Vasoactive amines modulate actin cables (stress fibers) and surface area in cultured bovine endothelium

Mast Cell Histamine-Induced Calcium Transients in Cultured Human Peritoneal Mesothelial Cells

Objective

Peritoneal inflammation results from a complex interplay of events initiated by macrophage activity in response to infection, with the stimulation of mesothelial cell cytokine release amplifying the recruitment of blood-borne defense cells to the site of injury. Resident peritoneal mast cells may add to this complexity with mast cell derived cytokines released during this cascade. This study examined the influence of histamine, a mast cell derived inflammatory mediator, on the initial activation of human peritoneal mesothelial cells (HPMC) by intracellular free calcium (Cai2+) mobilization, and changes to the actin cytoskeleton.

Design

HPMC signal transduction was examined in response to histamine (1.0 mmol/L) compared to fetal bovine serum (FBS) (0.1 %) and 4-br-A23187 (1.0 μmol/L). Intracellular free calcium was measured in fura-2 loaded cells with and without external calcium (Ca2ex+t), or Ca2ex+t with verapamil (100 μmol/L). Following treatment with agonists, HPMC actin cytoskeleton was stained using direct immunocytochemistry.

Results

HPMC responded to histamine with a twofold transient rise in Cai2+ which returned to the baseline, in contrast with FBS and A23187–induced Cai2+ transients, which returned to elevated resting values. In the absence of Ca2ex+t’ all agents produced a calcium transient indicative of calcium release from intracellular stores. Histamine induced calcium -dependent changes to the cytoskeleton and cellular organization, including increased actin stress fibers.

Conclusion

Histamine produced large specific receptor-mediated calcium transients in HPMC, which included components of calcium release from intracellular stores and receptor -mediated calcium influx processes. The observed response to histamine raises the possibility that histamine derived from resident mast cells may modulate mesothelial cell function, in part by calciumdependent pathways, and influence the performance of the peritoneal membrane during peritoneal dialysis.

The Effects of Serotonin in Immune Cells

Serotonin [5-hydroxytryptamine (5-HT)] plays an important role in many organs as a peripheral hormone. Most of the body’s serotonin is circulating in the bloodstream, transported by blood platelets and is released upon activation. The functions of serotonin are mediated by members of the 7 known mammalian serotonin receptor subtype classes (15 known subtypes), the serotonin transporter (SERT), and by covalent binding of serotonin to different effector proteins. Almost all immune cells express at least one serotonin component. In recent years, a number of immunoregulatory functions have been ascribed to serotonin. In monocytes/macrophages, for example, serotonin modulates cytokine secretion. Serotonin can also suppress the release of tumor necrosis factor-α and interleukin-1β by activating serotonin receptors. Furthermore, neutrophil recruitment and T-cell activation can both be mediated by serotonin. These are only a few of the known immunomodulatory roles of serotonin that we will review here.

Histamine activates p38 MAP kinase and alters local lamellipodia dynamics, reducing endothelial barrier integrity and eliciting central movement of actin fibers

The role of the actin cytoskeleton in endothelial barrier function has been debated for nearly four decades. Our previous investigation revealed spontaneous local lamellipodia in confluent endothelial monolayers that appear to increase overlap at intercellular junctions. We tested the hypothesis that the barrier-disrupting agent histamine would reduce local lamellipodia protrusions and investigated the potential involvement of p38 mitogen-activated protein (MAP) kinase activation and actin stress fiber formation. Confluent monolayers of human umbilical vein endothelial cells (HUVEC) expressing green fluorescent protein-actin were studied using time-lapse fluorescence microscopy. The protrusion and withdrawal characteristics of local lamellipodia were assessed before and after addition of histamine. Changes in barrier function were determined using electrical cell-substrate impedance sensing. Histamine initially decreased barrier function, lamellipodia protrusion frequency, and lamellipodia protrusion distance. A longer time for lamellipodia withdrawal and reduced withdrawal distance and velocity accompanied barrier recovery. After barrier recovery, a significant number of cortical fibers migrated centrally, eventually resembling actin stress fibers. The p38 MAP kinase inhibitor SB203580 attenuated the histamine-induced decreases in barrier function and lamellipodia protrusion frequency. SB203580 also inhibited the histamine-induced decreases in withdrawal distance and velocity, and the subsequent actin fiber migration. These data suggest that histamine can reduce local lamellipodia protrusion activity through activation of p38 MAP kinase. The findings also suggest that local lamellipodia have a role in maintaining endothelial barrier integrity. Furthermore, we provide evidence that actin stress fiber formation may be a reaction to, rather than a cause of, reduced endothelial barrier integrity.

Propranolol treatment of infantile hemangioma endothelial cells: A molecular analysis

Infantile hemangiomas (IHs) are non-malignant, largely cutaneous vascular tumors affecting approximately 5-10% of children to varying degrees. During the first year of life, these tumors are strongly proliferative, reaching an average size ranging from 2 to 20 cm. These lesions subsequently stabilize, undergo a spontaneous slow involution and are fully regressed by 5 to 10 years of age. Systemic treatment of infants with the non-selective β-adrenergic receptor blocker, propranolol, has demonstrated remarkable efficacy in reducing the size and appearance of IHs. However, the mechanism by which this occurs is largely unknown. In this study, we sought to understand the molecular mechanisms underlying the effectiveness of β blocker treatment in IHs. Our data reveal that propranolol treatment of IH endothelial cells, as well as a panel of normal primary endothelial cells, blocks endothelial cell proliferation, migration, and formation of the actin cytoskeleton coincident with alterations in vascular endothelial growth factor receptor-2 (VEGFR-2), p38 and cofilin signaling. Moreover, propranolol induces major alterations in the protein levels of key cyclins and cyclin-dependent kinase inhibitors, and modulates global gene expression patterns with a particular affect on genes involved in lipid/sterol metabolism, cell cycle regulation, angiogenesis and ubiquitination. Interestingly, the effects of propranolol were endothelial cell-type independent, affecting the properties of IH endothelial cells at similar levels to that observed in neonatal dermal microvascular and coronary artery endothelial cells. This data suggests that while propranolol markedly inhibits hemangioma and normal endothelial cell function, its lack of endothelial cell specificity hints that the efficacy of this drug in the treatment of IHs may be more complex than simply blockage of endothelial function as previously believed.

Real-time monitoring of morphological changes in living cells by electronic cell sensor arrays: an approach to study G protein-coupled receptors

G protein-coupled receptors (GPCRs) constitute important targets for drug discovery against a wide range of ailments including cancer, inflammatory, and cardiovascular diseases. Efforts are underway to screen selective modulators of GPCRs and also to deorphanize GPCRs with unidentified natural ligands. Most GPCR-based cellular screens depend on labeling or recombinant expression of receptor or reporter proteins, which may not capture the true physiology or pharmacology of the GPCRs. In this paper, we describe a noninvasive and label-free assay for GPCRs that can be used with both engineered and nonengineered cell lines. The assay is based on using cell-electrode impedance to measure minute changes in cellular morphology as a result of ligand-dependent GPCR activation. We have used this technology to assay the functional activation of GPCRs coupled to different signaling pathways and have compared it to standard assays. We have used pharmacological modulators of GPCR signaling pathways to demonstrate the specificity of impedance-based measurements. Our data indicate that cell-electrode impedance measurements offer a convenient, sensitive, and quantitative method for assessing GPCR function. Moreover, the noninvasive nature of the readout offers the added advantage of performing multiple treatments in the same well to study events such as desensitization and receptor cross-talk.

