Nonuniformity of endothelial constitutive nitric oxide synthase distribution in cardiac endothelium

Manipulating angiogenesis in medicine

Blood vessels nourish organs with vital nutrients and oxygen and, thus, new vessels form when the embryo needs to grow or wounds are to heal. However, forming new blood vessels is a complex and delicate process, which, unfortunately, is often derailed. Thus, when insufficient vessels form, the tissue becomes ischaemic and stops to function adequately. Conversely, when vessels grow excessively, malignant and inflamed tissues grow faster. It is now becoming increasingly evident that abnormal vessel growth contributes to the pathogenesis of numerous malignant, ischaemic, inflammatory, infectious and immune disorders. With an in-depth molecular understanding, we should be better armamented to combat such angiogenic disorders in the future. That such therapeutic strategies might change the face of medicine is witnessed by initial evidence of success in the clinic.

A theoretical model of nitric oxide transport in arterioles: frequency- vs. amplitude-dependent control of cGMP formation

Nitric oxide (NO) plays many important physiological roles, including the regulation of vascular smooth muscle tone. In response to hemodynamic or agonist stimuli, endothelial cells produce NO, which can diffuse to smooth muscle where it activates soluble guanylate cyclase (sGC), leading to cGMP formation and smooth muscle relaxation. The close proximity of red blood cells suggests, however, that a significant amount of NO released will be scavenged by blood, and thus the issue of bioavailability of endothelium-derived NO to smooth muscle has been investigated experimentally and theoretically. We formulated a mathematical model for NO transport in an arteriole to test the hypothesis that transient, burst-like NO production can facilitate efficient NO delivery to smooth muscle and reduce NO scavenging by blood. The model simulations predict that 1) the endothelium can maintain a physiologically significant amount of NO in smooth muscle despite the presence of NO scavengers such as hemoglobin and myoglobin; 2) under certain conditions, transient NO release presents a more efficient way for activating sGC and it can increase cGMP formation severalfold; and 3) frequency-rather than amplitude-dependent control of cGMP formation is possible. This suggests that it is the frequency of NO bursts and perhaps the frequency of Ca(2+) oscillations in endothelial cells that may limit cGMP formation and regulate vascular tone. The proposed hypothesis suggests a new functional role for Ca(2+) oscillations in endothelial cells. Further experimentation is needed to test whether and under what conditions in silico predictions occur in vivo.

Localization of NOS-1 in the sarcolemma region of a subpopulation of atrial cardiomyocytes including myoendocrine cells and NOS-3 in vascular and endocardial endothelial cells of the rat heart

Cellular localization patterns of NOS isoforms 1 and 3 (nNOS and eNOS, respectively) in the mammalian heart under basal (non-stimulated) working conditions are still a matter of discussion. Therefore, this issue was reinvestigated in rats using RT-PCR, Western blotting, catalytic histochemistry, immunohistochemistry and image analysis. Tongue and extensor digitorum longus muscles served as positive controls for NOS-1 and NOS-3. RT-PCR revealed NOS-1 mRNA and NOS-3 mRNA in atria and ventricles. Western blotting showed NOS-1 protein in atria and NOS-3 protein in the walls of both heart chambers. Localization of the activity of urea-resistant (and therefore specific) NADPH diaphorase (NADPH-D) and NOS-1 immunohistochemistry showed that NOS-1 is present in the sarcolemma region of a subpopulation of atrial cardiomyocytes but not in working and impulse-conducting cardiomyocytes of atria and ventricles. Atrial natriuretic peptide (ANP) immunohistochemistry revealed that a minority of the NOS-1-expressing atrial cardiomyocytes are myoendocrine cells. eNOS immunostaining was present in endothelial cells of capillaries of the conducting and working myocardium and endocardial cells. Image analysis of the activity of urea-resistant NOS diaphorase showed that NOS-1 activity is lower in the sarcolemma region of atrial cardiomyocytes than in that of tongue and extensor digitorum longus myofibers. These data suggest that, in the non-stimulated rat heart. NOS-1 is expressed in a subpopulation of atrial cardiomyocytes including myoendocrine cells, and that NOS-3 is expressed in the vascular and endocardial endothelium.

Up-regulation of cardiac nitric oxide synthase 1-derived nitric oxide after myocardial infarction in senescent rats

Nitric oxide (NO) has been implicated in the development of heart failure, although the source, significance, and functional role of the different NO synthase (NOS) isoforms in this pathology are controversial. The presence of a neuronal-type NOS isoform (NOS1) in the cardiac sarcoplasmic reticulum has been recently discovered, leading to the hypothesis that NOS1-derived NO may notably alter myocardial inotropy. However, the regulation and role(s) of NOS1 in cardiac diseases remain to be determined. Using an experimental model of myocardial infarction (MI) in senescent rats, we demonstrated a significant increase in cardiac NOS1 expression and activity in MI, coupled with the translocation of this enzyme to the sarcolemma through interactions with caveolin-3. The enhanced NOS1 activity counteracts the decrease in cardiac NOS3 expression and activity observed in heart failure. We demonstrated an increased interaction between NOS1 and its regulatory protein HSP90 in post-MI hearts, a potential mechanism for the higher NOS1 activity in this setting. Finally, preferential in vivo inhibition of NOS1 activity enhanced basal post-MI left ventricular dysfunction in senescent rats. These results provide the first evidence that increased NOS1-derived NO production may play a significant role in the autocrine regulation of myocardial contractility after MI in aging rats.

Involvement of the proteasome in activation of endothelial nitric oxide synthase

Nitric oxide originating from the endothelial cells of the vessel wall is essential for the vascular system. It is produced by the enzyme endothelial nitric oxide synthase (eNOS). Cellular eNOS activity is affected by changes in eNOS synthesis. To address whether degradation also contributes to eNOS activity, the effect of proteasome inhibitors on eNOS-mediated NO synthesis was studied in the microvascular endothelial cell line bEnd.3 and in cultured primary aortic endothelial cells. Surprisingly, agonist-induced increases in eNOS activity were reduced to 42 and 50% in the presence of the proteasome inhibiting drugs MG132 and clasto-lactacystin-beta-lactone, respectively (P < 0.01). The decrease in activity occurred within 1 hour of drug treatment and was not accompanied by a change in intracellular levels of either eNOS or its inhibitor caveolin-1. Taken together, these data may indicate that eNOS is regulated by an interacting protein, different from caveolin-1, that inhibits its activity and is rapidly degraded by the proteasome in the presence of eNOS agonists.

