Human saphenous vein endothelial cells express a tetrodotoxin-resistant, voltage-gated sodium current

The effects of Tityus bahiensis scorpion venom on the contractility of jejunum, vas deferens, and the aorta is differentially affected by tetrodotoxin

The pharmacological effects of the crude venom of the scorpion Tityus serrulatus or its isolated toxins have been widely studied. However, few studies are available on Tityus bahiensis venom. We recently discovered that T. serrulaus venom leads to the release of tetrodotoxin-resistant acetylcholine. Thus, our objective was to verify whether T. bahiensis venom could have a similar action in the jejunum. Furthermore, we evaluated the possibility that this action occur in other tissues innervated by the autonomic nervous system. Thus, organ bath studies were conducted to evaluate the contractile and relaxant effects of venom on the jejunum, vas deferens and aorta of rats in the presence or absence of tetrodotoxin. We observed that jejunum, vas deferens and aorta contracted when the T. bahiensis venom was applied. In the jejunum, the venom reveals a contractile component resistant to tetrodotoxin. It also was able to relax pre-contracted preparations of jejunum and aorta but not vas deferens. Only in the aorta, the relaxation was resistant to tetrodotoxin. The effects of scorpion venoms are attributed to its action on ionic channels leading to neuronal depolarization and neurotransmitter release. Our results indicated that a similar mechanism is present in the observed effects of the venom. However, another mechanism must be present in the venom-induced contraction in the jejunum and relaxation in the aorta. Possible involvement of tetrodotoxin-resistant sodium channels or non-neuronal release of neurotransmitters is discussed. We emphasize that the study of the Tityus scorpion's venom, especially T. bahiensis, is of great importance because it can unveil unknown pharmacological and physiological mechanisms of excitable cells.

Critical contribution of Na+-Ca2+ exchanger to the Ca2+-mediated vasodilation activated in endothelial cells of resistance arteries

Na⁺-Ca²⁺ exchanger (NCX) contributes to control the intracellular free Ca²⁺ concentration ([Ca²⁺]_i), but the functional activation of NCX reverse mode (NCXrm) in endothelial cells is controversial. We evaluated the participation of NCXrm-mediated Ca²⁺ uptake in the endothelium-dependent vasodilation of rat isolated mesenteric arterial beds. In phenylephrine-contracted mesenteries, the acetylcholine (ACh)-induced vasodilation was abolished by treatment with the NCXrm blockers SEA0400, KB-R7943, or SN-6. Consistent with that, the ACh-induced hyperpolarization observed in primary cultures of mesenteric endothelial cells and in smooth muscle of isolated mesenteric resistance arteries was attenuated by KB-R7943 and SEA0400, respectively. In addition, both blockers abolished the NO production activated by ACh in intact mesenteric arteries. In contrast, the inhibition of NCXrm did not affect the vasodilator responses induced by the Ca²⁺ ionophore, ionomycin, and the NO donor, S-nitroso- N-acetylpenicillamine. Furthermore, SEA0400, KB-R7943, and a small interference RNA directed against NCX1 blunted the increase in [Ca²⁺]_i induced by ACh or ATP in cultured endothelial cells. The analysis by proximity ligation assay showed that the NO-synthesizing enzyme, eNOS, and NCX1 were associated in endothelial cell caveolae of intact mesenteric resistance arteries. These results indicate that the activation of NCXrm has a central role in Ca²⁺-mediated vasodilation initiated by ACh in endothelial cells of resistance arteries.-Lillo, M. A., Gaete, P. S., Puebla, M., Ardiles, N. M., Poblete, I., Becerra, A., Simon, F., Figueroa, X. F. Critical contribution of Na⁺-Ca²⁺ exchanger to the Ca²⁺-mediated vasodilation activated in endothelial cells of resistance arteries.

The influence of sodium on pathophysiology of multiple sclerosis

Multiple sclerosis (MS) is a chronic, inflammatory, autoimmune disease of the central nervous system, and is an important cause of disability in young adults. In genetically susceptible individuals, several environmental factors may play a partial role in the pathogenesis of MS. Some studies suggests that high-salt diet (>5 g/day) may contribute to the MS and other autoimmune disease development through the induction of pathogenic Th17 cells and pro-inflammatory cytokines in both humans and mice. However, the precise mechanisms of pro-inflammatory effect of sodium chloride intake are not yet explained. The purpose of this review was to discuss the present state of knowledge on the potential role of environmental and dietary factors, particularly sodium chloride on the development and course of MS.

