scholarly journals Non-Central Influences of α2-Adrenergic and Imidazoline Agonist Interactions in Isolated ardiomyocytes Cardiac Cells

Kardiologiia ◽  
2019 ◽  
Vol 59 (4) ◽  
pp. 52-63 ◽  
Author(s):  
A. V. Maltsev ◽  
Y. M. Kokoz
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Adrenergic Receptors ◽  
Left Ventricular ◽  
Cardiac Cells ◽  
Imidazoline Receptors ◽  
Signal Molecule ◽  
Significant Stimulation ◽  
Patch Configuration

Aim: to investigate the functional interaction of α2-adrenergic and imidazoline receptors recently identified on the sarcolemma of isolated cardiomyocytes for regulation of the intracellular calcium and the production of the signal molecule of nitric oxide (NO).Materials and methods:experiments were performed on isolated left ventricular cardiomyocytes of Wistar rats. Potential-dependent Ca2+-currents were measured from the whole-cell by the patch-clamp method in “perforated-patch” configuration. The intracellular calcium and the production of nitric oxide were estimated from the changes in fluorescence intensity of the Ca2+-specific and NO-sensitive dyes at fluorescent or confocal microscope.Results:It has been shown that α2‑adrenergic and imidazoline receptor agonists inhibit L-type Ca2+-currents by themselves, but their effects do not develop against each other’s background. The blockade of key effector molecules: protein kinase B (Akt kinase) for α2‑adrenergic receptors, and protein kinase C for imidazoline receptors causes the action of agonists to become additive. Both the selective α2‑agonist, guanabenz, and the specific agonist of the first type imidazoline receptors, rilmenidine, show an additional inhibition of Ca2+-currents against the basal background already reduced by the activation of one of the two receptor systems. Wherein rilmenidine increases the level of free  Ca2+in the cytosol, and guanabenz, on the contrary, decreases it. The action of guanabenz does not develop against the background of rilmenidine, although it, in turn, effectively increases the intracellular level of calcium in guanabenz-pretreated cardiac cells. Activation of α2‑adrenergic receptors leads to significant stimulation of the endothelial isoform of NO-synthase, and as a result to an increase in the NO level. Activation of imidazoline receptors itself does not affect NO synthesis but it prevents the production of NO induced by α2‑agonists.Conclusion:obtained data make it possible to formulate a number of useful recommendations for clinical practice, and also to clarify the non-central peripheral effects arising from the activation of α2‑adrenergic or imidazoline systems under conditions of endogenous hyperactivation on of the two systems.

Abstract 15295: Molecular Mechanism of Chronic Sildenafil-Caused Regression of Heart Failure: Effects on the Express of Cardiac SR Ca2+-ATPase, Subtype of β-Adrenergic Receptors and Nitric Oxide Synthase Isoforms

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Heng-Jie Cheng ◽  
Tiankai Li ◽  
Che Ping Cheng
Keyword(s):  
Nitric Oxide ◽  
Heart Failure ◽  
Nitric Oxide Synthase ◽  
Adrenergic Receptors ◽  
Left Ventricular ◽  
Male Rats ◽  
Protein Levels ◽  
Myocyte Function ◽  
Oxide Synthase ◽  
Β Adrenergic Receptors