NAD(P)H oxidase-generated superoxide anion accounts for reduced control of myocardial O2 consumption by NO in old Fischer 344 rats

We investigated the role of nitric oxide (NO) in the control of myocardial O2 consumption in Fischer 344 rats. In Fischer rats at 4, 14, and 23 mo of age, we examined cardiac function using echocardiography, the regulation of cardiac O2 consumption in vitro, endothelial NO synthase (eNOS) protein levels, and potential mechanisms that regulate superoxide. Aging was associated with a reduced ejection fraction [from 75 +/- 2% at 4 mo to 66 +/- 3% (P < 0.05) at 23 mo] and an increased cardiac diastolic volume [from 0.60 +/- 0.04 to 1.00 +/- 0.10 ml (P < 0.01)] and heart weight (from 0.70 +/- 0.02 to 0.90 +/- 0.02 g). The NO-mediated control of cardiac O2 consumption by bradykinin or enalaprilat was not different between 4 mo (36 +/- 2 or 34 +/- 3%) and 14 mo (29 +/- 1 or 25 +/- 3%) but markedly (P < 0.05) reduced in 23-mo-old Fischer rats (15 +/- 3 or 7 +/- 2%). The response to the NO donor S-nitroso-N-acetyl penicillamine was not different across groups (35%, 35%, and 44%). Interestingly, the eNOS protein level was not different at 4, 14, and 23 mo. The addition of tempol (1 mmol/l) to the tissue bath eliminated the depression in the control of cardiac O2 consumption by bradykinin (25 +/- 3%) or enalaprilat (28 +/- 3%) in 23-mo-old Fischer rats. We next examined the levels of enzymes involved in the production and breakdown of superoxide. The expression of Mn SOD, Cu/Zn SOD, extracellular SOD, and p67phox, however, did not differ between 4- and 23-mo-old rats. Importantly, there was a marked increase in gp91phox, and apocynin restored the defect in NO-dependent control of cardiac O2 consumption at 23 mo to that seen in 4-mo-old rats, identifying the role of NADPH oxidase. Thus increased biological activity of superoxide and not decreases in the enzyme that produces NO are responsible for the altered control of cardiac O2 consumption by NO in 23-mo-old Fischer rats. Increased oxidant stress in aging, by decreasing NO bioavailability, may contribute not only to changes in myocardial function but also to altered regulation of vascular tone and the progression of cardiac or vascular disease.

Pericardium of the frog, Rana esculenta, is morphologically designed as a lymphatic space

The importance of the pericardium and the pericardial fluid (PF) in the control of cardiac function has emerged over the past few years. Despite the acknowledgment that amphibians are exposed to both dehydration and excessive water accumulation, nothing is known about their pericardial structure and the morphological basis of the PF formation. We have studied the parietal pericardium (PP) morphology in Rana esculenta by electron microscopy. SEM images of the inner surface, which lines the pericardial cavity, revealed the presence of large vesicles and many small circular openings. TEM observations showed that the PP is made up of an inner mesothelial lining, often constituted by two layers of very flat cells lying on a basal membrane and of regularly oriented collagen bundles. The PP outer surface is lined by a layer of flat cells, without a basal membrane. The mesothelial cells had overlapping boundaries with complex intercellular connections and a rich pool of caveolae opened in the direction of both the pericardial cavity and intercellular spaces. These cells indicate an intense intracellular and/or intercellular transfer of fluids and substances. The intraperitoneal injection of the idromineral hormone, Val(5)-ANG II, induced PP modifications, particularly evident at the level of the structures involved in the transmesothelial traffic. These lymphatic-like traits suggest that the frog PP represents a large lymphatic sac, subject to paracrine-endocrine remodeling, which can actively adjust the PF, influencing the composition and volume of the myocardial interstitial fluid.

Regulation of endothelial nitric oxide synthase by the actin cytoskeleton

In the present study, the association of endothelial nitric oxide synthase (eNOS) with the actin cytoskeleton in pulmonary artery endothelial cells (PAEC) was examined. We found that the protein contents of eNOS, actin, and caveolin-1 were significantly higher in the caveolar fraction of plasma membranes than in the noncaveolar fraction of plasma membranes in PAEC. Immunoprecipitation of eNOS from lysates of caveolar fractions of plasma membranes in PAEC resulted in the coprecipitation of actin, and immunoprecipitation of actin from lysates of caveolar fractions resulted in the coprecipitation of eNOS. Confocal microscopy of PAEC, in which eNOS was labeled with fluorescein, F-actin was labeled with Texas red-phalloidin, and G-actin was labeled with deoxyribonuclease I conjugated with Texas red, also demonstrated an association between eNOS and F-actin or G-actin. Incubation of purified eNOS with purified F-actin and G-actin resulted in an increase in eNOS activity. The increase in eNOS activity caused by G-actin was much higher than that caused by F-actin. Incubation of PAEC with swinholide A, an actin filament disruptor, resulted in an increase in eNOS activity, eNOS protein content, and association of eNOS with G-actin and in a decrease in the association of eNOS with F-actin. The increase in eNOS activity was higher than that in eNOS protein content in swinholide A-treated cells. In contrast, exposure of PAEC to phalloidin, an actin filament stabilizer, caused decreases in eNOS activity and association of eNOS with G-actin and increases in association of eNOS with F-actin. These results suggest that eNOS is associated with actin in PAEC and that actin and its polymerization state play an important role in the regulation of eNOS activity.