The cardiac sodium current Na(v)1.5 is functionally expressed in rabbit bronchial smooth muscle cells

A collagenase-proteinase mixture was used to isolate airway smooth muscle cells (ASMC) from rabbit bronchi, and membrane currents were recorded using the whole cell patch-clamp technique. Stepping from -100 mV to a test potential of -40 mV evoked a fast voltage-dependent Na(+) current, sometimes with an amplitude of several nanoamperes. The current disappeared within 15 min of exposure to papain + DTT (n = 6). Comparison of the current in ASMC with current mediated by NaV1.5 α-subunits expressed in human embryonic kidney cells revealed similar voltage dependences of activation (V1/2 = -42 mV for NaV1.5) and sensitivities to TTX (IC50 = 1.1 and 1.2 μM for ASMC and NaV1.5, respectively). The current in ASMC was also blocked by lidocaine (IC50 = 160 μM). Although veratridine, an agonist of voltage-gated Na(+) channels, reduced the peak current by 33%, it slowed inactivation, resulting in a fourfold increase in sustained current (measured at 25 ms after onset). In current-clamp mode, veratridine prolonged evoked action potentials from 37 ± 9 to 1,053 ± 410 ms (n = 8). Primers for NaV1.2-1.9 were used to amplify mRNA from groups of ∼20 isolated ASMC and from whole bronchial tissue by RT-PCR. Transcripts for NaV1.2, NaV1.3, and NaV1.5-1.9 were detected in whole tissue, but only NaV1.2 and NaV1.5 were detected in single cells. We conclude that freshly dispersed rabbit ASMC express a fast voltage-gated Na(+) current that is mediated mainly by the NaV1.5 subtype.

Sodium channels and microglial function

Microglia are resident immune cells that provide continuous surveillance within the central nervous system (CNS) and respond to perturbations of brain and spinal cord parenchyma with an array of effector functions, including proliferation, migration, phagocytosis, secretions of multiple cytokines/chemokines and promotion of repair. To sense alterations within their environment, microglia express a large number of cell surface receptors, ion channels and adhesion molecules, which activate complex and dynamic signaling pathways. In the present chapter, we review studies that demonstrate that microglia in vivo and in vitro express specific voltage-gated sodium channel isoforms, and that blockade of sodium channel activity can attenuate several effector functions of microglia. These studies also provide strong evidence that Nav1.6 is the predominant sodium channel isoform expressed in microglia and that its activity contributes to the response of microglia to multiple activating signals.

Angiogenic functions of voltage-gated Na+ Channels in human endothelial cells: modulation of vascular endothelial growth factor (VEGF) signaling

Voltage-gated sodium channel (VGSC) activity has previously been reported in endothelial cells (ECs). However, the exact isoforms of VGSCs present, their mode(s) of action, and potential role(s) in angiogenesis have not been investigated. The main aims of this study were to determine the role of VGSC activity in angiogenic functions and to elucidate the potentially associated signaling mechanisms using human umbilical vein endothelial cells (HUVECs) as a model system. Real-time PCR showed that the primary functional VGSC α- and β-subunit isoforms in HUVECs were Nav1.5, Nav1.7, VGSCβ1, and VGSCβ3. Western blots verified that VGSCα proteins were expressed in HUVECs, and immunohistochemistry revealed VGSCα expression in mouse aortic ECs in vivo. Electrophysiological recordings showed that the channels were functional and suppressed by tetrodotoxin (TTX). VGSC activity modulated the following angiogenic properties of HUVECs: VEGF-induced proliferation or chemotaxis, tubular differentiation, and substrate adhesion. Interestingly, different aspects of angiogenesis were controlled by the different VGSC isoforms based on TTX sensitivity and effects of siRNA-mediated gene silencing. Additionally, we show for the first time that TTX-resistant (TTX-R) VGSCs (Nav1.5) potentiate VEGF-induced ERK1/2 activation through the PKCα-B-RAF signaling axis. We postulate that this potentiation occurs through modulation of VEGF-induced HUVEC depolarization and [Ca(2+)](i). We conclude that VGSCs regulate multiple angiogenic functions and VEGF signaling in HUVECs. Our results imply that targeting VGSC expression/activity could be a novel strategy for controlling angiogenesis.

