rats decreases enzyme stability

The pathogenesis of salt-sensitive hypertension remains poorly defined, but a role for nitric oxide (NO) has been suggested. The Dahl/Rapp salt-sensitive rat possesses a defect in NO synthesis that is overcome by supplementation with L-arginine, which increases NO and cGMP production and prevents salt-sensitive hypertension. An S714P mutation of inducible NO synthase (NOS2) was subsequently identified. The current report examined the functional significance of an S714P mutation in NOS2. COS-7 cells were transiently transfected with cDNA of wild-type NOS2 and S714P and S714A mutants of NOS2, and enzyme function was determined. Whereas steady-state mRNA levels did not differ, immunoblot analysis demonstrated decreased levels of NOS2 protein. Metabolic labeling experiments confirmed a reduced half-life of the S714P mutation. Nitrite production, which was dependent on the concentration of L-arginine in the medium, was diminished in cells transfected with the S714P mutant, compared with the wild type and the S714A mutant. These data provide a biochemical explanation of the physiological abnormalities of NOS2 in the Dahl/Rapp salt-sensitive rat and suggest that a posttranslational mechanism involving the proteasome may be responsible for the diminished NO production observed in response to increased dietary salt intake in these animals.

Angiotensin II and prostaglandin interactions on systemic and renal effects of L-NAME in humans

For investigation of whether interactions between prostaglandins and angiotensin II modulate renal response to acute nitric oxide synthesis inhibition in humans, seven young volunteers who were kept on a 240-mM Na diet underwent four experiments with 90 min of infusion of 3.0 microg/kg.min(-1) NG-nitro-L-arginine methyl ester (L-NAME), each preceded by a 3-d treatment with placebo (PL), 50 mg of losartan (LOS), 75 to 125 mg of indomethacin (IND), or both drugs. Mean arterial pressure (MAP), GFR, effective renal plasma flow (ERPF), and Na excretion rate (UNaV) were measured at baseline and from 0 to 45 min and 45 to 90 min of L-NAME infusion. After PL, L-NAME reduced GFR by 5% at 45 min (P < 0.05) and by 9% at 90 min (P < 0.001), ERPF by 11 to 17% (P < 0.001), and UNaV by 28 to 45% (P < 0.001). MAP, unchanged at 45 min, rose by 5% (P < 0.001) at 90 min. LOS prevented pressor but not renal effects of L-NAME. With L-NAME+IND, MAP rose even at 45 min (+5%; P < 0.001 versus baseline) with a 10% rise at 90 min (P < 0.001). Changes in GFR (-13 to -20%), ERPF (-19 to -26%), and UNaV (-51 to -70%) were greater than those with L-NAME+PL or L-NAME+LOS (P < 0.05 to 0.001). With L-NAME+IND+LOS, MAP did not increase, and GFR, ERPF, and UNaV fell much less than with L-NAME+IND alone (P < 0.02 to 0.001) with no differences versus PL or LOS alone. Angiotensin II blockade does not affect renal changes caused by L-NAME but prevents their potentiation by prostaglandin inhibition. Thus, endogenous prostaglandins counteract renal actions of endogenous angiotensin II in Na-repleted humans even when nitric oxide synthesis is inhibited.

Classes of thiols that influence the activity of the skeletal muscle calcium release channel

The skeletal muscle Ca(2+) release channel/ryanodine receptor (RyR1) is a prototypic redox-responsive ion channel. Nearly half of the 101 cysteines per RyR1 subunit are kept in a reduced (free thiol) state under conditions comparable with resting muscle. Here we assessed the effects of physiological determinants of cellular redox state (oxygen tension, reduced (GSH) or oxidized (GSSG) glutathione, and NO/O(2) (released by 3-morpholinosydnonimine)) on RyR1 redox state and activity. Oxidation of approximately 10 RyR1 thiols (from approximately 48 to approximately 38 thiols/RyR1 subunit) had little effect on channel activity. Channel activity increased reversibly as the number of thiols was further reduced to approximately 23/subunit, whereas more extensive oxidation (to approximately 13 thiols/subunit) inactivated the channel irreversibly. Neither S-nitrosylation nor tyrosine nitration contributed to these effects. The results identify at least three functional classes of RyR1 thiols and suggest that 1) the channel may be protected from oxidation by a large reservoir of functionally inert thiols, 2) the channel may be designed to respond to moderate oxidative stress by a change in activation setpoint, and 3) the channel is susceptible to oxidative injury under more extensive conditions.