Influence of coronary artery diameter on eNOS protein content

The purpose of this study was to test the hypothesis that the content of endothelial nitric oxide synthase (eNOS) protein (eNOS protein/g total artery protein) increases with decreasing artery diameter in the coronary arterial tree. Content of eNOS protein was determined in porcine coronary arteries with immunoblot analysis. Arteries were isolated in six size categories from each heart: large arteries [301- to 2,500-microm internal diameter (ID)], small arteries (201- to 300-microm ID), resistance arteries (151- to 200-microm ID), large arterioles (101- to 150-microm ID), intermediate arterioles (51- to 100-microm ID), and small arterioles(<50-microm ID). To obtain sufficient protein for analysis from small- and intermediate-sized arterioles, five to seven arterioles 1-2 mm in length were pooled into one sample for each animal. Results establish that the number of smooth muscle cells per endothelial cell decreases from a number of 10 to 15 in large coronary arteries to 1 in the smallest arterioles. Immunohistochemistry revealed that eNOS is located only in endothelial cells in all sizes of coronary artery and in coronary capillaries. Contrary to our hypothesis, eNOS protein content did not increase with decreasing size of coronary artery. Indeed, the smallest coronary arterioles had less eNOS protein per gram of total protein than the large coronary arteries. These results indicate that eNOS protein content is greater in the endothelial cells of conduit arteries, resistance arteries, and large arterioles than in small coronary arterioles.

Endothelial cell heterogeneity

OBJECTIVE

To review recent advances in the field of endothelial cell heterogeneity, and to apply this knowledge to an understanding of site-specific vasculopathy, including acute lung injury.

DATA SOURCES AND STUDY SELECTION

Published research and review articles in the English language related to endothelial cell biology and endothelial cell heterogeneity.

DATA EXTRACTION AND SYNTHESIS

The results of published studies have been used to provide a perspective of endothelial cell phenotypes in health and disease.

CONCLUSIONS

The structure and function of endothelial cells are differentially regulated in space and time. Far from being a giant monopoly of homogeneous cells, the endothelium represents a consortium of smaller enterprises of cells located within blood vessels of different tissues. Although united in certain functions, each enterprise is uniquely adapted to meet the demands of the underlying tissue. The endothelium may also vary in its response to pathophysiologic stimuli and therefore contribute to the focal nature of vasculopathic disease states. In acute lung injury, the unique properties of the endothelium may conspire with systemic imbalances to localize pathology to the pulmonary vasculature.

The L-arginine-nitric oxide pathway in hypertension

Nitric oxide is involved in the regulation of resting vascular tone, adaptation of blood flow to metabolic demand of tissue, and adaptation of vessel diameter to volume of inflow, ie, flow-mediated dilation. Arterial hypertension is associated with an increased vascular tone of resistance vessels, a reduced compliance of conduit arteries, along with a thickening of the intima-media leading to vascular remodeling. Dysfunctional endothelium triggers such maladaptive processes. A reduced bioavailability of nitric oxide has been shown in hypertensive individuals dependent on the duration and severity of arterial hypertension. Angiotensin-converting enzyme inhibitors reverse endothelial dysfunction, whereas a concomitant reduction in significant cardiac events due to improved bioavailability has yet to be established. Long-term follow-up studies in individuals with manifest endothelial dysfunction and in offspring from hypertensive patients underscore the prognostic and genetic significance of a reduced nitric oxide bioavailability for the pathophysiology of arterial hypertension.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Molecular mechanisms involved in the regulation of the endothelial nitric oxide synthase

The endothelial nitric oxide synthase (eNOS), the expression of which is regulated by a range of transcriptional and posttranscriptional mechanisms, generates nitric oxide (NO) in response to a number of stimuli. The physiologically most important determinants for the continuous generation of NO and thus the regulation of local blood flow are fluid shear stress and pulsatile stretch. Although eNOS activity is coupled to changes in endothelial cell Ca(2+) levels, an increase in Ca(2+) alone is not sufficient to affect enzyme activity because the binding of calmodulin (CaM) and the flow of electrons from the reductase to the oxygenase domain of the enzyme is dependent on protein phosphorylation and dephosphorylation. Two amino acids seem to be particularly important in regulating eNOS activity and these are a serine residue in the reductase domain (Ser(1177)) and a threonine residue (Thr(495)) located within the CaM-binding domain. Simultaneous alterations in the phosphorylation of Ser(1177) and Thr(495) in response to a variety of stimuli are regulated by a number of kinases and phosphatases that continuously associate with and dissociate from the eNOS signaling complex. eNOS associated proteins, such as caveolin, heat shock protein 90, eNOS interacting protein, and possibly also motor proteins provide the scaffold for the formation of the protein complex as well as its intracellular localization.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

NOSTRIN: a protein modulating nitric oxide release and subcellular distribution of endothelial nitric oxide synthase

Activity and localization of endothelial nitric oxide synthase (eNOS) is regulated in a remarkably complex fashion, yet the complex molecular machinery mastering stimulus-induced eNOS translocation and trafficking is poorly understood. In a search by the yeast two-hybrid system using the eNOS oxygenase domain as bait, we have identified a previously uncharacterized eNOS-interacting protein, dubbed NOSTRIN (for eNOS traffic inducer). NOSTRIN contains a single polypeptide chain of 506-aa residues of 58 kDa with an N-terminal cdc15 domain and a C-terminal SH3 domain. NOSTRIN mRNA is abundant in highly vascularized tissues such as placenta, kidney, lung, and heart, and NOSTRIN protein is expressed in vascular endothelial cells. Coimmunoprecipitation experiments demonstrated the eNOS-NOSTRIN interaction in vitro and in vivo, and NOSTRIN's SH3 domain was essential and sufficient for eNOS binding. NOSTRIN colocalized extensively with eNOS at the plasma membrane of confluent human umbilical venous endothelial cells and in punctate cytosolic structures of CHO-eNOS cells. NOSTRIN overexpression induced a profound redistribution of eNOS from the plasma membrane to vesicle-like structures matching the NOSTRIN pattern and at the same time led to a significant inhibition of NO release. We conclude that NOSTRIN contributes to the intricate protein network controlling activity, trafficking, and targeting of eNOS.