Resveratrol protects human endothelium from H(2)O(2)-induced oxidative stress and senescence via SirT1 activation

AIM

Silencing information regulator (SirT1), a NAD-dependent histone deacetylase, is an essential mediator of longevity in normal cells by calorie restriction. SirT1 has many biological functions, including transcription regulation, cell differentiation inhibition, cell cycle regulation, and anti-apoptosis. Resveratrol (RV)-induced SirT1 activation also improves endothelial dysfunction and suppresses vascular inflammation. In this study, we investigated the roles of RV-induced SirT1 activation in endothelial cells under oxidative stress.

METHODS

SirT1 mRNA expression levels were examined in the endothelium layer (endothelial cells) of cardiac coronary vessels from patients receiving coronary artery bypass graft surgery (CABG) surgery and aged rats using reverse transcriptase polymerase chain reaction (RT-PCR). To further explore the effect of SirT1 activation on oxidative stress-induced aging, senescence-associated β-galactosidase (SA-β-gal) expression in RV-treated human umbilical vein endothelial cells (HUVECs) with or without H(2)O(2) treatment was evaluated.

RESULTS

SirT1 expression was decreased in aged and atherosclerotic vessels in vivo, and significantly reduced in endothelial cells purified from vessel tissues. Furthermore, SirT1 levels were dose-dependently increased in RV-treated HUVECs. The SA-β gal assay showed that RV inhibited the senescent phenotype of H(2)O(2)-treated HUVECs. Reactive oxygen species (ROS) production and the percentage of cells positive for SA-β gal were significantly increased in siRNA-SirT1 (knockdown of SirT1 expression)-treated HUVEC cells. Importantly, the treatment effect of RV was significantly abolished in the oxidative effects of H(2)O(2)-treated HUVECs by siRNA-SirT1.

CONCLUSION

Our data suggested that SirT1 could be a crucial factor involved in the endothelial cells of atherosclerotic CAGB patients and aging rats. RV is a potential candidate for preventing oxidative stress-induced aging in endothelial cells. RV may also prevent ROS-induced damage via increased endothelial SirT1 expression.

Voltage-gated Na+ channels: potential for beta subunits as therapeutic targets

BACKGROUND

Voltage gated Na(+) channels (VGSCs) contain a pore-forming alpha subunit and one or more beta subunits. VGSCs are involved in a wide variety of pathophysiologies, including epilepsy, cardiac arrhythmia, multiple sclerosis, periodic paralysis, migraine, neuropathic and inflammatory pain, Huntington's disease and cancer. Increasing evidence implicates the beta subunits as key players in these disorders.

OBJECTIVE

To review the recent literature describing the multifunctional roles of VGSC beta subunits in the context of their role(s) in disease.

METHODS

An extensive review of the literature on beta subunits.

RESULTS/CONCLUSION

beta subunits are multifunctional. As components of VGSC complexes, beta subunits mediate signaling processes regulating electrical excitability, adhesion, migration, pathfinding and transcription. beta subunits may prove useful in disease diagnosis and therapy.

An emerging role for voltage-gated Na+ channels in cellular migration: regulation of central nervous system development and potentiation of invasive cancers

Voltage-gated Na(+) channels (VGSCs) exist as macromolecular complexes containing a pore-forming alpha subunit and one or more beta subunits. The VGSC alpha subunit gene family consists of 10 members, which have distinct tissue-specific and developmental expression profiles. So far, four beta subunits (beta1-beta4) and one splice variant of beta1 (beta1A, also called beta1B) have been identified. VGSC beta subunits are multifunctional, serving as modulators of channel activity, regulators of channel cell surface expression, and as members of the immunoglobulin superfamily, cell adhesion molecules (CAMs). beta subunits are substrates of beta-amyloid precursor protein-cleaving enzyme (BACE1) and gamma-secretase, yielding intracellular domains (ICDs) that may further modulate cellular activity via transcription. Recent evidence shows that beta1 regulates migration and pathfinding in the developing postnatal CNS in vivo. The alpha and beta subunits, together with other components of the VGSC signaling complex, may have dynamic interactive roles depending on cell/tissue type, developmental stage, and pathophysiology. In addition to excitable cells like nerve and muscle, VGSC alpha and beta subunits are functionally expressed in cells that are traditionally considered nonexcitable, including glia, vascular endothelial cells, and cancer cells. In particular, the alpha subunits are up-regulated in line with metastatic potential and are proposed to enhance cellular migration and invasion. In contrast to the alpha subunits, beta1 is more highly expressed in weakly metastatic cancer cells, and evidence suggests that its expression enhances cellular adhesion. Thus, novel roles are emerging for VGSC alpha and beta subunits in regulating migration during normal postnatal development of the CNS as well as during cancer metastasis.