Background: Sildenafil (SIL), a selective inhibitor of PDE5 has been shown to exert profound beneficial effects in heart failure (HF). Recently we further found that SIL caused regression of cardiac dysfunction in a rat model with isoproterenol (ISO)-induced progressive HF. However, the molecular basis is unclear. We hypothesized that reversal of HF-induced detrimental alterations on the expressions of cardiac SR Ca 2+ -ATPase (SERCA2a), β-adrenergic receptors (AR) and nitric oxide synthase (NOS) isoforms by SIL may play a key role for its salutary role in HF. Methods: Left ventricular (LV) and myocyte function and the protein levels of myocyte β 1 - and β 3 - AR, SERCA2a, phospholamban (PLB) and three NOS were simultaneously evaluated in 3 groups of male rats (6/group): HF , 3 months (M) after receiving ISO (170 mg/kg sq for 2 days); HF/SIL , 2 M after receiving ISO, SIL (70 μg/kg/day sq via mini pump) was initiated and given for 1 M; and Controls (C). Results: Compared with controls, ISO-treated rats progressed to severe HF at 3 M after ISO followed by significantly decreased LV contractility (E ES , HF: 0.7 vs C: 1.2 mmHg/μl) and slowed LV relaxation, reductions in the peak velocity of myocyte shortening (77 vs 136 μm/sec), relengthening (62 vs 104 μm/sec) and [Ca 2+ ] iT (0.15 vs 0.24) accompanied by a diminished myocyte inotropic response to β-AR agonist, ISO (10 -8 M). These abnormalities were associated with concomitant significant decreases in myocyte protein levels of β 1 -AR (0.23 vs 0.64), SERCA2a (0.46 vs 0.80), PLB Ser16 /PLB ratio (0.24 vs 0.40) and eNOS (0.28 vs 0.46), but significantly increases in protein levels of β 3 -AR (0.29 vs 0.10) and iNOS (0.18 vs 0.08) with relatively unchanged nNOS. Chronic SIL prevented the HF-induced decreases in LV and myocyte contraction, relaxation, peak [Ca 2+ ] iT , and restored normal myocyte contractile response to ISO stimulation. With SIL, protein levels of myocyte β 1 - and β 3 -AR, SERCA2a were restored close to control values, but eNOS was significantly elevated than controls (0.77). Conclusions: Chronic SIL prevents HF-caused downregulation of cardiac β 1 -AR and reverse contrast changes between iNOS and β 3 -AR with SERCA 2a and eNOS expression, leading to the preservation of LV and myocyte function, [Ca 2+ ] iT , and β-adrenergic reserve.

Abstract 337: Activation of Myocardial AMP-activated Protein Kinase by Metformin Prevents Progression of Heart Failure in Dogs; Involvement of eNOS Activation

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Hideyuki Sasaki ◽  
Hiroshi Asanuma ◽  
Masashi Fujita ◽  
Hiroyuki Takahama ◽  
Masanori Asakura ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Nitric Oxide ◽  
Heart Failure ◽  
Cell Death ◽  
Protein Kinase ◽  
Left Ventricular ◽  
Vehicle Group ◽  
Mrna Levels ◽  
Compound C ◽  
Amp Activated Protein Kinase

Background; Several studies have shown that metformin activates AMP-activated protein kinase (AMPK), which mediates potent cardioprotection against ischemia-reperfusion injury. AMPK is also activated in experimental failing myocardium, suggesting that activation of AMPK is beneficial for the pathophysiology of heart failure. We investigated whether metformin prevents oxidative stress-induced cell death in rat cardiomyocytes and attenuates the progression of heart failure in dogs. Methods and Results; The treatment with metformin (10 μmol/L) protected the rat cultured cardiomyocytes against cell death due to H 2 O 2 exposure (50 μmol/L) as indicated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), TUNEL staining, and flow cytometry. These effects were blunted by an AMPK inhibitor, compound-C (20 μmol/L), suggesting that the activation of AMPK decreased the extent of apoptosis-induced cell death due to H 2 O 2 exposure. Continuous rapid ventricular pacing (230/min for 4 weeks) in dogs caused heart failure and the treatment with metformin (100 mg/kg/day PO, n=8) decreased left ventricular (LV) end-diastolic dimension (32.8±0.4 vs. 36.5±1.0 mm, p< 0.01) and pressure (11.8±1.1 vs. 22±0.9 mmHg, p< 0.01), and increased LV fractional shortening (18.6±1.8 vs. 9.6±0.7 %, p< 0.01) along with enhanced phosphorylation of AMPK and the decreased the number of TUNEL-positive cells of the LV myocardium compared with the vehicle group (n=8). Interestingly, metformin increased the protein and mRNA levels of endothelial nitric oxide synthase of the LV myocardium and plasma nitric oxide levels. Metformin improved the plasma insulin resistance without increased myocardial GLUT-4 translocation. Furthermore, the subcutaneous administration of AICAR (50 mg/kg/every other day), another AMPK activator mediated the equivalent effects to metformin, strengthening the pivotal role of AMPK in reduction of apoptosis and prevention of heart failure. Conclusions; Activation of myocardial AMPK attenuated the oxidative stress-induced cardiomyocyte apoptosis and prevented the progression of heart failure in dogs, along with eNOS activation. Thus, metformin or AICAR may be applicable as a novel therapy for heart failure.