ACh-induced endothelial NO synthase translocation, NO release and vasodilatation in the hamster microcirculation in vivo

Studies in cultured cells show that activation of endothelial nitric oxide (NO) synthase (eNOS) requires the dissociation of this enzyme from its inhibitory association with caveolin-1 (Cav-1), and perhaps its translocation from plasma membrane caveolae to other cellular compartments. We investigated the hypothesis that in vivo NO-dependent vasodilatation is associated with the translocation of eNOS from the cell membrane. To this end, we applied ACh topically (10-100 microM for 10 min) to the hamster cheek pouch microcirculation and measured NO production, blood flow and vessel diameter, and assessed subcellular eNOS distribution by Western blotting. Baseline NO production was 54.4 +/- 5.2 pmol min(-1) (n = 16). ACh increased NO release, caused arteriolar and venular dilatation and elevated microvascular flow. These responses were inhibited by N(G)-nitro-L-arginine (30 microM). The maximal increase in NO production induced by 10 microM and 100 microM ACh was 45 +/- 20 % and 111 +/- 33 %, respectively; the corresponding blood flow increases were 50 +/- 10 % and 130 +/- 24 %, respectively (n = 4-6). Both responses followed a similar time course, although increases in NO preceded flow changes. In non-stimulated tissues, eNOS was distributed mainly in the microsomal fraction. ACh-induced vasodilatation was associated with eNOS translocation to the cytosolic and Golgi-enriched fractions. After 1.5, 3.0 or 6.0 min of application, 10 microM ACh decreased the level of membrane-bound eNOS by -13 +/- 4 %, -60 +/- 4 % and -19 +/- 17 %, respectively; at the same time points, 100 microM ACh reduced microsomal eNOS content by -38 +/- 9 %, -61 +/- 16 % and -40 +/- 18 %, respectively (n = 4-5). In all cases, microsomal Cav-1 content did not change. The close ACh concentration dependence and the concomitance between eNOS subcellular redistribution and NO release support the concept that eNOS translocation from the plasma membrane is part of an activation mechanism that induces NO-dependent vasodilatation in vivo.

Inhibitory effect of glucocorticoid on coronary artery endothelial function

Acute and chronic stresses are implicated in cardiovascular diseases including coronary artery disease. The present study was designed to examine the direct effects of the stress hormone cortisol on nitric oxide (NO) release and endothelial NO synthase (eNOS) expression in cultured bovine coronary artery endothelial cells (BCAEC). Nitrate, nitrite, and NO (NO(x)) were measured by the chemiluminescence method. At 24 h after treatment, cortisol (1 nM-10 microM) produced a dose-dependent decrease in NO(x) release, which was attenuated in the presence of the 11beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone (3 microM). In accordance, eNOS protein levels were significantly decreased by cortisol in a dose-dependent manner. Cortisol pretreatment significantly increased the rate of eNOS protein degradation in the presence of cycloheximide. In addition, cortisol pretreatment decreased ATP-induced intracellular Ca(2+) elevation and NO(x) release in BCAEC. The presence of glucocorticoid receptors in BCAEC was demonstrated by Western blot. The results suggest that cortisol, through activation of glucocorticoid receptors, suppresses NO(x) release in BCAEC by downregulating eNOS proteins and inhibiting intracellular Ca(2+) mobilization. Decreased NO(x) is likely to result in an increase in contraction of coronary arteries, leading to a decrease in coronary blood flow.

The nitric oxide synthase-1 and nitric oxide synthase-3/nitric oxide signalling systems in the heart of wild type mice and mouse mutants

Recently, we have shown that nitric oxide synthase-1 (NOS-1) and thus its product NO are present in the sarcolemma region of a subpopulation of atrial cardiomyocytes in the rat heart. In order to find out whether this newly discovered sarcolemma-associated NOS/NO system represents a general signalling mechanism in the murine rodent heart and whether its properties are comparable to those in skeletal muscle fibres, immunohistochemical and catalytic histochemical methods (including image analysis) were applied to the heart and extensor digitorum longus (EDL) and tongue muscles of wild type and mutant mice. In different strains of wild type mice and NOS-3 knockouts, urea-resistant (and therefore specific) NOS NADPH diaphorase histochemistry and NOS-1 immunohistochemistry revealed that NOS-1 activity and protein were present in the sarcolemma region of a subpopulation of atrial and ventricular working cardiomyocytes, but not in those of the impulse conducting system. Using image analysis, NOS-1 showed similar activities in the sarcolemma region of cardiomyocytes and in EDL type I myofibres. In mdx and NOS-1 knockout mice, NOS-1 was absent from the sarcolemma region of atrial and ventricular cardiomyocytes and of EDL and tongue muscle fibres, whereas NOS-1 was present in the hearts of NOS-3 knockouts. Atrial natriuretic peptide immunohistochemistry identified part of the atrial NOS-1-expressing cardiomyocytes as myoendocrine cells. In mdx mice as well as in NOS-1 - and NOS-3-deficient animals, the peptide was found in greater abundance than in wild type mice. These data suggest that NOS-1 is expressed in a subpopulation of working cardiomyocytes in the murine rodent heart, that the myoendocrine cells may be negatively modulated by NOS-1 - and NOS-3-produced NO, and that the anchoring mechanisms for NOS-1 in these cells (i.e. their confinement to the sarcolemma region) are comparable to those in skeletal muscle fibres.

Advances towards understanding heart valve response to injury

BACKGROUND

Composed of endocardial endothelial, valvular interstitial, cardiac muscle, and smooth muscle cells (SMC), heart valves are prone to various pathologic conditions the morphology of which has been well described. The morphology of diseased valves suggest that the "response to injury" process occurs in these valves, and is associated with an accumulation of interstitial cells and matrix, valvular inflammation and calcification, conditions that lead to dysfunction. The purpose of this study is to describe the current knowledge of the regulation of the valvular "response to injury" process, since we feel that this paradigm is essential to understanding valve disease.

METHODS

The pertinent literature relating to the cell and molecular biology of valvular repair, and specifically interstitial cell function in valve repair, is reviewed.