Phenytoin protects central axons in experimental autoimmune encephalomyelitis

Axon degeneration is a major contributor to non-remitting deficits in multiple sclerosis (MS). Thus the development of therapies to provide protection of axons has elicited considerable interest. Voltage-gated sodium channels have been implicated in the injury cascade leading to axonal damage, and sodium-channel blockers have shown efficacy in ameliorating axonal damage in disease models following anoxia, trauma and damaging levels of nitric oxide (NO). Here we discuss studies in our laboratory that examined the protective effects of phenytoin, a well-characterized sodium-channel blocker, in the inflammatory/demyelinating disorder experimental autoimmune encephalomyelitis (EAE), a model of MS. Administration of phenytoin to C57/Bl6 mice inoculated with rat myelin oligodendrocyte glycoprotein (MOG) provides improved clinical status, preservation of axons, enhanced action potential conduction and reduced immune infiltrates compared to untreated mice with EAE. Moreover, continuous treatment with phenytoin provides these protective actions for at least 180 days post-MOG injection. The withdrawal of phenytoin from mice inoculated with MOG, however, is accompanied by acute exacerbation of EAE, with significant mortality and infiltration of immune cells in the CNS. Our studies demonstrate the efficacy of phenytoin as a neuroprotectant in EAE. Our results also, however, indicate that we need to learn more about the long-term effects of sodium-channel blockers, and of their withdrawal, in neuroinflammatory disorders.

Exacerbation of experimental autoimmune encephalomyelitis after withdrawal of phenytoin and carbamazepine

OBJECTIVE

In vitro observations and studies in murine experimental autoimmune encephalomyelitis (EAE) have shown protective effects of sodium channel blockers on central nervous system axons and improved clinical status when treatment is continued throughout the period of observation. Several clinical studies of sodium channel blockers are under way in patients with multiple sclerosis. Here we asked whether a protective effect would persist after withdrawal of a sodium channel blocker.

METHODS

We studied a mouse model of myelin oligodendrocyte glycoprotein-induced EAE treated with phenytoin or carbamazepine.

RESULTS

Both phenytoin and carbamazepine significantly improved the clinical course of the disease. Withdrawal of phenytoin resulted in acute exacerbation, accompanied by a significantly increased inflammatory infiltrate within the central nervous system and the death of nearly 60% of EAE mice. There were no clinical worsening or deaths in control mice after withdrawal of phenytoin. Withdrawal of carbamazepine led to acute worsening of EAE symptoms, increased inflammatory infiltrate, and was associated with the death of 8% of mice.

INTERPRETATION

These results, together with results showing effects of sodium channel blockers in immune cells, raise questions about the long-term effects of sodium channel blockers in neuroinflammatory disorders, and suggest that clinical studies of sodium channel blockers in these disorders should be planned carefully.

β-Subunits of voltage-gated sodium channels in human prostate cancer: quantitative in vitro and in vivo analyses of mRNA expression

We previously identified high levels of Na(v)1.7 voltage-gated sodium channel alpha-subunit (VGSCalpha) mRNA and protein in human prostate cancer cells and tissues. Here, we investigated auxillary beta-subunit (VGSCbetas) expression. In vitro, the combined expression of all four VGSCbetas was significantly (approximately 4.5-fold) higher in strongly compared to weakly metastatic cells. This was mainly due to increased beta1-expression, which was under androgenic control. In vivo, beta1-beta4 mRNAs were detectable and their expression in CaP vs non-CaP tissues generally reflected the in vitro levels in relation to metastatic potential. The possible role(s) of VGSCbetas (VGSCalpha-associated and VGSCalpha-independent) in prostate cancer are discussed.