Human recombinant chromogranin A-derived vasostatin-1 mimics preconditioning via an adenosine/nitric oxide signaling mechanism

2007 ◽  
Vol 293 (1) ◽  
pp. H719-H727 ◽  
Author(s):  
Sandra Cappello ◽  
Tommaso Angelone ◽  
Bruno Tota ◽  
Pasquale Pagliaro ◽  
Claudia Penna ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase ◽  
Rat Heart ◽  
Chromogranin A ◽  
Soluble Guanylate Cyclase ◽  
Left Ventricular ◽  
Inotropic Effect ◽  
Rate Pressure Product ◽  
Protective Effects ◽  
Nitric Oxide Signaling

The acidic protein chromogranin A (CgA) is the precursor of several regulatory peptides generated by specific proteolytic processes. Human recombinant CgA NH2-terminal fragment STA-CgA1-78 (hrSTA-CgA1-78), containing vasostatin-1 (CgA1-76) domain, exerts a negative inotropic effect and counteracts the β-adrenergic positive inotropic effect on the rat heart. We hypothesized an involvement of nitric oxide (NO)-dependent pathway in both cardiodepression and cardioprotection by hrSTA-CgA1-78. We also hypothesized an involvement of adenosine A1 receptor and protein kinase C (PKC) in cardioprotection by hrSTA-CgA1-78. Therefore, we evaluated whether 1) the cardioinhibition mediated by hrSTA-CgA1-78 involves the Gi/o proteins/NO-dependent signal transduction cascade, 2) hrSTA-CgA1-78 induces ischemic preconditioning-like protective effects on the myocardium, and 3) inhibition of NO synthase (NOS), adenosine A1 receptor, or PKC affects hrSTA-CgA1-78 protection. Using the isolated rat heart, we found that the reduction of left ventricular pressure (LVP), rate-pressure product, and maximal values of the first derivative of LVP elicited by hrSTA-CgA1-78 at 33 nM is abolished by blocking Gi/o proteins with pertussis toxin, scavenging NO with hemoglobin, and blocking NOS activity with NG-monomethyl-l-arginine or N5-(iminoethyl)-l-ornithine, soluble guanylate cyclase with 1 H-[1,2,4]oxadiazole-[4,4-a]quinoxalin-1-one, and protein kinase (PKG) with KT5823. Data suggest the involvement of the Gi/o proteins/NO-cGMP-PKG pathway in the hrSTA-CgA1-78-dependent cardioinhibition. When given before 30 min of ischemia, hrSTA-CgA1-78 significantly reduced the size of the infarct from 64 ± 4 to 32 ± 3% of the left ventricular mass. This protective effect was abolished by either NOS inhibition or PKC blockade and was attenuated, but not suppressed, by the blockade of A1 receptors. These results suggest that hrSTA-CgA1-78 activity triggers two different pathways: one of these pathways is mediated by A1 receptors, and the other is mediated by NO release. As with repeated brief preconditioning ischemia, hrSTA-CgA1-78 may be considered a stimulus strong enough to trigger both pathways, which may converge on PKC.

scholarly journals Adrenomedullin Stimulates Nitric Oxide Release from SK-N-SH Human Neuroblastoma Cells by Modulating Intracellular Calcium Mobilization

Endocrinology ◽  
2005 ◽  
Vol 146 (5) ◽  
pp. 2295-2305 ◽  
Author(s):  
Yong Xu ◽  
Teresa L. Krukoff
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Protein Kinase A ◽  
Neuroblastoma Cells ◽  
No Synthase ◽  
Human Neuroblastoma Cells ◽  
Human Neuroblastoma ◽  
No Release ◽  
Kinase A