Extracellular matrix, junctional integrity and matrix metalloproteinase interactions in endothelial permeability regulation

Vascular endothelial permeability is maintained by the regulated apposition of adherens and tight junctional proteins whose organization is controlled by several pharmacological and physiological mediators. Endothelial permeability changes are associated with: (1) the spatial redistribution of surface cadherins and occludin, (2) stabilization of focal adhesive bonds and (3) the progressive activation of matrix metalloproteinases (MMPs). In response to peroxide, histamine and EDTA, endothelial cells sequester VE-cadherin and alter its cytoskeletal binding. Simultaneously, these mediators enhance focal adhesion to the substratum. Oxidants, cytokines and pharmacological mediators also trigger the activation of matrix metalloproteinases (MMPs) in a cytoskeleton and tyrosine phosphorylation dependent manner to degrade occludin, a well-characterized tight junction element. These related in vitro phenomena appear to co-operate during inflammation, to increase endothelial permeability, structurally stabilize cells while also remodelling cell junctions and substratum.

Modern views on an ancient chemical: serotonin effects on cell proliferation, maturation, and apoptosis

Evolutionarily, serotonin existed in plants even before the appearance of animals. Indeed, serotonin may be tied to the evolution of life itself, particularly through the role of tryptophan, its precursor molecule. Tryptophan is an indole-based, essential amino acid which is unique in its light-absorbing properties. In plants, tryptophan-based compounds capture light energy for use in metabolism of glucose and the generation of oxygen and reduced cofactors. Tryptophan, oxygen, and reduced cofactors combine to form serotonin. Serotonin-like molecules direct the growth of light-capturing structures towards the source of light. This morphogenic property also occurs in animal cells, in which serotonin alters the cytoskeleton of cells and thus influences the formation of contacts. In addition, serotonin regulates cell proliferation, migration and maturation in a variety of cell types, including lung, kidney, endothelial cells, mast cells, neurons and astrocytes). In brain, serotonin has interactions with seven families of receptors, numbering at least 14 distinct proteins. Of these, two receptors are important for the purposes of this review. These are the 5-HT1A and 5-HT2A receptors, which in fact have opposing functions in a variety of cellular and behavioral processes. The 5-HT1A receptor develops early in the CNS and is associated with secretion of S-100beta from astrocytes and reduction of c-AMP levels in neurons. These actions provide intracellular stability for the cytoskeleton and result in cell differentiation and cessation of proliferation. Clinically, 5-HT1A receptor drugs decrease brain activity and act as anxiolytics. The 5-HT2A receptor develops more slowly and is associated with glycogenolysis in astrocytes and increased Ca(++) availability in neurons. These actions destabilize the internal cytoskeleton and result in cell proliferation, synaptogenesis, and apoptosis. In humans, 5-HT2A receptor drugs produce hallucinations. The dynamic interactions between the 5-HT1A and 5-HT2A receptors and the cytoskeleton may provide important insights into the etiology of brain disorders and provide novel strategies for their treatment.

Protein phosphorylation in the blood-brain barrier. Possible presence of MARCKS in brain microvessels

The protein phosphorylation in rat brain microvessels has been examined; the major phosphorylated proteins correspond to a doublet of molecular weight 134-141 kDa, and four proteins of approx. 25, 55, 80 and 200 kDa. TPA (12-O-tetradecanoylphorbol-13-acetate) enhanced, in a few minutes, the phosphorylation of three major protein substrates with apparent molecular weights of 17.5, 44.5 and 80 kDa. These effects are inhibited by staurosporine. The 80 kDa protein resulted to be myristoylated alanine-rich C kinase substrate (MARCKS). This work demonstrates that protein kinase C plays an important role in protein phosphorylation in blood-brain barrier (BBB).

Serotonin regulates mouse cranial neural crest migration

Serotonergic agents (uptake inhibitors, receptor ligands) cause significant craniofacial malformations in cultured mouse embryos suggesting that 5-hydroxytryptamine (serotonin) (5-HT) may be an important regulator of craniofacial development. To determine whether serotonergic regulation of cell migration might underly some of these effects, cranial neural crest (NC) explants from embryonic day 9 (E9) (plug day = E1) mouse embryos or dissociated mandibular mesenchyme cells (derived from NC) from E12 embryos were placed in a modified Boyden chamber to measure effects of serotonergic agents on cell migration. A dose-dependent effect of 5-HT on the migration of highly motile cranial NC cells was demonstrated, such that low concentrations of 5-HT stimulated migration, whereas this effect was progressively lost as the dose of 5-HT was increased. In contrast, most concentrations of 5-HT inhibited migration of less motile, mandibular mesenchyme cells. To investigate the possible involvement of specific 5-HT receptors in the stimulation of NC migration, several 5-HT subtype-selective antagonists were used to block the effects of the most stimulatory dose of 5-HT (0.01 microM). Only NAN-190 (a 5-HT1A antagonist) inhibited the effect of 5-HT, suggesting involvement of this receptor. Further evidence was obtained by using immunohistochemistry with 5-HT receptor antibodies, which revealed expression of the 5-HT1A receptor but not other subtypes by migrating NC cells in both embryos and cranial NC explants. These results suggest that by activating appropriate receptors 5-HT may regulate migration of cranial NC cells and their mesenchymal derivatives in the mouse embryo.

Modulation of endothelial cell permeability by lung carcinoma cells: a potential mechanism of malignant pleural effusion formation

This study examined the hypothesis that tumor cells metastatic to the pleura secrete a soluble factor(s) that directly increases endothelial cell permeability. Nitrocellulose filters were endothelialized with bovine pulmonary artery endothelial cells and exposed to conditioned media from either human lung adenocarcinoma (Calu-3), human lung squamous cell carcinoma (SK-MES-1), or control media for 16 h. The diffusional permeability (Pd x 10(-5) cm/sec) to [14C]albumin was then determined for each monolayer with Ussing-type chambers. Both adenocarcinoma conditioned media (ACCM) and squamous cell carcinoma conditioned media (SCCM) caused a two- to threefold increase in endothelial monolayer permeability. The addition of indomethacin (10 micrograms/ml) blocked the observed permeability increase in ACCM but not in SCCM, suggesting that the increase in permeability by ACCM was secondary to the production of prostaglandins. To confirm this, a variety of prostanoids previously shown to be produced by the Calu-3 cell line were added directly to the endothelial monolayer. Prostaglandin F2 alpha (PGF2 alpha) in both low (10 ng/ml) and high (100 ng/ml) concentrations for 16 h resulted in a three- to fourfold increase in permeability. Prostaglandin E2 (PGE2) resulted in a small increase in [14C]albumin permeability but only at high concentrations (100 ng/ml). PGF2 alpha production by the two tumor cell lines was measured using radioimmunoassay. Baseline adenocarcinoma production of PGF2 alpha was 117.5 pmol/10(6) cells and fell to 24.2 pmol/10(6) cells hours following incubation with indomethacin. The decrease in PGF2 alpha occurred in parallel with the changes in permeability. Concomitant, reversible changes in cell shape and F-actin distribution were detected in endothelial cells exposed to ACCM. No significant production of PGF2 alpha by the squamous cell carcinoma cell line was detected. These results suggest that both adenocarcinoma and squamous cell carcinoma secrete a soluble factor(s) that directly increases endothelial cell permeability to albumin and that in the case of adenocarcinoma this soluble factor may be a prostanoid such as PGF2 alpha.

