Endocardial endothelium in the rat: cell shape and organization of the cytoskeleton

Pericardial fluid of cardiac patients elicits arterial constriction: role of endothelin-1

Recently, several vasoactive molecules have been found in pericardial fluid (PF). Thus, we hypothesized that in coronary artery disease due to ischemia or ischemia-reperfusion, the level of vasoconstrictors, mainly endothelin-1 (ET-1), increases in PF, which can increase the vasomotor tone of arteries. Experiments were performed using an isometric myograph. Vasomotor effects of PF from patients undergoing coronary artery bypass graft (PFCABG, n = 14) or valve replacement (PFVR, n = 7) surgery were examined in isolated rat carotid arteries (N = 14; n = 26). Vasomotor responses to KCl (40 or 60 mmol/L) were also tested. The selective endothelin A receptor antagonist BQ123 (10(-6) mol/L) was used to elucidate the role of ET-1. Both the first and the second additions of KCl elicited increases in the isometric force of the isolated arteries (KCl1, 6.1 ± 0.2 mN; KCl2, 6.5 ± 0.9 mN). PFCABG and PFVR elicited substantial increases in the isometric force of arteries (PFCABG, 3.1 ± 0.7 mN; PFVR, 3.0 ± 0.9 mN; p > 0.05). The presence of the selective endothelin A receptor blocker significantly reduced arterial contractions to PFCABG (before BQ123, 2.6 ± 0.5 mN vs. after BQ123, 0.8 ± 0.1 mN; p < 0.05). This study is the first to demonstrate that PFs of patients elicit substantial arterial constrictions, which is mediated primarily by ET-1. Interfering with the vasoconstrictor action of PF could be a potential therapeutic target to improve coronary blood flow in cardiac patients.

ETS-dependent regulation of a distal Gata4 cardiac enhancer

The developing heart contains an inner tube of specialized endothelium known as endocardium, which performs multiple essential functions. In spite of the essential role of the endocardium in heart development and function, the transcriptional pathways that regulate its development remain largely undefined. GATA4 is a zinc finger transcription factor that is expressed in multiple cardiovascular lineages and is required for endocardial cushion development and embryonic viability, but the transcriptional pathways upstream of Gata4 in the endocardium and its derivatives in the endocardial cushions are unknown. Here, we describe a distal enhancer from the mouse Gata4 gene that is briefly active in multiple cardiac lineages early in cardiac development but restricts to the endocardium where it remains active through cardiogenesis. The activity of this Gata4 cardiac enhancer in transgenic embryos and in cultured aortic endothelial cells is dependent on four ETS sites. To identify which ETS transcription factors might be involved in Gata4 regulation via the ETS sites in the enhancer, we determined the expression profile of 24 distinct ETS factors in embryonic mouse hearts. Among multiple ETS transcripts present, ETS1, FLI1, ETV1, ETV5, ERG, and ETV6 were the most abundant in the early embryonic heart. We found that ETS1, FLI1, and ERG were strongly expressed in the heart at embryonic day 8.5 and that ETS1 and ERG bound to the endogenous Gata4 enhancer in cultured endothelial cells. Thus, these studies define the ETS expression profile in the early embryonic heart and identify an ETS-dependent enhancer from the Gata4 locus.

Distribution of NADPH-diaphorase and AChE activity in the anterior leaflet of rat mitral valve

The mitral valve, as an active flap, forms the major part of the left ventricular inflow tract and therefore plays an important function in many aspects of left ventricular performance. The anterior leaflet of this valve is the largest and most ventrally placed of two leaflets that come together during ventricular systole to close the left atrioventricular orifice. Various neurotransmitters are responsible for different functions including controlling valve movement, inhibiting or causing the failure of impulse conduction in the valve and the sensation of pain. Nitric oxide acts as a gaseous free radical neurotransmitter, neuromediator and effective cardiovascular modulator. Acetyl-choline is known to function as a typical neurotransmitter. Histochemical methods for detection of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), as an indirect nitric oxide-synthase marker, and method for detection of acetylcholinesterase (AChE) were used. Both methods were performed on the same valve sample. A widespread distribution of nerve fibres was observed in the anterior leaflet of the mitral valve. The fine NADPH-d positive (nitrergic) nerve fibres were identified in all zones of valve leaflet. AChE positive (cholinergic) nerve fibres were identified forming dense network and fibres organized in stripes. Endocardial cells and vessels manifested heavy NADPH-d activity. Our observations suggest a different arrangement of nitrergic and cholinergic nerve fibres in the anterior leaflet of the mitral valve. The presence of nitrergic and cholinergic activity confirms the involvement of both neurotransmitters in nerve plexuses and other structures of mitral valve.