Abstract We used SK-N-SH human neuroblastoma cells to test the hypothesis that adrenomedullin (ADM), a multifunctional neuropeptide, stimulates nitric oxide (NO) release by modulating intracellular free calcium concentration ([Ca2+]i) in neuron-like cells. We used a nitrite assay to demonstrate that ADM (10 pm to 100 nm) stimulated NO release from the cells, with a maximal response observed with 1 nm at 30 min. This response was blocked by 1 nm ADM22–52, an ADM receptor antagonist or 2 μm vinyl-l-NIO, a neuronal NO synthase inhibitor. In addition, 5 μm 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl ester, an intracellular calcium chelator, eliminated the ADM-induced NO release. Similar results were observed when the cells were incubated in calcium-free medium or when l-type calcium channels were inhibited with 5 μm nifedipine or 10 μm nitrendipine. Depletion of calcium stores in the endoplasmic reticulum (ER) with 1 μm cyclopiazonic acid or 150 nm thapsigargin, or inhibition of ryanodine-sensitive receptors in the ER with 10 μm ryanodine attenuated the ADM-induced NO release. NO responses to ADM were mimicked by 1 mm dibutyryl cAMP, a cAMP analog, and were abrogated by 5 μm H-89, a protein kinase A inhibitor. Furthermore, Fluo-4 fluorescence-activated cell sorter analysis showed that ADM (1 nm) significantly increased [Ca2+]i at 30 min. This response was blocked by nifedipine (5 μm) or H-89 (5 μm) and was reduced by ryanodine (10 μm). These results suggest that ADM stimulates calcium influx through l-type calcium channels and ryanodine-sensitive calcium release from the ER, probably via cAMP-protein kinase A-dependent mechanisms. These elevations in [Ca2+]i cause activation of neuronal NO synthase and NO release.

Caveolin-1 peptide exerts cardioprotective effects in myocardial ischemia-reperfusion via nitric oxide mechanism

2001 ◽  
Vol 280 (6) ◽  
pp. H2489-H2495 ◽  
Author(s):  
Lindon H. Young ◽  
Yasuhiko Ikeda ◽  
Allan M. Lefer
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Cardiac Dysfunction ◽  
Ischemia Reperfusion ◽  
Left Ventricular ◽  
Polymorphonuclear Neutrophil ◽  
Caveolin 1 ◽  
Kinase C ◽  
Cardiac Contractile Dysfunction

Caveolin-1 is a protein constituent of cell membranes. The caveolin-1 scaffolding region (residues 82–101) is a known inhibitor of protein kinase C. Inhibition of protein kinase C results in maintained nitric oxide (NO) release from the endothelium, which attenuates cardiac dysfunction after ischemia-reperfusion (I/R). Therefore, we hypothesized that the caveolin-1 scaffolding region of the molecule, termed caveolin-1 peptide, might attenuate postischemia polymorphonuclear neutrophil (PMN)-induced cardiac dysfunction. We examined the effects of caveolin-1 peptide in isolated ischemic (20 min) and reperfused (45 min) rat hearts reperfused with PMNs. Caveolin-1 peptide (165 or 330 μg) given intravenously 1 h before I/R significantly attenuated postischemic PMN-induced cardiac dysfunction, as exemplified by left ventricular developed pressure (LVDP) ( P < 0.01) and the maximal rate of develped pressure (+dP/d t max) ( P < 0.01), compared with I/R hearts obtained from rats given 0.9% NaCl. In addition, caveolin-1 peptide significantly reduced cardiac PMN infiltration from 195 ± 5 PMNs/mm2 in untreated hearts to 103 ± 5 and 60 ± 5 PMNs/mm2 in hearts from 165 and 330 μg caveolin-1 peptide-treated rats, respectively ( P < 0.01). PMN adherence to the rat coronary vasculature was also significantly reduced in rats given either 165 or 330 μg caveolin-1 peptide compared with rats given 0.9% NaCl ( P < 0.01). Moreover, caveolin-1 peptide-treated rat aortas exhibited a 2.2-fold greater basal release of NO than vehicle-treated aortas ( P < 0.01), and this was inhibited by N G-nitro-l-arginine methyl ester. These results provide evidence that caveolin-1 peptide significantly attenuated PMN-induced post-I/R cardiac contractile dysfunction in the isolated perfused rat heart, probably via enhanced release of endothelium-derived NO.