What intracranial tissues in humans contain sumatriptan-sensitive serotonin 5-HT1-type receptors?

We investigated the presence of sumatriptan-sensitive serotonin (5-HT)1 receptors in different human tissues by using a radioligand-binding technique with [3H]5-HT. Sumatriptan displaced [3H]5-HT from frontal cortical and striatal membranes in a biphasic manner, with a high-affinity site corresponding to binding to the 5-HT1D receptor. In blood platelet membranes, sumatriptan displaced [3H]5-HT with a 100-fold lower affinity. Sumatriptan failed to displace [3H]5-HT in membranes from large cerebral arteries, pial vessels, coronary arteries and dura mater. These findings suggest that either there are no sumatriptan-sensitive 5-HT1 receptors on intracranial blood vessels or they are so small in number that they cannot be detected by the radioligand-binding technique. Other mechanisms, possibly centrally mediated, may be responsible for the antimigraine action of sumatriptan.

An N-cadherin-like protein contributes to solute barrier maintenance in cultured endothelium

We investigated the role of cadherins in the solute barrier maintained by endothelial cells in vitro. Cell-column chromatographic measurement of endothelial barrier showed that reducing normal extracellular calcium from 1.2 to 0.12 mM increased endothelial permeability to 250% of baseline after 20 min. Restoring normal calcium restored the barrier within 15 min which remained stable for at least 60 min. We used sulfo-NHS-biotin and anti-cadherin antibodies to characterize endothelial proteins with possible roles in the maintenance of endothelial barrier. The non-specific probe sulfo-NHS-biotin identified at least ten endothelial cell surface proteins, with greatest labelling occurring at molecular weights of 125 and 145 kD. Six proteins, including the 125 and 145 kD proteins, associated with the cytoskeleton. Western blotting for the presence of classical cadherins containing the conserved cytoplasmic sequence CDPTAPPYDSLLVFDYEG detected two bands at 145 and 125 kD which associated with the cytoskeleton. Western blotting with an antibody, which recognizes FHLRAHAVDINGNQV, an extracellular homotypic binding region of N-cadherin, detects three bands. Of these three, one protein had a molecular weight of 125 kD and was associated with the cytoskeleton. Immunofluorescence with both N-cadherin and anti-peptide 1 antibodies found staining at endothelial cell borders. The utility of a newly developed cell-column calcium switch assay was tested by verifying the functional role of the previously described epithelial cadherin, uvomorulin, in epithelial barrier. We then applied this method to endothelial cell columns and found the N-cadherin antibody interfered with the reforming of interendothelial junctions. These results suggest that, as in epithelial cells, cadherins in bovine endothelial cells have a functional role in forming the calcium sensitive endothelial junction and may play an important role in the formation of normal barrier.

Serotonin and cardiac morphogenesis in the mouse embryo

The possible involvement of the neurotransmitter serotonin (5-HT) and its binding protein (SBP) in cardiac morphogenesis was studied using mouse whole embryo culture (together with immunocytochemistry or 3H-thymidine autoradiography) and a cell migration assay. Embryos were cultured before and during the period of endocardial cushion formation, embryonic (E) days 9-12, in the presence of 5-HT, the monoamine oxidase (MAO) inhibitor nialamide, or an uptake inhibitor (fluoxetine or sertraline). For the migration assay, cells from the outflow tracts of E12 embryos were dissociated and placed in a chemotaxis chamber together with different concentrations of 5-HT. E9 embryos cultured in the presence of 10 microM 5-HT and nialamide exhibited intense 5-HT immunoreactivity (5-HT IR) throughout the myocardium. This staining was greatly diminished by fluoxetine, sertraline, or the absence of nialamide. As morphogenesis proceeded, myocardial staining in embryos exposed to 5-HT became restricted to developing endocardial cushion forming regions and was more completely blocked by uptake inhibitors. No evidence for 5-HT synthesis by myocardium was found at any age studied using the precursor L-tryptophan. SBP was present in endocardial cushions in cultured and uncultured embryos. 3H-thymidine autoradiography demonstrated that both fluoxetine and sertraline inhibited proliferation of cardiac mesenchyme, endocardium, and myocardium. These effects were most pronounced when exposure began at E9 (prior to cushion formation). Dose-dependent effects of 5-HT on migration of outflow tract cells were also observed. Taken together, these results suggest that 5-HT may play a role in cardiac morphogenesis during endocardial cushion formation.

Immunolocalization of cytokeratin 19 in bovine and human pulmonary microvascular endothelial cells in situ

1. Immunocytochemical analysis of bovine and human lung sections revealed the presence of the 41 kD intermediate filament protein cytokeratin 19 in microvessel and subpleural lymphatic endothelial cells as well as the mesothelial cell layer of the lung visceral pleura. 2. Cytokeratin 19 was expressed by human and bovine pulmonary microvessels with diameters ranging from 5 to 50 microns. 3. Cytokeratin 19 was also found in microvessels of the rete mirabile, an oxygen exchange organ of the eel. 4. Immunoperoxidase electron microscopy demonstrated cytokeratin 19 associated with the lateral membranes of adjacent bovine alveolar capillary endothelial cells.

Thrombin and histamine rapidly stimulate the phosphorylation of the myristoylated alanine-rich C-kinase substrate in human umbilical vein endothelial cells: evidence for distinct patterns of protein kinase activation

Human alpha-thrombin and histamine each stimulates protein phosphorylation in human umbilical vein endothelial cells (HUVEC). We have identified the most prominent of these phosphoproteins by immunoprecipitation as the human homolog of the widely distributed myristoylated alanine-rich C-kinase substrate (MARCKS). Stimulation by 0.1-10 U/ml of alpha-thrombin produces a time-dependent, sustained (plateau 3-5 min) level of MARCKS phosphorylation. MARCKS phosphorylation requires thrombin catalytic activity but not receptor binding and is also seen in response to stimulation by a peptide, TR (42-55), that duplicates a portion of the thrombin receptor tethered ligand created by thrombin proteolytic activity. One micromolar histamine, like alpha-thrombin, produces sustained phosphorylation of MARCKS (plateau 3-5 min). In contrast, 100 microM histamine results in rapid but transient MARCKS phosphorylation (peak 1-3 min). HUVEC treated with 100 microM histamine for 5 min can be restimulated by alpha-thrombin but not fresh histamine, suggesting that the histamine receptor was desensitized. MARCKS phosphorylation can also be induced by several exogenous protein kinase C (PKC) activators and both alpha-thrombin- and histamine-induced MARCKS phosphorylation are inhibited by the PKC antagonist staurosporine. However, while prolonged PMA pretreatment ablates histamine-induced MARCKS phosphorylation, the ability of thrombin to induce MARCKS phosphorylation is retained. These findings provide evidence for agonist-specific pathways of protein kinase activation in response to thrombin and histamine in HUVEC.