RESULTS

The cell and molecular biology of valve interstitial cells are poorly understood. Molecules regulating some of the aspects of the "response to injury" process have been studied, however, the signal transduction pathways, gene activation, and interactions of bioactive molecules with each other, with cells, and with the matrix have not been characterized. Initial studies identify the cell and molecular biology of interstitial cells to be an important area of research. Agents that have been studied include nitric oxide (NO) and FGF-2 and several matrix-related proteins including osteopontin. The present review suggests several directions for future study and a working model of valvular repair is presented.

DISCUSSION

The regulation of the "response to injury" process in the human heart valve is still largely unknown. The cell and molecular events and processes that occur in heart valve function and repair remain poorly understood. These events and processes are vital to our understanding of the pathobiology of heart valve disease, and to the successful design of tissue engineered replacement valves.

Endothelial nitric oxide synthase activity is linked to its presence at cell-cell contacts

The enzyme endothelial nitric oxide synthase (eNOS) is essential for vascular integrity. Many studies have demonstrated a link between the localization and activity of eNOS. Here, we studied the influence of cell-cell contact on this link in the microvascular endothelial bEnd.3 cell line. By immunofluorescence microscopy, eNOS localization at the plasma membrane was found to be dependent on cell-cell contact. In particular, eNOS was highly enriched at the intercellular contact sites. Further analysis showed that the pattern of eNOS localization at the plasma membrane resembled that of PECAM-1 (platelet endothelial cell adhesion molecule 1), but not that of the adherens junction proteins VE (vascular endothelial)-cadherin and plakoglobin. eNOS that was localized at the contact sites was, in part, Triton X-100-insoluble, in contrast with eNOS at the Golgi complex, which may indicate an association of eNOS with the actin cytoskeleton. Interestingly, eNOS activity was up-regulated in confluent monolayers compared with subconfluent cells, while there was no difference in eNOS expression. This correlation between cell confluence and eNOS activity was also found when primary bovine aortic endothelial cells were studied. These data imply that cell-cell contact induces the localization of eNOS at intercellular junctions, which is required for agonist-induced eNOS activation.

The nitric oxide pathway is amplified in venular vs arteriolar cultured rat mesenteric endothelial cells

To determine if there are differences in nitric oxide activity between pre- and postcapillary microvessels, we studied cultured rat mesenteric arteriolar and venular endothelial cells (RMAEC, RMVEC). We measured expression of endothelial nitric oxide synthase (eNOS), the activity of eNOS, and L-arginine transport in live RMAEC and RMVEC and the L-arginine content of RMAEC and RMVEC lysates. The abundance of eNOS was significantly greater in RMVEC vs RMAEC; this was also true for freshly harvested, pooled microvessels. Baseline NOS activity was higher in RMVEC than in RMAEC. NG-monomethyl-L-arginine (L-NMA; 5 mM) inhibited NOS activity by approximately 70-80% in both RMAEC and RMVEC, indicating that metabolism of l-arginine is largely via NOS. Intracellular L-arginine levels were higher in RMVEC vs RMAEC and well above the eNOS Km in both cell types. L-arginine levels increased with L-NMA in both RMAEC and RMVEC, presumably due to reduced substrate utilization. Since L-arginine transport was not higher in RMVEC vs RMAEC, this may reflect higher intracellular arginine synthesis. A higher intrinsic level of baseline NO production in the postcapillary microvascular endothelium may reflect both the contribution of venular derived NO to control of arteriolar tone and a key role of venular-derived NO in local thrombosis control.

Endogenous nitric oxide enhances coupling between O2 consumption and ATP synthesis in guinea pig hearts

Endogenous nitric oxide (eNO) modulates tissue respiration. To test whether eNO modulates myocardial O2 consumption (MVO2), ATP synthesis, and metabolic efficiency, we used isolated isovolumic guinea pig hearts perfused at a constant flow. N(omega)-nitro-L-arginine (L-NNA; 5 x 10(-5) mol/l) was used to inhibit eNO production. MVO2 was measured at different levels of cardiac work, estimated as the rate-pressure product (RPP). ATP content and synthesis rate were determined using (31)P NMR and magnetization transfer during high cardiac work. L-NNA increased coronary vascular resistance (19 +/- 3%, P < 0.05) and MVO2 (12 +/- 3%, P < 0.05) without an increase in the RPP. In contrast, vehicle infusion resulted in insignificant changes in coronary vascular resistance (3 +/- 2%, P > 0.05) and MVO2 (-2 +/- 1%, P > 0.05). Compared with vehicle, L-NNA caused a higher MVO2 both during KCl arrest (L-NNA 5.6 +/- 0.5 vs. vehicle 3.0 +/- 0.4 micromol x min(-1) x mg x dry wt(-1), P < 0.05) and during increased cardiac work elicited by elevating perfusate Ca2+, indicating an upward shift in the relationship between contractile performance (measured as RPP) and MVO2. However, neither ATP contents nor ATP synthesis rates were different in the two groups during high cardiac work. Thus, because inhibition of eNO production by L-NNA increased MVO2 without a change in the ATP synthesis rate, these data suggest that eNO increases myocardial metabolic efficiency by reducing MVO2 in the heart.

Regulation of hepatic eNOS by caveolin and calmodulin after bile duct ligation in rats

In carbon tetrachloride-induced liver cirrhosis, diminution of hepatic endothelial nitric oxide synthase (eNOS) activity may contribute to impaired hepatic vasodilation and portal hypertension. The mechanisms responsible for these events remain unknown; however, a role for the NOS-associated proteins caveolin and calmodulin has been postulated. The purpose of this study is to characterize the expression and cellular localization of the NOS inhibitory protein caveolin-1 in normal rat liver and to then examine the role of caveolin in conjunction with calmodulin in regulation of NOS activity in cholestatic portal hypertension. In normal liver, caveolin protein is expressed preferentially in nonparenchymal cells compared with hepatocytes as assessed by Western blot analysis of isolated cell preparations. Additionally, within the nonparenchymal cell populations, caveolin expression is detected within both liver endothelial cells and hepatic stellate cells. Next, studies were performed 4 wk after bile duct ligation (BDL), a model of portal hypertension characterized by prominent cholestasis, as evidenced by a significant increase in serum cholesterol in BDL animals. After BDL, caveolin protein levels from detergent-soluble liver lysates are significantly increased as assessed by Western blot analysis. Immunoperoxidase staining demonstrates that this increase is most prominent within sinusoids and venules. Additionally, caveolin-1 upregulation is associated with a significant reduction in NOS catalytic activity in BDL liver lysates, an event that is corrected with provision of excess calmodulin, a protein that competitively binds eNOS from caveolin. We conclude that, in cholestatic portal hypertension, caveolin may negatively regulate NOS activity in a manner that is reversible by excess calmodulin.