Mitochondrial dysfunction and cytoskeletal disruption during chemical hypoxia to cultured rat hepatic sinusoidal endothelial cells: the pH paradox and cytoprotection by glucose, acidotic pH, and glycine

We investigated mechanisms underlying death of cultured rat liver sinusoidal endothelial cells exposed to chemical hypoxia with KCN (2.5 mmol/L) to simulate the adenosine triphosphate (ATP) depletion and reductive stress of anoxia. During chemical hypoxia, acidotic pH prevented cell death. Glucose (0.3-10 mmol/L) also prevented cell killing. Cytoprotection by glucose but not acidosis was associated with prevention of ATP depletion. After 4 hours of chemical hypoxia at pH 6.2 (simulated ischemia), rapid cell death occurred when pH was restored to pH 7.4 with or without washout of KCN (simulated reperfusion). This pH-dependent reperfusion injury (pH paradox) was prevented after KCN washout at pH 6.2. Glycine (0.3-3 mmol/L) also prevented the pH paradox, but glucose did not. The initial protection by acidotic pH and glycine during simulated reperfusion was lost when pH was later restored to 7.4 or glycine was subsequently removed. Mitochondria depolarized during chemical hypoxia. After washout of cyanide, mitochondrial membrane potential (delta psi) did not recover in cells that subsequently lost viability. Conversely, those cells that repolarized after cyanide washout did not subsequently lose viability. The actin cytoskeleton and focal adhesions became severely disrupted during chemical hypoxia at both pH 6.2 and 7.4 and did not recover after cyanide washout under any condition. Glucose during chemical hypoxia prevented cytoskeletal disruption. In conclusion, endothelial cell damage during simulated ischemia/reperfusion involves mitochondrial dysfunction, ATP depletion, and ATP-dependent cytoskeletal disruption. Glycine and acidotic pH prevented cell killing after reperfusion but did not reverse mitochondrial injury or the profound disruption to the cytoskeleton.

Nonuniformity of endothelial constitutive nitric oxide synthase distribution in cardiac endothelium

Endocardial endothelium and endothelium of coronary vessels produce NO. Histochemical methods have suggested that coronary arterial endothelial cells contain more endothelial constitutive NO synthase (ecNOS) than does coronary venous endothelium. We have further investigated the distribution of ecNOS in cardiac endothelium using immunofluorescence and en face confocal microscopy of rat heart. In endocardial endothelium, confocal microscopy revealed distinct ecNOS labeling of peripheral cell borders, cytoplasmic labeling, and labeling of the Golgi complexes. Labeling of the cell borders and of the Golgi complexes was confirmed by double staining for ecNOS and for platelet and endothelial cell adhesion molecule or Golgi 58k protein, respectively. Cytoplasmic labeling was strongest in coronary arterial endothelium. The size of the ecNOS-labeled Golgi complexes decreased from coronary arterial endothelial cells (8.63 +/- 0.39 microm2, mean +/- SE of 5 rats) to endocardial endothelium (7.07 +/- 0.61 microm2) and to coronary venous endothelium (3.65 +/- 0.20 microm2). In addition, pixel intensity of ecNOS labeling was higher in arterial endothelial cells than in venous endothelial cells. Endothelium of myocardial capillaries also contained small ecNOS-labeled Golgi complexes. No correlation was observed between endothelial cell surface area and Golgi complex size. Caveolin-1 labeling was strongest in capillaries and did not coincide completely with ecNOS labeling in endocardial and venous endothelium. These results suggest that endocardial and coronary arterial endothelium in the rat have a higher synthetic activity and might express more ecNOS than is expressed by cardiac venous and capillary endothelium. The observed heterogeneity in ecNOS distribution might be related to the specific mechanochemical environment and function of each endothelial compartment.