Thrombolytic therapy causes an increase in vascular permeability that is reversed by 1-deamino-8-D-vasopressin

BACKGROUND

To examine the effect of plasminogen activator therapy on vascular permeability, we used a modified rabbit mesenteric model of extravascular tissue accumulation of radiolabeled albumin.

METHODS AND RESULTS

Albumin deposition was measured after saline, tissue-type plasminogen activator (t-PA; 0.86 mg/kg for 1 hour followed by 0.29 mg/kg for 2 hours), or t-PA plus 1-deamino-8-D-arginine vasopressin (DDAVP; 0.6 mg/kg/hr for 30 minutes) infusion in animals with or without aspirin (ASA; 15-mg/kg bolus) pretreatment. In animals not given ASA, t-PA caused a 240% increase in tissue [125I]albumin accumulation over time (p less than 0.001). DDAVP prevented the rise in albumin accumulation normally seen with t-PA alone (p less than 0.05) in animals not given ASA. In animals pretreated with ASA, t-PA similarly caused an increase in tissue albumin accumulation, but this was significantly attenuated from that of animals not given ASA (p less than 0.03). Interestingly, DDAVP failed to block the response to t-PA in the animals given ASA. Because increases in vascular permeability correlated with increases in bleeding time (r = 0.37, p less than 0.03), these data suggest that the effect of plasmin generation on vascular permeability may contribute to the bleeding tendency seen with thrombolytic therapy. The ability of DDAVP to reverse the bleeding tendency and bleeding time may be due in part to its reversal of the increased vascular permeability induced by the administration of plasminogen activators.

CONCLUSIONS

These data show that plasminogen activation causes an increase in vascular permeability that is inhibited by DDAVP; ASA blunts this action of t-PA and prevents the DDAVP blockade of the increase in permeability induced by t-PA in this rabbit model.

Localization and quantification of histamine in injured skin as parameters for the timing of wounds

Localization and estimation of the histamine (HA) content in skin wound edges in 86 Sprague-Dawley rats and three cases of human injuries were carried out by a microfluorimetric method specific for this amine which forms a complex with o-phthalaldehyde (OPT). Distribution and density of the mast cells in the same areas were observed at the same time by toluidine blue stain. In all skin specimens with antemortem wounds, both the epidermis and upper dermis exhibit extracellular yellowish fluorescence of the HA-OPT complex. The fluorescent zone spreads in the wound edges with the lapse of time in vital injuries. The HA content increases gradually up to 30 min and then the yellow histamine fluorescence in areas 0-200 microns from the wound edge decreases. None of these features can be observed in normal skin and postmortem-injured skin. Mast cell degranulation can be demonstrated in all antemortem-injured skin. No statistical relationship exists between the number of mast cells and the HA-OPT fluorescence in either ante- or postmortem-injured groups. This study indicates that skin HA microfluorimetry by the OPT method is of practical value for distinguishing ante- from the postmortem wounds and for timing antemortem wounds.

Plasma histamine in patients with chronic renal failure and nephrotic syndrome

Plasma histamine concentrations were measured using a commercially available monoclonal antibody radioimmunoassay in 38 patients with nephrotic syndrome, end stage renal failure, those receiving haemodialysis, and those receiving continuous ambulatory peritoneal dialysis to determine whether histamine may mediate damage to glomerular capillaries and arterial endothelium. Plasma histamine concentrations were significantly increased in all four patient groups when compared with those of controls and were the highest in two patients with pruritus. Raised plasma histamine concentrations in such patients are consistent with the hypothesis that histamine may contribute to the damage to glomerular capillaries and to arterial endothelium. These effects may be relevant to the pathogenesis of glomerular disease and atherosclerosis. Histamine may also contribute to the pathogenesis of pruritus in patients with chronic renal failure.

Cytokeratin filament modulation in pulmonary microvessel endothelial cells by vasoactive agents and culture confluency

Recently, bovine pulmonary microvascular endothelial cells (PMV) were shown to contain cytokeratin 8 and 19 intermediate filaments (Patton et al., 1990). In this study, we examine the effect of culture contiguity and vasoactive agents on the content and assembly of cytokeratins in PMV. Immunofluorescent staining of PMV cultures show a progressive increase in cytokeratin filament assembly. In freshly plated PMV, keratin appears as hazy staining (less than 4 hr) and later organizes into keratin 'plaques' (4 days) associated with cell-cell contacts; post confluent (greater than 7 days) PMV cultures contain fully assembled cytokeratin filaments which extend to the cell periphery and approach filaments in apposed cells. Vimentin filaments are also present in freshly plated PMV cultures but unlike cytokeratins, become less filamentous at confluency. This cell density-dependent modulation of cytokeratins is also demonstrated by densitometric analysis of autoradiographs of 35S-methionine labeled keratins in which PMV keratin content is elevated at high cell densities, while vimentin content remains constant. Desmoplakins I and II, components of desmosomes, could not be demonstrated in PMV by immunoblotting. PMV treated with permeability modulating agents (4 x 10(-3) M EGTA, 1 microM cytochalasin B, 1 microM bradykinin, 1 microM A23187, and 1 microM PMA) exhibit border retraction and altered keratin filament staining. From these studies we conclude: 1) cytokeratin 8 and 19 containing intermediate filaments are present in confluent PMV cultures with vimentin but without desmosomes, 2) the state of assembly of PMV cytokeratin and vimentin filaments appears to be oppositely affected by culture contiguity, and 3) treatment of monolayers with vasoactive agents alters the state of assembly of cytokeratin filaments. We speculate that modulation of cytokeratin assembly in PMV may be involved in regulation of pulmonary microvascular structure and function.

Histamine synthesis and catabolism in various tissues in diabetic rats

In view of the observations that (1) plasma histamine concentrations are significantly higher in diabetic patients and diabetic rats than those in controls, and (2) tissue concentrations of histamine are elevated in rats with experimental diabetes, we have investigated histamine synthesis, as reflected by histidine decarboxylase (HDC) activity, and histamine catabolism, as reflected by histaminase activity, in various tissues of the diabetic rat. Rats with streptozotocin-induced diabetes mellitus (DM) showed an increase in histamine synthesis in various tissues; this was most marked in the aorta and to a lesser, but significant, extent in the kidneys, lungs, and heart, but not in the brain, stomach, or skin. Tissue content of histamine was significantly increased in all tissues except the stomach and skin. We conclude that tissue histamine synthesis is significantly increased in diabetic animals and that this increase is most marked in the aorta. The elevation in HDC activity in these tissues probably accounts for the increase in tissue and plasma concentrations of histamine in diabetic animals, since there is no change in histamine catabolism. This increase in histamine synthesis and release may contribute to the pathogenesis of endothelial damage in diabetic microangiopathy and macroangiopathy.

Ultrastructural and three-dimensional analysis of the contractile cells of the cutaneous microvasculature

The three-dimensional relationships between smooth muscle cells and endothelial cells and between pericytes and endothelial cells in four segments of the microcirculation were analyzed by computer reconstructions from serial electron micrographs. In elastic-containing arterioles, the smooth muscle cells formed an inner longitudinal layer above and parallel to the elastica and an outer spiral layer. In the terminal arterioles the two layers of smooth muscle cells and elastica were replaced by a single smooth muscle cell that completely encircled the endothelial cell tube. The pericytes in the post-capillary venules completely encircled and gripped the endothelium through multiple contact points from their lateral processes. In the large venules the pericytes only partially encircled the endothelial cell tube and were more randomly placed.