Can modulation of endothelial nitric oxide synthase explain the vasculoprotective actions of statins?

Statin-based drugs are the mainstay of therapy for coronary artery disease. Recent insights into the cellular mechanisms of this class of drugs suggest that modulation of nitric oxide synthesis contributes to their beneficial actions. These effects are independent of their lipid-lowering effects and result in enhanced nitric oxide release.

Direct interaction between endothelial nitric-oxide synthase and dynamin-2. Implications for nitric-oxide synthase function

Endothelial nitric-oxide synthase (eNOS) is regulated in part through specific protein interactions. Dynamin-2 is a large GTPase residing within similar membrane compartments as eNOS. Here we show that dynamin-2 binds directly with eNOS thereby augmenting eNOS activity. Double label confocal immunofluorescence demonstrates colocalization of eNOS and dynamin in both Clone 9 cells cotransfected with green fluorescent protein-dynamin and eNOS, as well as in bovine aortic endothelial cells (BAEC) expressing both proteins endogenously, predominantly in a Golgi membrane distribution. Immunoprecipitation of eNOS from BAEC lysate coprecipitates dynamin and, conversely, immunoprecipitation of dynamin coprecipitates eNOS. Additionally, the calcium ionophore, a reagent that promotes nitric oxide release, enhances coprecipitation of dynamin with eNOS in BAEC, suggesting the interaction between the proteins can be regulated by intracellular signals. In vitro studies demonstrate that glutathione S-transferase (GST)-dynamin-2 quantitatively precipitates both purified recombinant eNOS protein as well as in vitro transcribed (35)S-labeled eNOS from solution indicating a direct interaction between the proteins in vitro. Scatchard analysis of binding studies demonstrates an equilibrium dissociation constant (K(d)) of 27.6 nm. Incubation of purified recombinant eNOS protein with GST-dynamin-2 significantly increases eNOS activity as does overexpression of dynamin-2 in ECV 304 cells stably transfected with eNOS-green fluorescent protein. These studies demonstrate a direct protein-protein interaction between eNOS and dynamin-2, thereby identifying a new NOS-associated protein and providing a novel function for dynamin. These events may have relevance for eNOS regulation and trafficking within vascular endothelium.

Cellular regulation of endothelial nitric oxide synthase

Renal function is highly dependent on endothelium-derived nitric oxide (NO). Several renal disorders have been linked to impaired NO bioavailability. The enzyme that is responsible for the synthesis of NO within the renal endothelium is endothelial NO synthase (eNOS). eNOS-mediated NO generation is a highly regulated cellular event, which is induced by calcium-mobilizing agonists and fluid shear stress. eNOS activity is regulated at the transcriptional level but also by a variety of modifications, such as acylation and phosphorylation, by its cellular localization, and by protein-protein interactions. The present review focuses on the complex regulation of eNOS within the endothelial cell.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Chronic hypoxia increases the NO contribution of acetylcholine vasodilation of the fetal guinea pig heart

To investigate the effect of chronic hypoxia (HPX) on vasodilation of the fetal heart, we exposed pregnant guinea pigs to room air or 12% O(2) for 4, 7, or 10 days. We excised hearts from anesthetized fetuses (60 +/- 3 days; 65-day gestation = term) and measured changes in both the coronary artery pressure of the isolated constant-flow preparation and endothelial nitric oxide synthase (eNOS) mRNA of fetal ventricles. Dilator responses to cumulative addition (10(-9)-10(-5) M) of acetylcholine and sodium nitroprusside in prostaglandin F(2alpha) (5 x 10(-6) M)-constricted hearts were similar among normoxia (NMX), 4-, 7-, and 10-day HPX (control). Nitro-L-arginine (L-NA, 10(-4)M), a NOS inhibitor, inhibited maximal acetylcholine dilation of hearts exposed to 10-day HPX greater than NMX, 4-, and 7-day HPX. Hypoxia (after 7 and 10 days) increased eNOS mRNA of fetal ventricles compared with NMX and 4-day HPX. 4-Aminopyridine (3 mM), a voltage-dependent K(+)-channel inhibitor, inhibited acetylcholine- but not sodium nitroprusside-induced dilation of NMX and 10-day HPX hearts to a similar magnitude. Glibenclamide (10(-5) M), an ATP-sensitive K(+)-channel inhibitor, had no effect on vasodilation. We conclude that chronic HPX increases the contribution of NO but does not alter K(+)-channel activation in response to acetylcholine-stimulated coronary dilation. Thus increases in NO production via upregulation of eNOS gene expression may be an adaptive response to chronic HPX in the fetal coronary circulation.

Selective transport of adenosine into porcine coronary smooth muscle

Adenosine (ADO), an endogenous regulator of coronary vascular tone, enhances vasorelaxation in the presence of nucleoside transport inhibitors such as dipyridamole. We tested the hypothesis that coronary smooth muscle (CSM) contains a high-affinity transporter for ADO. ADO-mediated relaxation of isolated large and small porcine coronary artery rings was enhanced 12-fold and 3.4-fold, respectively, by the transport inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI). Enhanced relaxation was independent of endothelium and was selective for ADO over synthetic analogs. Uptake of [(3)H]ADO into freshly dissociated CSM cells or endothelium-denuded rings was linear and concentration dependent. Kinetic analysis yielded a maximum uptake (V(max)) of 67 +/- 7.0 pmol. mg protein(-1). min(-1) and a Michaelis constant (K(m)) of 10. 5 +/- 5.8 microM in isolated cells and a V(max) of 5.1 +/- 0.5 pmol. min(-1). mg wet wt(-1) and a K(m) of 17.6 +/- 2.6 microM in intact rings. NBTI inhibited transport into small arteries (IC(50) = 42 nM) and cells. Analyses of extracellular space and diffusion kinetics using [(3)H]sucrose indicate the V(max) and K(m) for ADO transport are sufficient to clear a significant amount of extracellular adenosine. These data indicate CSM possess a high-affinity nucleoside transporter and that the activity of this transporter is sufficient to modulate ADO sensitivity of large and small coronary arteries.