H(2)O(2) and ethanol act synergistically to gate ryanodine receptor/calcium-release channel

We examined the effect of low concentrations of H(2)O(2) on the Ca(2+)-release channel/ryanodine receptor (RyR) to determine if H(2)O(2) plays a physiological role in skeletal muscle function. Sarcoplasmic reticulum vesicles from frog skeletal muscle and type 1 RyRs (RyR1) purified from rabbit skeletal muscle were incorporated into lipid bilayers. Channel activity of the frog RyR was not affected by application of 4.4 mM (0.02%) ethanol. Open probability (P(o)) of such ethanol-treated RyR channels was markedly increased on subsequent addition of 10 microM H(2)O(2). Increase of H(2)O(2) to 100 microM caused a further increase in channel activity. Application of 4.4 mM ethanol to 10 microM H(2)O(2)-treated RyRs activated channel activity. Exposure to 10 or 100 microM H(2)O(2) alone, however, failed to increase P(o). Synergistic action of ethanol and H(2)O(2) was also observed on the purified RyR1 channel, which was free from FK506 binding protein (FKBP12). H(2)O(2) at 100-500 microM had no effect on purified channel activity. Application of FKBP12 to the purified RyR1 drastically decreased channel activity but did not alter the effects of ethanol and H(2)O(2). These results suggest that H(2)O(2) may play a pathophysiological, but probably not a physiological, role by directly acting on skeletal muscle RyRs in the presence of ethanol.

Hydrogen peroxide decelerates recovery of action potential after high-frequency fatigue in skeletal muscle

Effects of reactive oxygen species (ROS), especially hydrogen peroxide (H(2)O(2)), on recovery of action potential by resting for 30 min after high-frequency fatigue were studied using frog skeletal muscle fibers. After stimulation at a frequency of 50 HZ for 2 min, the action potential amplitude was decreased by 14.5 mV from controls, and resting membrane was depolarized by 15.4 mV. Action potential duration was also prolonged by high-frequency stimulation (1.5 ms in controls to 2.6 ms). The high-frequency stimulation used here caused no muscle damage. The action potential was partially improved after a 30-min rest. Addition of catalase at 500 units/ml or H(2)O(2) at 0.5 mM to sartorius muscle did not alter any of the parameters of the action potential after high-frequency stimulation. Treatment with catalase accelerated post-fatigue recovery of the action potential. Application of H(2)O(2) delayed post-fatigue recovery of resting and action potentials. When added to detubulated toe muscle fibers, catalase no longer improved the attenuation of action potential induced by high-frequency stimulation, even after a 30-min rest. These findings suggest that removal of H(2)O(2) from transverse tubules is effective for post-fatigue recovery of action potential in skeletal muscle.

Effects of antioxidants on calcium signal induced by cholecystokinin in mouse pancreatic acinar cells

Digital imaging fluorescence microscopy was used to study the effect of two antioxidants, N-acetyl-cysteine (NAC) and glutathione, on the cytosolic free calcium concentration ([Ca2+]i) induced by cholecystokinin-octapeptide (CCK-8) of mouse pancreatic acinar cells. When acinar cells were preincubated with either NAC or glutathione, subsequent stimulation with CCK-8 in the presence of each antioxidant had no significant effect on the typical pattern of [Ca2+]i transient evoked by the gastrointestinal hormone. However, application of NAC to acinar cells pretreated for 60 min with the same antioxidant, strongly blocked the oscillatory pattern initiated by CCK-8, inhibiting both amplitude and frequency of calcium oscillations. By contrast, glutathione had no effect on the oscillatory pattern evoked by CCK-8. The present results allow us to speculate that during [Ca2+]i oscillation there is a production of oxidants that facilitate oscillations by enhancing release of calcium from internal stores.

Effects of sodium intake on the pressor and renal responses to nitric oxide synthesis inhibition in normotensive individuals with different sodium sensitivity

OBJECTIVE

The present study evaluated the role of nitric oxide (NO) in the systemic vascular and renal adaptation to changes in dietary sodium intake.

DESIGN AND METHODS

Seven healthy normotensive male subjects were randomized to high or low sodium diets in a double blind crossover design (7 days on each diet). The NO synthesis inhibitor, NGmonomethyl-L-arginine (L-NMMA) was infused systemically (1.8 mg/kg over 30 min) at the end of each dietary period and its effects on blood pressure, renal plasma flow, glomerular filtration rate, urinary flow rate and sodium excretion were measured.

RESULTS

Blood pressure increased in response to L-NMMA on a high sodium diet only (area under time curve percentage change in mean blood pressure, low sodium = -94.5 +/- 164.3; high sodium = 391.1 +/- 228.6; P < 0.05 low versus high). The increase in blood pressure was directly and significantly associated with the individual salt sensitivity, defined by the difference in systemic mean blood pressure between high and low sodium diets (r = 0.756; P < 0.05). L-NMMA also reduced renal plasma flow and urinary flow rate in subjects on high sodium diet.

CONCLUSIONS

The data support a significant influence of endogenous NO in the systemic and renal vascular adaptation to a high sodium diet in normotensive men. In addition, the direct association between the individual sodium-sensitivity and the pressor response to L-NMMA suggests that there is increased dependence of vascular tone on NO in normotensive subjects whose blood pressure is more sodium sensitive.

Oxidative modification of ion channel activity of ryanodine receptor

The ryanodine receptor (RyR) is involved in the physiological Ca2+ release from the sarcoplasmic reticulum in both skeletal and cardiac muscles. The redox regulation is a plausible endogenous regulatory mechanism of the RyR. Sulfhydryl oxidation or S-nitrosylation of the cardiac RyR has been reported to activate the channel. Our laboratory demonstrated that hydroxyl radicals also activate the cardiac Ca2+-release channel activity, likely through the modification of sulfhydryl groups of the RyR.