Chloride efflux in cyclic AMP-induced configurational change of bovine pulmonary artery endothelial cells

Elevation of cellular cyclic AMP by agents such as isoproterenol plus 3-isobutyl-1-methylxanthine produced rapid and reversible dendritic formation of bovine pulmonary artery endothelial cells in the monolayer. The effect did not occur with exposure of the cells to a variety of other vasoactive agents, calcium ionophore, phorbol ester, or cyclic GMP. The cyclic AMP-induced configurational change was completely inhibited by 2.5 mM N-phenylanthranilic acid or 145 mM sodium gluconate (Cl- channel inhibitors) and was partially inhibited by 2.5 mM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), but it was not affected by deprivation of Ca2+ or Na+ ion, 1 mM bumetanide (Cl- cotransport inhibitor), 1 mM amiloride (Na+/H+ exchange inhibitor), 0.1 mM verapamil (Ca2+ channel inhibitor), or 5 mM BaCl2 (K+ channel inhibitor), by change in cellular pH, or by pertussis toxin. Trifluoperazine (calmodulin inhibitor, 50 microM), 1 mM EGTA plus 100 microM 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, intracellular Ca2+ antagonist), and 5 microM cytochalasin B also produced cellular retraction, but these changes were not blocked by chloride channel inhibition. In the presence of 0.1 mM ouabain plus 0.1 mM bumetanide, 36Cl- uptake was decreased by isoproterenol plus isobutylmethylxanthine while its efflux was enhanced. N-Phenylanthranilic acid inhibited the stimulated efflux. We conclude that cyclic AMP induces a configurational change of endothelial cells that is related to Cl- efflux from the cells; the cellular effects may play a role in vascular function.

Modulation of cultured pulmonary microvessel and arterial endothelial cell barrier structure and function by serotonin

Pulmonary microvessel endothelial cell and pulmonary artery endothelial cell monolayers in tissue culture were treated with serotonin (5-hydroxytryptamine; 5-HT) alone or in conjunction with histamine, bradykinin, the thromboxane analog U-46619, and the actin modulating agent cytochalasin B. After agent treatment, cross-sections through endothelial cell (EC) monolayers were examined by light microscopy and the percentage and widths of intercellular openings were quantitated. To correlate structural changes in the endothelial barrier with an alteration in permeability, EC monolayers cultured on micropore filters were assayed for transit of Evan's blue albumin (EBA) following treatment with vasoactive mediators. 5-HT was found to decrease the patency of endothelial junctions by up to 94%, compared to untreated monolayers, and to prevent or reverse the appearance of interendothelial gaps induced by histamine, bradykinin, U-46619, and cytochalasin B. The 5-HT effect was dose and time dependent, with a maximal increase in junctional apposition observed at a concentration of 10(-6) M for 30 min. This response was significantly blocked by the 5-HT antagonists LSD and ketanserin. The formation or reduction of interendothelial gaps by histamine, bradykinin, and U-46619 and by 5-HT, respectively, was positively correlated to changes in monolayer permeability to EBA. These results suggest that pulmonary edema caused by inflammatory mediators in part may be a consequence of transient increases in pulmonary EC junctional gaps, and that 5-HT may contribute to the homeostatic maintenance of endothelial barrier integrity.

Effect of phalloidin on structure and permeability of rete capillaries in the normal and hypoxic state

The effects of 10(-6) M phalloidin on reperfusion-injured blood capillary structure and permeability were studied in the countercurrent perfused rete mirabile of the eel swim bladder. In the normal rete, the addition of phalloidin to the perfusion medium did not induce morphological or functional changes. When flow was arrested for 30 minutes, during which time the capillaries were exposed to inhibitors of ATP generation, and flow was then resumed with an oxygenated medium, cell membrane blebs and vacuolization, mitochondrial swelling, pericyte shrinkage, and interstitial space edema were observed. The permeability coefficients for labeled albumin, sucrose, and sodium increased to three to four times baseline values, whereas the permeability to water was not significantly modified. When the same protocol was repeated with phalloidin present in the medium throughout the experiment, the structural integrity of the endothelial cells was completely preserved and pericyte shrinkage was abolished, but interstitial space edema still occurred. The permeability to albumin, sucrose, and sodium increased only to 1.5 times baseline values, a significantly decreased increment in comparison with the experiments performed without phalloidin. We concluded that although phalloidin does not improve the capillary barrier of the normal rete, it provides protection against the structural and functional damage induced by hypoxia and reperfusion.

The endothelial cell cytoskeleton modulates extravascular polymorphonuclear leukocyte accumulations in vivo

Actin microfilaments, key elements in the endothelial cell (EC) cytoskeleton, have been noted in in vitro studies to play a modulating role in the diapedesis of polymorphonuclear leukocytes (PMN). The role of the cytoskeleton in PMN diapedesis in vivo was the subject of this study. Small skin abrasions were produced in rabbits. Cytoskeletal manipulation was accomplished by local application of phalloidin which promotes microfilament assembly or cytochalasin B which causes their disassembly, prior to addition of a chemotaxin. When the initial treatment to the abrasion site was saline, the secondary addition of more saline resulted in PMN accumulations, expressed as PMN/mm3 of 36 +/- 19, while 10(-4) M cytochalasin B led to 91 +/- 32 (P less than 0.05). Secondary addition of chemotaxins or histamine also led to significant PMN accumulations of 169 +/- 54 with 10(-8) M leukotriene (LT) B4, 318 +/- 85 with zymosan-activated plasma (ZAP), and 158 +/- 48 with 10(-4) M histamine. When the initial treatment was 10(-8) M phalloidin, PMN accumulations were reduced to 31 +/- 22 with cytochalasin B (P less than 0.05 relative to saline as initial treatment); 63 +/- 43 with LTB4 (P less than 0.05); 137 +/- 48 with ZAP (P less than 0.05); and 51 +/- 35 with histamine (P less than 0.05). In contrast, initial blister treatment with cytochalasin B rather than saline increased PMN accumulations in response to LTB4, 291 +/- 71 (P less than 0.05), and histamine, 270 +/- 56 (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Atriopeptin inhibition of thrombin-mediated changes in the morphology and permeability of endothelial monolayers

To determine the role of endothelial atriopeptin (AP) receptors, we examined the effect of AP-III on the morphology and macromolecular permeability of monolayer cultures of bovine aortic endothelial cells. AP-III alone (10(-9)-10(-6) M) had no observable effect on the morphology of the monolayers or their permeability to 125I-labeled albumin. However, incubation of the endothelial monolayers with AP-III (10(-8)-10(-6) M) antagonized thrombin-induced (1 unit/ml) cell-shape change and the formation of intercellular gaps. AP-III also opposed the effect of thrombin on the distribution of actin filaments in the endothelial cytoskeleton. Further, thrombin caused a 2-fold increase in monolayer permeability to 125I-labeled albumin, which was abolished by 10(-8)-10(-6) M AP-III pretreatment. Taken together with the findings that AP-III exhibited specific and saturable binding in these cells, these data suggest that AP regulates endothelial permeability through a receptor-mediated process.