Are voltage-dependent ion channels involved in the endothelial cell control of vasomotor tone?

In the microcirculation, longitudinal conduction of vasomotor responses provides an essential means of coordinating flow distribution among vessels in a complex network. Spread of current along the vessel axis can display a regenerative component, which leads to propagation of vasomotor signals over many millimeters; the ionic basis for the regenerative response is unknown. We examined the responses to 10 s of focal electrical stimulation (30 Hz, 2 ms, 30 V) of mouse cremaster arterioles to test the hypothesis that voltage-dependent Na(+) (Na(v)) and Ca(2+) channels might be activated in long-distance signaling in microvessels. Electrical stimulation evoked a vasoconstriction at the site of stimulation and a spreading, nondecremental conducted dilation. Endothelial damage (air bubble) blocked conduction of the vasodilation, indicating an involvement of the endothelium. The Na(v) channel blocker bupivacaine also blocked conduction, and TTX attenuated it. The Na(v) channel activator veratridine induced an endothelium-dependent dilation. The Na(v) channel isoforms Na(v)1.2, Na(v)1.6, and Na(v)1.9 were detected in the endothelial cells of cremaster arterioles by immunocytochemistry. These findings are consistent with the involvement of Na(v) channels in the conducted response. BAPTA buffering of endothelial cell Ca(2+) delayed and reduced the conducted dilation, which was almost eliminated by Ni(2+), amiloride, or deletion of alpha(1H) T-type Ca(2+) (Ca(v)3.2) channels. Blockade of endothelial nitric oxide synthase or Ca(2+)-activated K(+) channels also inhibited the conducted vasodilation. Our findings indicate that an electrically induced signal can propagate along the vessel axis via the endothelium and can induce sequential activation of Na(v) and Ca(v)3.2 channels. The resultant Ca(2+) influx activates endothelial nitric oxide synthase and Ca(2+)-activated K(+) channels, triggering vasodilation.

Vasa recta voltage-gated Na+ channel Nav1.3 is regulated by calmodulin

Rat descending vasa recta (DVR) express a tetrodotoxin (TTX)-sensitive voltage-operated Na(+) (Na(V)) conductance. We examined expression of Na(V) isoforms in DVR and tested for regulation of Na(V) currents by calmodulin (CaM). RT-PCR in isolated permeabilized DVR using degenerate primers targeted to TTX-sensitive isoforms amplified a product whose sequence identified only Na(V)1.3. Immunoblot of outer medullary homogenate verified Na(V)1.3 expression, and fluorescent immunochemistry showed Na(V)1.3 expression in isolated vessels. Immunochemistry in outer medullary serial sections confirmed that Na(V)1.3 is confined to alpha-smooth muscle actin-positive vascular bundles. Na(V)1.3 possesses a COOH-terminal CaM binding motifs. Using pull-down assays and immunoprecipitation experiments, we verified that CaM binds to either full-length Na(V)1.3 or a GST-Na(V)1.3 COOH-terminal fusion protein. In patch-clamp experiments, Na(V) currents were suppressed by calmodulin inhibitory peptide (CIP; 100 nM) or the CaM inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide hydrochloride (W7). Neither CIP nor W7 altered the voltage dependence of pericyte Na(V) currents; however, raising electrode free Ca(2+) from 20 to approximately 2,000 nM produced a depolarizing shift of activation. In vitro binding of CaM to GST-Na(V)1.3C was not affected by Ca(2+) concentration. We conclude that Na(V)1.3 is expressed by DVR, binds to CaM, and is regulated by CaM and Ca(2+). Inhibition of CaM binding suppresses pericyte Na(V) currents.

Shear stress-induced shedding of soluble intercellular adhesion molecule-1 from saphenous vein endothelium

Within 6 h, shear stress upregulated intercellular adhesion molecule-1 (ICAM-1) (two- to four-fold, P<0.001) and induced matrix metalloproteinase-2 (MMP-2) in cultured human saphenous vein endothelial cells. By 8 h endothelial ICAM-1 levels returned to baseline, with concomitant increase in soluble ICAM-1 (sICAM-1) (P<0.001) and MMP-9 had been induced. Inclusion of a hydroxamate metalloproteinase inhibitor partially reversed the effects on ICAM-1 and sICAM-1 at 8 h, whereas TIMP-1, -2 or -3 had no effect. MMP-9, but not MMP-2, co-immunoprecipitated with ICAM-1. sICAM-1 was processed distal to Arg441, indicating that MMP-9, docking to ICAM-1, contributes to sICAM-1 shedding and attenuation of the shear stress-induced upregulation of ICAM-1.