Nitric oxide donor SIN-1 inhibits mammalian cardiac calcium current through cGMP-dependent protein kinase

1995 ◽  
Vol 268 (1) ◽  
pp. C45-C54 ◽  
Author(s):  
G. M. Wahler ◽  
S. J. Dollinger
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase ◽  
Calcium Current ◽  
Inhibitory Effect ◽  
Cardiac Cells ◽  
Nitric Oxide Donor ◽  
Dependent Protein Kinase ◽  
Cyclic Monophosphate ◽  
Cgmp Dependent Protein Kinase ◽  
Dependent Protein

The effect of the nitric oxide (NO) donor SIN-1 (3-morpholino-sydnonimine) on the calcium current (ICa) was examined in guinea pig ventricular myocytes. SIN-1 had little effect on basal ICa. After moderate stimulation of ICa with 10 nM isoproterenol (ISO), 10 microM SIN-1 caused either stimulation or inhibition of ICa; 100 microM SIN-1 consistently caused inhibition. SIN-1 (1-100 microM) inhibited ICa equally following considerable enhancement of ICa by either 1 microM ISO or 100 microM 3-isobutyl-1-methylxanthine, a nonspecific phosphodiesterase (PDE) inhibitor. SIN-1 (100 microM) also inhibited ICa equally following enhancement by either 10 microM pipette adenosine 3',5'-cyclic monophosphate (cAMP) or hydrolysis-resistant 8-bromo-cAMP. Thus the inhibitory effect of SIN-1 appears independent of PDEs. Addition of LY-83583 (a blocker of guanylate cyclase) to the pipette or superfusion with KT-5823 [a blocker of the guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase] suppressed the inhibitory effect of SIN-1. We conclude that NO is an important modulator of beta-adrenergic effects on ICa and that the mechanism of NO inhibition of ICa in mammalian cardiac cells involves the cGMP-dependent protein kinase.

scholarly journals Prolactin activation of mammary nitric oxide synthase: molecular mechanisms

2002 ◽  
Vol 28 (1) ◽  
pp. 45-51 ◽  
Author(s):  
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Molecular Mechanisms ◽  
Mammary Epithelial Cells ◽  
Calcium Ionophore ◽  
Mammary Epithelial ◽  
No Production ◽  
2B Protein ◽  
Oxide Synthase

Prolactin (PRL) is capable of stimulating both calcium and nitric oxide (NO) accumulation in mammary epithelial cells within 15min. A calcium ionophore was also able to stimulate NO levels to an extent similar to that generated by PRL. Furthermore, maximal concentrations of PRL and the ionophore were not additive, suggesting that they were both using the same pathway, i.e. calcium. Finally, the depletion of intracellular calcium completely abrogated the effect of PRL on NO production. No other pathway known to affect NO synthase (NOS) influenced the action of PRL. Specifically, manipulations of protein phosphatase 2B, protein kinase B (PKB), protein kinase C (PKC), and arginine transport did not alter the activation of NOS by PRL. Therefore, the ability of PRL to stimulate NO production at 15min can be completely explained by its ability to elevate intracellular calcium.

scholarly journals Aldose reductase modulates cardiac glycogen synthase kinase-3β phosphorylation during ischemia-reperfusion

2012 ◽  
Vol 303 (3) ◽  
pp. H297-H308 ◽  
Author(s):  
Mariane Abdillahi ◽  
Radha Ananthakrishnan ◽  
Srinivasan Vedantham ◽  
Linshan Shang ◽  
Zhengbin Zhu ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Aldose Reductase ◽  
Glycogen Synthase ◽  
Ischemia Reperfusion ◽  
Left Ventricular ◽  
Cardiac Cells ◽  
Glycogen Synthase Kinase ◽  
Glycogen Synthase Kinase 3Β ◽  
Apoptotic Markers ◽  
Ldh Release