Vasoactive amines and eicosanoids interactively regulate both polymorphonuclear leukocyte diapedesis and albumin permeability in vitro

Previously we reported that cultured endothelial cells (ECs) can promote or inhibit polymorphonuclear leukocyte (PMN) diapedesis and albumin permeability in vitro by altering monolayer intercellular integrity (an activity influenced by pretreatment with exogenous amines). Endothelial eicosanoid release was also seen to stimulate both PMN motility and diapedesis. We now demonstrate that these endothelial activities are related. Thromboxane (Tx) B2 pretreatment of ECs results in increased diapedesis and permeability across the monolayers whereas 6-keto-PGF1 alpha pretreatment has the opposite effects, demonstrating that these eicosanoids exert direct effects upon ECs, in addition to their direct effects upon PMNs as previously described. Norepinephrine (NE) or serotonin (5HT) pretreatment of ECs inhibits the release of TxB2 and 6-keto-PGF1 alpha, with the result that the stimulation of PMN motility by these EC metabolites is eliminated. In contrast, histamine increases the endothelial release of eicosanoids, resulting in a further increase in PMN motility. We conclude that histamine directly reduces EC monolayer integrity (by altering the endothelial cytoskeleton) and also increases eicosanoid release, actions which both enhance PMN motility and further reduce monolayer integrity. Conversely, NE and 5HT both increase intercellular integrity and decrease eicosanoid release, thereby decreasing PMN motility, diapedesis, and albumin permeability.

The rapid induction by interleukin-2 of pulmonary microvascular permeability

The clinical use of interleukin-2 (IL-2) is limited by severe cardiopulmonary dysfunction. This study examines the mechanism of respiratory failure related to IL-2, using sheep with chronic lung lymph fistulae. Awake animals were infused with an intravenous (I.V.) bolus of IL-2 10(5) U/kg (n = 5) or its excipient (EXC) control (n = 3), every 8 hours for 4 to 5 days. Cardiopulmonary function was monitored daily for at least one 8-hour period. Within 2 hours after each IL-2 administration, mean pulmonary arterial pressure (MPAP) rose. On Day 1, the mean rise was from 13 to 26 mmHg (p less than 0.05), and on Day 5, to 29 mmHg (p less than 0.05). MPAP returned to baseline levels after 2-3 hours. Pulmonary arterial wedge pressure was unchanged from 4 mmHg. There were transient falls in arterial oxygen tension, from 88 to 77 mmHg on Day 1 and to 73 mmHg (p less than 0.05) on Day 5. Lung lymph flow (QL) rose from 2.4 to 6.8 ml/30 minutes (p less than 0.05) on Day 1, and from 4.7 to 10.2 ml/30 minutes (p less than 0.05) on Day 5, whereas the lymph/plasma protein ratio increased on Day 1 from 0.69 to 0.83 (p less than 0.05) and from 0.63 to 0.71 (p less than 0.05) on Day 5. This documents an increase in pulmonary microvascular permeability. Thromboxane (Tx)B2 levels increased transiently after each IL-2 injection in plasma from 195 to 340 pg/ml (p less than 0.05) and in lung lymph from 222 to 772 pg/ml (p less than 0.05) on Day 1, and to similar levels on Day 5. There was a progressive rise in cardiac output from 5.7 to 8.6 1/minute (p less than 0.05) during the 5 days of infusion. Systemic blood pressure did not change. Temperature rose from 39.1 to 41.2 C (p less than 0.05), and shaking chills were common. There was a progressive fall in leukocyte count, from 8.4 to 3.2 X 10(3)/mm3 (p less than 0.05) by Day 5, reflecting a 77% fall in lymphocytes. Lung lymph lymphocyte counts rose, and lymphocyte clearance increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial cell junctional integrity modulation by serotonin: an ultrastructural analysis

We have reported previously that exogenous serotonin (5-hydroxytryptamine, 5-HT) alters cultured bovine aortic endothelial cell (BAEC) structural integrity by modulating the assembly of stress fibers. In the present study a 5-HT stimulus-coupled change in BAEC junctional integrity was quantitated by determining the width and percentage of intercellular openings in a monolayer. BAEC treated with 5-HT at concentrations of 10(-9) M to 10(-3) M caused a significant dose-dependent decrease in interendothelial cell junctional openings compared to controls, with the greatest reduction induced at 10(-6) M (92% from control). Treatment of BAEC with histamine (10(-4) M) increased the junctional openings by 82% when compared to controls. This change could be prevented by either pretreatment of the monolayers with 5-HT or by adding 5-HT in conjunction with the histamine. To assess a direct interaction of 5-HT with actin filaments, cultured BAEC monolayers were extracted, treated with 5-HT, and processed for immunocytochemical localization of 5-HT using the Avidin-Biotin method. Electron microscopy revealed 5-HT antibody bound to actin filaments and dense in areas of filament intersection, which implies a role for internalized 5-HT in stimulating the assembly of an actin filament network. Collectively, these results suggest that 5-HT helps to regulate the endothelial junctional barrier by promoting actin filament formation and stability, which may in turn increase the junctional apposition between endothelial cells.

Serotonin uptake and configurational change of bovine pulmonary artery smooth muscle cells in culture

Although it is well known that endothelial cells transport serotonin (5-HT) from extracellular to intracellular locations, it has been generally assumed that smooth muscle cells do not accumulate 5-HT but, rather, respond to 5-HT through a receptor activity unrelated to uptake of this amine or via stimulation of endothelial-derived relaxing factor. In the present study smooth muscle cells (PASMC), isolated and cultured from bovine pulmonary artery, were evaluated for 5-HT uptake under a variety of conditions. 5-HT uptake was linear up to 15 min and the rate was seven- to eightfold higher than that by bovine pulmonary artery endothelial cells. There was intracellular metabolism of 5-HT to 5-hydroxyindoleacetic acid (5-HIAA). The uptake was inhibited by exposure to 4 degrees C, absence of Na+ from the medium, and agents such as imipramine, verapamil, ketanserin, and methiothepin. Like that of endothelial cells, 5-HT uptake by PASMC was stimulated by exposure of cells to anoxia for 24 hr. Unlike endothelial cells that showed no morphological changes, PASMC at early passage showed dendritic formation after 30-60 min exposure to 5-HT at a concentration as low as 10(-8) M. Although this configurational change in response to 5-HT was lost with passage of cells, transport of 5-HT by these cells was retained. The configurational change was blocked by agents that inhibited 5-HT uptake, such as imipramine, verapamil, ketanserin, and methiothepin; it was unaffected by inhibitors of protein kinase C, phospholipase C, and calmodulin or absence of Ca2+ from the medium. We conclude that PASMC, as well as endothelial cells, accumulate 5-HT; there appears to be a close relationship between 5-HT uptake and configurational change of early passaged PASMC in culture. The factor(s) required for the configurational change are absent in endothelial cells and lost during passage of PASMC.