Quantification of eNOS mRNA in the canine cardiac vasculature by competitive PCR

The goal of the present study was to develop a competitive PCR assay to measure changes in the expression of endothelial nitric oxide synthase (eNOS) mRNA levels throughout the canine vascular tree. A partial sequence of canine eNOS cDNA (1.86 kb), inducible NOS (1.95 kb), and neuronal NOS (1.16 kb) was cultured from canine aortic endothelial cells, LPS-treated canine splenic vein endothelial cells, and from canine left ventricle, respectively. Competitor eNOS cDNA (eNOS-C) was constructed via recombinant PCR. Thus, with the use of a standard curve competitive PCR with eNOS-C, the amount of eNOS mRNA in 500 ng of total RNA was greatest in the circumflex > right coronary artery > left anterior descending coronary artery > aorta. The isolation of coronary microvessels from the left ventricle was associated with an enrichment of endothelial cell markers such as eNOS, von Willebrand factor, and caveolin-1, an observation supported by the detection of up to 15-fold higher levels of eNOS mRNA in coronary microvessels relative to the larger arteries. The ability to quantify changes in eNOS mRNA levels throughout the canine vasculature should provide greater insight into the molecular mechanisms of how this gene is regulated in physiological and pathophysiological states.

Phosphorylation and activation of the endothelial nitric oxide synthase by fluid shear stress

Fluid shear stress activates the endothelial nitric oxide (NO) synthase (eNOS) by a mechanism which does not require an increase in the intracellular concentration of free Ca2+ ([Ca2+]i), and is sensitive to several kinase inhibitors. Although phosphorylation of eNOS has been suggested to regulate enzyme activity, the mechanism of eNOS activation is still unclear. Here we demonstrate that fluid shear stress elicits the phosphorylation of eNOS on tyrosine and serine residues. Inhibition of phosphatidylinositol 3-kinase (PI3K), using wortmannin or a dominant negative mutant of its downstream target, Akt (protein kinase B), prevented the maintained serine phosphorylation and activation of eNOS. Enhancing eNOS phosphorylation by inhibiting serine/threonine phosphatases, increased eNOS activity by approximately twofold, as assessed by the accumulation of intracellular cyclic GMP, without increasing the intracellular concentration of free Ca2+. These data suggest that shear stress activates a pathway involving PI3K and the serine/threonine kinase Akt, which phosphorylates eNOS. This phosphorylation directly increases eNOS activity at resting [Ca2+]i, thus rendering the shear stress-induced activation of eNOS apparently Ca2+-independent.

Codistribution of NOS and caveolin throughout peripheral vasculature and skeletal muscle of hamsters

In isolated cell systems, nitric oxide synthase (NOS) activity is regulated by caveolin (CAV), a resident caveolae coat protein. Because little is known of this interaction in vivo, we tested whether NOS and caveolin are distributed together in the intact organism. Using immunohistochemistry, we investigated the localization of constitutive neuronal (nNOS) and endothelial (eNOS) enzyme isoforms along with caveolin-1 (CAV-1) and caveolin-3 (CAV-3) throughout the systemic vasculature and peripheral tissues of the hamster. The carotid artery, abdominal aorta, vena cava, femoral artery and vein, feed artery and collecting vein of the cheek pouch retractor muscle, capillaries and muscle fibers of retractor and cremaster muscles, and arterioles and venules of the cheek pouch were studied. In endothelial cells, eNOS and CAV-1 were present throughout the vasculature, whereas nNOS and CAV-3 were absent except in capillaries, which reacted for nNOS. In smooth muscle cells, nNOS and CAV-1 were also expressed systemically, whereas eNOS was absent; CAV-3 was present in the arterial but not the venous vasculature. Both nNOS and CAV-3 were located at the sarcolemma of skeletal muscle fibers, which were devoid of eNOS and CAV-1. These immunolabeling patterns suggest functional interactions between eNOS and CAV-1 throughout the endothelium, regional differences in the modulation of nNOS by caveolin isoforms in vascular smooth muscle, and modulation of nNOS by CAV-3 in skeletal muscle.

Trafficking of endothelial nitric-oxide synthase in living cells. Quantitative evidence supporting the role of palmitoylation as a kinetic trapping mechanism limiting membrane diffusion

To examine endothelial nitric-oxide synthase (eNOS) trafficking in living endothelial cells, the eNOS-deficient endothelial cell line ECV304 was stably transfected with an eNOS-green fluorescent protein (GFP) fusion construct and characterized by functional, biochemical, and microscopic analysis. eNOS-GFP was colocalized with Golgi and plasma membrane markers and produced NO in response to agonist challenge. Localization in the plasma membrane was dependent on the palmitoylation state, since the palmitoylation mutant of eNOS (C15S/C26S eNOS-GFP) was excluded from the plasma membrane and was concentrated in a diffuse perinuclear pattern. Fluorescence recovery after photobleaching (FRAP) revealed eNOS-GFP in the perinuclear region moving 3 times faster than the plasmalemmal pool, suggesting that protein-lipid or protein-protein interactions are different in these two cellular domains. FRAP of the palmitoylation mutant was two times faster than that of wild-type eNOS-GFP, indicating that palmitoylation was influencing the rate of trafficking. Interestingly, FRAP of C15S/C26S eNOS-GFP but not wild-type eNOS-GFP fit a model of protein diffusion in a lipid bilayer. These data suggest that the regulation of eNOS trafficking within the plasma membrane and Golgi are probably different mechanisms and not due to simple diffusion of the protein in a lipid bilayer.