Earlier studies have demonstrated that aldose reductase (AR) plays a key role in mediating ischemia-reperfusion (I/R) injury. Our objective was to investigate if AR mediates I/R injury by influencing phosphorylation of glycogen synthase kinase-3β (p-GSK3β). To investigate this issue, we used three separate models to study the effects of stress injury on the heart. Hearts isolated from wild-type (WT), human expressing AR transgenic (ARTg), and AR knockout (ARKO) mice were perfused with/without GSK3β inhibitors (SB-216763 and LiCl) and subjected to I/R. Ad-human AR (Ad-hAR)-expressing HL-1 cardiac cells were exposed to hypoxia (0.5% O2) and reoxygenation (20.9% O2) conditions. I/R in a murine model of transient occlusion and reperfusion of the left anterior descending coronary artery (LAD) was used to study if p-GSK3β was affected through increased AR flux. Lactate dehydrogenase (LDH) release and left ventricular developed pressure (LVDP) were measured. LVDP was decreased in hearts from ARTg mice compared with WT and ARKO after I/R, whereas LDH release and apoptotic markers were increased ( P < 0.05). p-GSK3β was decreased in ARTg hearts compared with WT and ARKO ( P < 0.05). In ARKO, p-GSK3β and apoptotic markers were decreased compared with WT ( P < 0.05). WT and ARTg hearts perfused with GSK3β inhibitors improved p-GSK3β expression and LVDP and exhibited decreased LDH release, apoptosis, and mitochondrial pore opening ( P < 0.05). Ad-hAR-expressing HL-1 cardiac cells, exposed to hypoxia (0.5% O2) and reoxygenation (20.9% O2), had greater LDH release compared with control HL-1 cells ( P < 0.05). p-GSK3β was decreased and correlated with increased apoptotic markers in Ad-hAR HL-1 cells ( P < 0.05). Treatment with phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) inhibitor increased injury demonstrated by increased LDH release in ARTg, WT, and ARKO hearts and in Ad-hAR-expressing HL-1 cells. Cells treated with protein kinase C (PKC) α/β inhibitor displayed significant increases in p-Akt and p-GSK3β expression, and resulted in decreased LDH release. In summary, AR mediates changes in p-GSK3β, in part, via PKCα/β and Akt during I/R.

Platelet activation by collagen is increased in retinal vein occlusion

2007 ◽  
Vol 97 (02) ◽  
pp. 218-227 ◽  
Author(s):  
Debora Bruzzese ◽  
Maria Signorello ◽  
Ugo Armani ◽  
Antonietta Piana ◽  
Davidina Ghiglione ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Retinal Vein Occlusion ◽  
Healthy Subjects ◽  
Platelet Response ◽  
Metabolic Characteristics ◽  
Vein Occlusion ◽  
Kinase C

SummaryRetinal vein occlusion (RVO) is the most common retinal vascular disorder second to diabetic retinopathy. The main risk factors in patients with RVO are hypertension, diabetes, hyperlipidemia, increased blood viscosity and glaucoma. The pathogenesis of RVO has not yet been clarified. In these events platelets could play a very important role. In the present study the platelet response to collagen was deeply investigated. Experiments were carried out on a selected group of RVO patients, which were compared to a group of healthy subjects matched for age, sex, clinical and metabolic characteristics. In resting and activated platelets of both groups of subjects p72syk phosphorylation, phospholipase Cγ 2 phosphorylation, protein kinase C activation, intracellular calcium levels and nitric oxide formation were measured. Results show that platelets of patients were more responsive to collagen or ADP than healthy subjects and that the response was significantly different (p < 0.0005) at low concentrations of these agonists. In platelets of patients stimulated with collagen increased phosphorylation of p72syk and phospholipase C γ 2 was found. Also protein kinase C was more activated in patients. In addition intracellular calcium rise induced by collagen was significantly higher in patients than in healthy subjects. RVO patients showed a lower basal level of nitric oxide both in resting and stimulated platelets compared to healthy subjects. Altogether these results suggest that the platelet hyperaggregability described in patients might be an important factor in the development of RVO contributing to the thrombogenic effects.

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