Norepinephrine down-regulates the activity of protein S on endothelial cells

The adrenergic agonist norepinephrine is shown to stimulate endothelium to induce protein S release and degradation, leading to diminished anti-coagulant activity and to down-regulation of protein S cell surface-binding sites. Norepinephrine-induced release of intracellular protein S was blocked by the alpha 1-adrenergic antagonist prazosin (10(-7) M) but not by the alpha-adrenergic antagonist propranolol (10(-6) M) or the alpha 2-adrenergic antagonist yohimbine (10(-5) M) indicating that this response resulted from the specific interaction of norepinephrine with a class of alpha 1-adrenergic receptors not previously observed on endothelium. Attenuation of norepinephrine-induced release of protein S by pertussis toxin in association with the ADP-ribosylation of a 41,000-D membrane protein indicates that this intracellular transduction pathway involves a regulatory G protein. The observation that protein S was released from endothelium in response to maneuvers which elevate intracellular calcium or activate protein kinase C suggests that the response may be mediated via intermediates generated through the hydrolysis of phosphoinositides. Morphologic studies were consistent with a mechanism in which norepinephrine causes exocytosis of vesicles containing protein S. In addition to release of protein S, norepinephrine also induced loss of endothelial cell protein S-binding sites, thereby blocking effective activated protein C-protein S-mediated factor Va inactivation on the cell surface. Norepinephrine-mediated endothelial cell stimulation thus results in loss of intracellular protein S and suppression of cell surface-binding sites, modulating the anti-coagulant protein C pathway on the vessel wall. These studies define a new relationship between an anti-coagulant mechanism and the autonomic nervous system, and indicate a potential role for an heretofore unrecognized class of alpha 1-adrenergic receptors in the regulation of endothelial cell physiology.

Phalloidin enhances endothelial barrier function and reduces inflammatory permeability in vitro

Phalloidin, a potent microfilament toxin, induces polymerization of actin in vitro and in vivo. In a permeability assay, bovine aortic endothelial cell cultured on microcarrier beads exclude significantly more serum albumin after 30 min treatment with 10(-6), 10(-8), and 10(-10) M phalloidin than controls. Furthermore, pretreatment of microcarriers with 10(-8) M phalloidin significantly reduces permeability increases by histamine, bradykinin, thromboxane A2 mimetic, and cytochalasin B, (all at 10(-6) M). Phalloidin also causes significant surface area and perimeter increases in cultured endothelial cells. The cells also display increased acting stress fibers and show a weblike cytoskeletal pattern of microfilaments. These data suggest that in vitro the endothelial junctional barrier may be enhanced in part by assembly of actin filaments.

In situ localization of F-actin microfilaments in the vasculature of the porcine retina

The organization of F-actin microfilaments in the vascular endothelium of the porcine retina was studied in situ using rhodamine phalloidin labelling and fluorescence microscopy. A comparison was made between arterial and venous endothelial-cell microfilament distribution. The arterial cells in straight segments, bifurcations and branch points were elongated with their long axis in the direction of flow. Venous endothelial cells, on the other hand, were ellipsoid to rhomboid in shape throughout. F-actin was localized at the periphery of both arterial and venous endothelial cells. Prominent central microfilament bundles, similar to in vitro stress fibres, were oriented parallel to the long axis of arterial cells but were rarely present in venous cells. Only occasional venous endothelial cells contained short central actin filaments which were mainly in the venules. Central microfilaments were not identified in pre-capillary, capillary, or post-capillary endothelial cells. Incubation of the retinal organ cultures for 24 hr resulted in loss of the central microfilaments while peripheral staining persisted. Short-term incubation of the retinas in organ culture with low-dose cytochalasin B resulted in disruption of the central microfilaments while the peripheral actin microfilaments remained intact. The central microfilament bundles may reflect an adaptive response to arterial blood flow and may indeed be a sensitive dynamic system reflecting the influence of environmental factors on endothelial cells.

[50 years of phalloidine: its discovery, characterization and current and future applications in cell research]

Phalloidin, like the later-detected phallotoxins, consists of a cyclic heptapeptide backbone, the ring being crosslinked by a 2'-indolylthioether moiety (tryptathionine). After intraperitoneal administration--not per os--it will, after a short time, damage the liver specifically, presumably in consequence of its very tight binding to F-actin preventing its dissociation. This affinity can be utilized for a sensitive visual identification of F-actin by using fluorescent derivatives.

Cultured bovine aortic endothelial cells show increased histamine metabolism when exposed to oscillatory shear stress

Oscillatory shear stress applied to the lining of blood vessels causes endothelial cell injury, one of the essential postulated prerequisites to the development of atherosclerosis. The purpose of this investigation was to study effects of shear stress on bovine aortic endothelial cells (BAEC), in vitro, for varying lengths of time (6 h, 12 h, 24 h) on BAEC histamine content (HC) and histidine decarboxylase activity (HD). Low intensity stress (1.6 dynes/cm2) as well as intermediate and high intensity shear stresses (3.5 dynes/cm2 and 7.6 dynes/cm2) resulted in an accelerated HD (281%) and elevated HC (144%). These data indicate that oscillatory shear stress produces increases in histamine metabolism.

Serotonin induced actin polymerization and association with cytoskeletal elements in cultured bovine aortic endothelium

Serotonin, (5-hydroxytryptamine, 5-HT) binds to cultured endothelial cell stress fibers as identified by fluorescence microscopy and in vitro induces actin polymerization as measured by DNase 1 inhibition and differential centrifugation; the structural change in actin in the presence of 5-HT resembles actin paracrystals as visualized by negative staining under electron microscopy. These observations indicate that 5-HT, which is taken up by endothelium by a non-mediated diffusion, may interact directly with actin to affect cytoskeletal changes.

Changes in cytosolic Ca2+ associated with von Willebrand factor release in human endothelial cells exposed to histamine. Study of microcarrier cell monolayers using the fluorescent probe indo-1

A method for measuring fluorescence in anchored monolayers of human endothelial cells is described and used to demonstrate changes in the cytosolic free-calcium concentration ([Ca2+]c) in these cells exposed to histamine and thrombin; some endothelial responses to both agonists (e.g., mitogenesis) have been suggested to be Ca2+-mediated. Umbilical vein endothelial cells were cultured on microcarriers and loaded with the Ca2+ indicator, indo-1. Enzymatic cell detachment was avoided by monitoring the indo-1 fluorescence ratio (400/480 nm) of a stirred suspension of cell-covered microcarriers. Basal [Ca2+]c was estimated to be 70-80 nM. Thrombin induced a transient dose-dependent increase in [Ca2+]c, which was active-site dependent. Histamine stimulated a dose-dependent increase in [Ca2+]c, which was reversed by removal of histamine and inhibited competitively by the H1-receptor antagonist pyrilamine, but not by the H2-receptor antagonist cimetidine. Furthermore, histamine induced a dose-dependent secretion of von Willebrand factor, which paralleled the rise in [Ca2+]c and was similarly blocked by the H1-receptor antagonist, and which may contribute to platelet deposition at sites of inflammation.