Evidence for the migration of rat aortic endothelial cells toward the heart

Most vascular endothelial cells at the edge of experimentally induced wounds have their centrosomes oriented toward the wound in the direction of cell migration. The finding that the centrosomes in endothelial cells of non-wounded aorta and vena cava are also oriented toward the heart suggested the hypothesis that endothelial cells are normally migrating in this direction. To test this hypothesis, endothelial cells in a segment of the rat abdominal aorta were labeled with a relatively nontoxic dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), and the position of the labeled cells was determined 3 and 6 weeks later. The results obtained showed that in 6 of the 9 rat aortas examined at 3 weeks and 15 of the 20 rat aortas examined at 6 weeks, DiI-labeled endothelial cells had migrated various distances up to 5000 microns toward the heart. In contrast, no migration of endothelial cells was detected at the opposite end of the labeled segment, in the direction away from the heart. These results demonstrate that vascular endothelial cells in the abdominal aorta of the rat are not stationary but are migrating toward the heart. The significance of the migration of endothelial cells toward the heart is presently unknown; however, it would be interesting to explore whether or not the impairment of this migration may contribute to disease processes in which the ability to maintain an intact and normally functioning endothelial cell lining is compromised as in atherosclerosis.

Oxidative stress-induced actin reorganization mediated by the p38 mitogen-activated protein kinase/heat shock protein 27 pathway in vascular endothelial cells

Vascular endothelial cells are constantly in contact with oxyradicals and must be especially well equipped to resist their toxic effects and generate appropriate physiological responses. Despite the importance of oxyradicals in the physiopathology of the vascular endothelium, the mechanisms regulating the oxidative response of endothelial cells are poorly understood. In the present study, we observed that H2O2 in concentrations that induced severe fragmentation of F-actin in fibroblasts rather induced a reorganization of F-actin in primary cultures of human umbilical vein endothelial cells (HUVECs) that was characterized by the accumulation of stress fibers, the recruitment of vinculin to focal adhesions, and the loss of membrane ruffles, H2O2 also induced in these cells a strong (10- to 14-fold) activation of the p38 mitogen-activated protein (MAP) kinase, which resulted in activation of MAP kinase-activated protein kinase-2/3 and phosphorylation of the F-actin polymerization modulator, heat shock protein 27 (HSP27). The MAP kinases extracellular-regulated kinase, and c-Jun N-terminal kinase/stress-activated protein kinase were only slightly increased by these treatments. Inhibiting p38 activity with the highly specific inhibitor SB203580 blocked the H2O2-induced endothelial microfilament responses. Moreover, fibroblasts acquired an endothelium-like SB203580-sensitive actin response when HSP27 concentration was increased by gene transfection to the same high level as found in HUVECs. The results indicate that activation of p38 MAP kinase in cells such as endothelial cells, which naturally express high level of HSP27, plays a central role in modulating microfilament responses to oxidative stress. Consequently, the p38 MAP kinase pathway may participate in the several oxyradical-activated functions of the endothelium that are associated with reorganization of microfilament network.

Endocardial endothelial dysfunction and heart failure

Like vascular endothelium, the EE plays a role in transendothelial transport, in coagulant and thrombotic processes, and in interactions with inflammatory cells. In addition, EE is involved in the modulation of cardiac performance of subjacent myocardium. EE dysfunction includes insufficient as well as excessive performance of any of its multiple functions. Dysfunction can progress from a disturbed modulation of myocardial performance and an imbalance in the release of growth factors to changes in EE cytoskeletal organization, with concomitant changes in transendothelial permeability, and in extreme cases, to loss of endothelial integrity and frank denudation. Structural and functional impairment of EE and of endocardial interstitial cells may be primary or secondary to the disease. Mechanical stress, various hormones and cytokines can initiate EE dysfunction. EE dysfunction may influence the development of cardiac failure in endo(myo)cardial fibrosis (Loeffler's endocarditis and carcinoid syndrome) and in dilated cardiomyopathy. Although Bouillaud, in 1836, was referring to endocarditis when stating: (quote: see text) his statement may presently find a much broader field of applicability in cardiology.

The cardiac endothelium: functional morphology, development, and physiology

Cardiac endothelial cells, regardless of whether they are from endocardial or from coronary (micro)vascular origin, directly modulate performance of the subjacent cardiomyocytes, resulting in control of the onset of ventricular relaxation and rapid filling of the heart. This review summarizes major features of the morphology, embryology, and comparative physiology of cardiac endothelial cells as well as the experimental observations on how cardiac endothelial cells affect the mechanical performance of the heart. As for the underlying mechanisms of the interaction between cardiac endothelial cells and cardiomyocytes, two working hypotheses have been postulated over the past years; (1) interaction mediated through a trans-endothelial physicochemical gradient for various ions (active blood-heart barrier), and (2) interaction mediated through the release by the cardiac endothelial cells of various cardioactive substances, eg, nitric oxide, endothelin, and prostacyclin. These two mechanisms may act in concert or in parallel.