Expression and regulation of the sodium-calcium exchanger in cardiac microvascular endothelial cells

1. The sodium-calcium exchanger (NCX) plays an important role in Ca2+ homeostasis. In the heart, NCX participates in the control of contraction and relaxation and in large vessel endothelial cells some data suggest that NCX could influence nitric oxide (NO) generation. In this context, the cardiac microvasculature has received considerable attention as a mediator of myocardial performance, via the release of paracrine acting factors such as NO. Therefore, the aim of the current study was to characterize NCX expression and regulation in cardiac microvascular endothelial cells (CMEC). The NCX expression was also examined in neonatal ventricular cardiomyocytes where aspects of its function and regulation have been well characterized. 2. The presence of functional NCX in CMEC was confirmed by the presence of a consistent rise in intracellular Ca2+ concentration ([Ca2+]i) in response to removal of extracellular Na+. Furthermore, NCX mRNA expression was readily detectable in CMEC. 3. In order to examine the role of possible physiological regulators of NCX expression, the effect of intracellular Ca2+ loading, caused by 24 h exposure to 10 mumol/L ouabain, was investigated. In Ca(2+)-loaded CMEC, there was a substantially greater rise in [Ca2+]i during exposure to Na(+)-free buffer: 33 +/- 6 versus 124 +/- 25 nmol/L% (P < 0.05), consistent with increased protein expression. Consistent with these findings, northern blot analysis confirmed the presence of a two-fold increase in NCX mRNA in these cells. 4. These data indicate the presence of functional NCX in CMEC and identify [Ca2+]i as a potential physiological regulator of expression.

Cardiac microvascular endothelial cells express alpha-smooth muscle actin and show low NOS III activity

We established a culture system of porcine coronary microvascular endothelial cells (MVEC) with high cellular yield and purity >98%. Endothelial origin was confirmed by immunostaining, immunoblotting and fluorescence-activated cell sorter (FACS) analysis using low-density lipoprotein uptake, CD31, von Willebrand factor, and the lectin Dolichos biflorus agglutinin. MVEC were positive for alpha-smooth muscle actin in culture and in myocardium, as confirmed by FACS. Of the primary MVEC, approximately 30% expressed nitric oxide synthase (NOS) III in numbers decreasing from the first passage (6 +/- 1%) to the second passage (4 +/- 1%; P < 0.001 vs. primary isolates), whereas approximately 100% of aortic endothelial cells (AEC) expressed NOS III. In AEC, NOS III activity (pmol citrulline. mg protein-1. min-1) was 80 +/- 10 and was nearly abolished in the absence of calcium (5 +/- 1, P < 0.001). In primary MVEC, however, NOS III activity in the presence and absence of calcium was 20 +/- 4 and 25 +/- 5, respectively. We conclude that cardiac MVEC, in contrast to AEC, contain alpha-smooth muscle actin, show low-grade NOS III activity, and provide a suitable in vitro system for the study of endothelial pathophysiology.

Estradiol induces the calcium-dependent translocation of endothelial nitric oxide synthase

Although estrogen is known to stimulate nitric oxide synthesis in vascular endothelium, the molecular mechanisms responsible for this effect remain to be elucidated. Using quantitative immunofluorescence imaging approaches, we have investigated the effect of estradiol on the subcellular targeting of endothelial nitric oxide synthase (eNOS) in bovine aortic endothelial cells. In unstimulated endothelial cells, eNOS is predominantly localized at the cell membrane. Within 5 min after the addition of estradiol, most of the eNOS translocates from the membrane to intracellular sites close to the nucleus. On more prolonged exposure to estradiol, most of the eNOS returns to the membrane. This effect of estradiol is evident at a concentration of 1 pM, and a maximal estradiol effect is seen at a concentration of 1 nM. Neither progesterone nor testosterone has any effect on eNOS distribution. After estradiol addition, a transient rise in intracellular Ca2+ concentration precedes eNOS translocation. Both the Ca2+-mobilizing and eNOS-translocating effects of estradiol are completely blocked by the estrogen receptor antagonist ICI 182,780, and the intracellular Ca2+ chelator 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) prevents estradiol-induced eNOS translocation. Use of the nitric oxide-specific dye diaminofluorescein shows that estradiol treatment increases nitric oxide generation by endothelial cells; this response is blocked by ICI 182,780 and by the eNOS inhibitor Nomega-nitro-L-arginine. These results show that estradiol induces subcellular translocation of eNOS by a rapid, Ca2+-dependent, receptor-mediated mechanism, and they suggest a nongenomic role for estrogen in the modulation of NO-dependent vascular tone.

Isometric contraction induces the Ca2+-independent activation of the endothelial nitric oxide synthase

Shear stress and tyrosine phosphatase inhibitors have been shown to activate the endothelial NO synthase (eNOS) in a Ca2+/calmodulin-independent manner. We report here that isometric contraction of rabbit aorta activates eNOS by a pharmacologically identical pathway. Endothelium-intact aortic rings were precontracted under isometric conditions up to 60% of the maximal phenylephrine-induced tone. The NO synthase inhibitor NGnitro-L-arginine (L-NA) and the soluble guanylyl cyclase inhibitor NS 2028 induced an additional contraction, the amplitude of which depended on the level of precontraction. The maximal production of NO by isometrically contracted aortic rings (as estimated by the increase in cGMP in detector smooth muscle cells in a superfusion bioassay) was observed during the initial phase of isometric contraction and was greater than that detected following the application of acetylcholine. The supplementary L-NA-induced increase in vascular tone was inhibited by the nonselective kinase inhibitor staurosporine and the tyrosine kinase inhibitors erbstatin A and herbimycin A. Another tyrosine kinase inhibitor, genistein, the calmodulin antagonist calmidazolium, and the selective protein kinase C inhibitor, Ro 31-8220, had no effect. Coincident with the enhanced NO formation during isometric contraction was an increase in the tyrosine phosphorylation of endothelial proteins, which also correlated with the level of precontraction. Thus, isometric contraction activates eNOS via a Ca2+-independent, tyrosine kinase inhibitor-sensitive pathway and, like shear stress, seems to be an independent determinant of mechanically induced NO formation.