Effects of forskolin on growth and morphology of cultured glial and cerebrovascular endothelial and smooth muscle cells

The present experiments were designed to evaluate the effectiveness of forskolin on cAMP production, growth and morphology on cell cultures of glia, endothelium and smooth muscle derived from brain microvessels. Forskolin significantly increased formation of cAMP and decreased incorporation of thymidine in all three cell types. The thymidine incorporation was reduced dose-dependently with maximal growth inhibition at 100 microM forskolin. A 1 hr preincubation with forskolin abolished thymidine incorporation by cells grown in fetal calf serum (FCS)-containing media over the following 24 hr. In cerebromicrovascular endothelium and smooth muscle, forskolin caused drastic and immediate changes of cell morphology and F-actin composition that were reversible. In glial cells, morphological changes were visible only after exposure to forskolin for more than 24 hr. These changes were accompanied by increased staining with antibodies against glial fibrillary acidic protein (GFAP). These findings support the contention of cAMP involvement in growth regulation of these cells and indicate that forskolin might be used as a tool to induce growth arrest and possible differentiation in cell cultures from mammalian brain.

Morphological alterations in endothelial cells from human aorta and umbilical vein induced by forskolin and phorbol 12-myristate 13-acetate: a synergistic action of adenylate cyclase and protein kinase C activators

The morphological effects on human endothelial cells of phorbol 12-myristate 13-acetate (PMA) and of agents that increase intracellular cAMP concentration were studied. The adenylate cyclase activator forskolin (10 microM), the cyclic nucleotide phosphodiesterase inhibitor methylisobutylxanthine (100 microM), dibutyryl-cAMP (10 microM), histamine (10 microM), and PMA (0.1 microM) significantly altered the morphology of human aortic and umbilical vein endothelial cells in primary cultures. These effects reached a maximum 40-80 min after the effector addition and became negligible 30-60 min after its removal. PMA and forskolin were strongly synergistic in altering endothelial cell morphology. All the effects of cAMP-elevating compounds and of PMA were abolished completely by 1 microM colchicine. In explants taken from human adult or child aortas, forskolin and PMA produced alterations in endothelial morphology qualitatively identical to those observed in endothelial cell cultures. Endothelium in these preparations closely resembled that found in zones of expected altered hemodynamic stresses of human aorta. Our data suggest that the morphology of endothelium in vivo may be regulated by separate or synergistic action of hormone-dependent adenylate cyclase and of inositol phospholipid turnover systems and might be important for maintenance of endothelial monolayer integrity under normal physiological and pathological conditions.

Protein phosphorylation in cultured endothelial cells

We have investigated the protein phosphorylation systems present in cultured bovine aortic and pulmonary artery endothelial cells. The cells contain cyclic AMP-dependent protein kinase, three calcium/calmodulin-dependent protein kinases, protein kinase C, and at least one tyrosine kinase. No cyclic GMP-dependent protein kinase activity was found. The cells also contained numerous substrates for cyclic AMP-dependent protein kinase and protein kinase C. Fewer substrates were found for the calcium/calmodulin-dependent protein kinases. There was little difference between either protein kinase activities or substrates when pulmonary artery endothelium was compared to aortic endothelium grown under similar culture conditions. It is likely that these various protein kinases and their respective substrate proteins are involved in mediating several of the actions of the hormones and drugs which affect the vascular endothelium.

Density-dependent contraction of the endothelial nascent histamine pool by exogenous heparin

The aortic endothelial cell nascent histamine pool has been implicated in the control of vessel wall permeability under conditions of stress and injury. We report the contraction of this histamine pool in low density bovine aortic endothelial cell (BAEC) cultures by exogenous heparin. Untreated BAEC exhibit a decline in histamine content in 3-day cultures with increasing plating density between 1000 and 16,000 cells/cm2. Heparin abolished this density-related difference by effecting a 67% contraction of the histamine pool in the lowest density cultures. This effect was reversible and specific to heparin. At a confluent density, endothelial cells secrete heparin-like glycosaminoglycans which affect smooth muscle and endothelial metabolism. We propose that the metabolic effects of exogenous heparin, and perhaps endogenous heparins, extend to specific modulations of the BAEC nascent histamine pool.

Serotonin, norepinephrine, and histamine mediation of endothelial cell barrier function in vitro

The effects of serotonin (5-hydroxytryptamine, 5-HT), norepinephrine (NE), and histamine on endothelial cell barrier function were examined in vitro. Bovine aortic endothelial (BAE) cells grown to confluence on microcarriers formed a measurable barrier to the passage of a trypan blue dye-bovine serum albumin conjugate (TB-BSA) from the culture medium into the microcarrier matrix. Vascular smooth muscle (VSM) cells or Swiss 3T3 fibroblasts impeded TB-BSA diffusion only 42% and 56%, respectively, relative to BAE cells. These results suggest that barrier formation may be an endothelial cell-specific phenomenon. Treatment of BAE cells with histamine was associated with 2- to 3-fold increases in the rate of TB-BSA diffusion. In contrast, treatment with 5-HT or NE at concentrations ranging from normal to pathophysiological circulating plasma levels significantly impeded TB-BSA diffusion by up to 43% and 33%, respectively, relative to untreated controls. The barrier-modulating effects of the vasoactive amines were dose-dependent, cell-specific, and in some cases appear to be receptor-mediated. These results are consistent with previous reports that histamine increases vascular permeability in part by affecting diffusion between endothelial cells; they support the hypothesis that 5-HT and NE contribute to the maintenance of the endothelial barrier in vivo.

Eicosanoid modulation of stress fibers in cultured bovine aortic endothelial cells

Leukotrienes (LT) B4, LTD4, and thromboxanes (TX) are cytotoxic, and increase microvascular permeability. Because endothelial stress fibers are theorized to be part of the cytoskeletal mechanism by which microvessels maintain their barrier function, the effect of these eicosanoids on stress fibers in bovine aortic endothelial cells was tested. LTB4, LTD4, and TXB2 each decreased stress fiber numbers by 93%, 62%, and 66%, respectively, when compared to controls (P less than 0.01). In contrast, endothelial cells treated with prostacyclin (PGI2) at 10(-7) M, produced a significant increase (P greater than 0.01) in stress fiber numbers, 211% to that of controls. Azaprostanoic acid (13-APA) and FPL55712, receptor antagonists to TX and slow-reacting substance of anaphylaxis (SRS) receptors, respectively, the cyclooxygenase inhibitor ibuprofen, and the TX synthase inhibitors imidazole and ketoconazole were used to test for possible endothelial cell receptor mediation and de novo prostanoid synthesis associated with inflammatory eicosanoid-induced disassembly of stress fibers. Each pharmacologic agent inhibited the LTD4- and TXB2-induced decreases in stress fibers; LTB4-stimulated stress fiber decreases were inhibited only by pretreatment with TX synthase blockers. These data suggest that increased permeability associated with inflammatory eicosanoid metabolites may have as a common target stress fiber disassembly, and the mechanism may be receptor-mediated. That cyclooxygenase and TX synthase blockers inhibited the eicosanoid action suggests that endogenous TX synthesis may be a step in the mechanism. PGI2 enhancement of the microvascular barrier may be related to the effect of PGI2 on promoting stress fiber assembly. In summary, endothelial cell synthesized autocoids derived from arachidonic acid may help to regulate microvascular permeability by way of their action on stress fiber assembly/disassembly, and unbalanced prostanoid secretion by way of LT stimulation may result in a loss of the microvascular barrier and increased permeability.