The pathomorphological alterations of endocardial endothelium in experimental diabetes and diabetes associated with hyperlipidemia

The structural alterations of endocardial endothelial cells of the heart right atrium and left ventricle were investigated in Golden Syrian hamsters subjected to streptozotocin-induced diabetes and to a combination of diabetes and diet-induced hyperlipidemia. Animals were examined at time intervals ranging from 2 weeks to 6 months. Anionic sites of the endothelial plasmalemma were visualized by in situ perfusion of cationized ferritin. The results indicated that: (a) both atrial and ventricular endocardial endothelium are affected in streptozotocin-induced diabetes: endothelium converts from continuous into a fenestrated type, (b) although the anionic charge of the plasmalemma decreased in advanced diabetes, the newly formed fenestrae highly bound cationized ferritin, (c) combined diabetes and hyperlipidemia induced more severe alterations of endocardial endothelium: new permeable endothelial structures were formed (transendothelial channels, open intercellular junctions, fused plasmalemmal vesicles), and the cells became particularly enriched in cytoskeleton (intermediate filaments and microtubules), (d) the thick subendocardial layer of connective tissue contained, in the combined experimental model, macrophage derived foam cells indicative for the occurrence of alterations of atherosclerotic type.

Endothelin-mediated positive inotropic effect induced by reactive oxygen species in isolated cardiac muscle

Cardiac endothelium, both coronary and endocardial, produces a number of inotropic molecules. Changes in cardiac endothelial function by substances in the superfusing blood may thus participate in the control of muscle-pump performance of the heart. Reactive oxygen species (ROS) have been implicated in normal and pathological vascular physiology by influencing vascular endothelial function. Therefore, we examined the influence of ROS on endocardial endothelial modulation of myocardial performance. Right ventricular cat papillary muscles were briefly (15 s) exposed to electrolysis-generated ROS. Peak total isometric twitch tension and peak rate of tension development increased by 7.8 +/- 0.7% (P < .05) and 9.7 +/- 1.5% (P < .05), respectively (n = 12). Isometric twitch duration was slightly increased (time from stimulus to half isometric relaxation, +2.7 +/- 0.6%; P < .05). ROS scavengers such as ascorbic acid (n = 6), superoxide dismutase and catalase (n = 8), or catalase alone (n = 6), but not superoxide dismutase alone (n = 6), blocked the inotropic effect. Interestingly, the positive inotropic effect was completely blocked by selectively damaging endocardial endothelium (Triton X-100, 0.5%, 1-s immersion, n = 7) before ROS generation and by preincubating the muscles with the endothelin-A receptor antagonist BQ 123 (n = 11). Preincubation with NG-nitro-L-arginine methyl ester and indomethacin (n = 5) or with atenolol (n = 6) did not influence the inotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocardial endothelium in the rat: junctional organization and permeability

Selective permeability of endocardial endothelium has been suggested as a mechanism underlying the modulation of the performance of subjacent myocardium. In this study, we characterized the organization and permeability of junctional complexes in ventricular endocardial endothelium in rat heart. The length of intercellular clefts viewed en face per unit endothelial cell surface area was lower, and intercellular clefts were deeper in endocardial endothelium than in myocardial vascular endothelium, whereas tight junctions had a similar structure in both endothelia. On this basis, endocardial endothelium might be less permeable than capillary endothelium. However, confocal scanning laser microscopy showed that intravenously injected dextran 10,000 coupled to Lucifer Yellow penetrated first the endocardial endothelium and later the myocardial capillary endothelium. Penetration of dextran 10,000 in myocardium occurred earlier through subepicardial capillary endothelium than through subendocardial capillary endothelium. Penetration of tracer might thus be influenced by hydrostatic pressure. Dextran of MW 40,000 did not diffuse through either endocardial endothelium or capillary endothelium. The ultrastructure of endocardial endothelium may constitute an adaptation to limit diffusion driven by high hydrostatic pressure in the heart. Differences in paracellular diffusion of dextran 10,000, between endocardial endothelium and myocardial vessels, may result from differing permeability properties of the endocardium and underlying myocardium.