Flow-dependent increase of ICAM-1 on saphenous vein endothelium is sensitive to apamin

The potassium channel blocker tetraethylammonium blocks the flow-induced increase in endothelial ICAM-1. We have investigated the subtype of potassium channel that modulates flow-induced increased expression of ICAM-1 on saphenous vein endothelium. Cultured human saphenous vein endothelial cells (HSVECs) or intact saphenous veins were perfused at fixed low and high flows in a laminar shear chamber or flow rig, respectively, in the presence or absence of potassium channel blockers. Expression of K(+) channels and endothelial ICAM-1 was measured by real-time polymerase chain reaction and/or immunoassays. In HSVECs, the application of 0.8 N/m(2) (8 dyn/cm(2)) shear stress resulted in a two- to fourfold increase in cellular ICAM-1 within 6 h (P < 0.001). In intact vein a similar shear stress, with pulsatile arterial pressure, resulted in a twofold increase in endothelial ICAM-1/CD31 staining area within 1.5 h (P < 0.001). Both increases in ICAM-1 were blocked by inclusion of 100 nM apamin in the vein perfusate, whereas other K(+) channel blockers were less effective. Two subtypes of small conductance Ca(2+)-activated K(+) channel (selectively blocked by apamin) were expressed in HSVECs and vein endothelium (SK3>SK2). Apamin blocked the upregulation of ICAM-1 on saphenous vein endothelium in response to increased flow to implicate small conductance Ca(2+)-activated K(+) channels in shear stress/flow-mediated signaling pathways.

Therapy and prophylaxis of inhaled biological toxins

This review highlights the current lack of therapeutic and prophylactic treatments for use against inhaled biological toxins, especially those considered as potential biological warfare (BW) or terrorist threats. Although vaccine development remains a priority, the use of rapidly deployable adjunctive therapeutic or prophylactic drugs could be life-saving in severe cases of intoxication or where vaccination has not been possible or immunity not established. The current lack of such drugs is due to many factors. Thus, methods involving molecular modelling are limited by the extent to which the cellular receptor sites and mode of action and structure of a toxin need to be known. There is also our general lack of knowledge of what effect individual toxins will have when inhaled into the lungs - whether and to what extent the action will be cell specific and cytotoxic or rather an acute inflammatory response requiring the use of immunomodulators. Possible sources of specific high-affinity toxin antagonists being investigated include monoclonal antibodies, selected oligonucleotides (aptamers) and derivatized dendritic polymers (dendrimers). The initial selection of suitable agents of these kinds can be made using cytotoxicity assays involving cultured normal human lung cells and a range of suitable indicators. The possibility that a mixture of selected antibody, aptamer or dendrimer-based materials for one or more toxins could be delivered simultaneously as injections or as inhaled aerosol sprays should be investigated.

Generation and characterisation of human saphenous vein endothelial cell lines

Primary human endothelial cells have a finite life span in vitro. After 3-4 passages, they tend to de-differentiate and eventually reach senescence. This limits their use in studies of endothelial cell function. To overcome this, we have developed human saphenous vein endothelial cell lines (HSVEC lines). Two cell lines were produced by infection with pZipSVtsA58-U19 which encodes the simian virus 40 large T-antigen, and one cell line was obtained by transfection with pLXSN16E6E7, which encodes the human papillomavirus type 16 E6 and E7 genes. Two of the three HSVEC lines exhibited an extended life span in vitro and retained characteristic endothelial "cobblestone" morphology. These cell lines expressed the known endothelial markers CD31 and vascular endothelial cadherin, and were able to bind Ulex europaeus lectin I, but they did not retain the expression of von Willebrand factor. Furthermore, one cell line was able to functionally up-regulate the expression of intercellular adhesion molecule-1 in response to stimulation with tumor necrosis factor alpha and was also able to incorporate acetylated low-density lipoprotein. Our results suggest that this latter HSVEC line will provide a useful resource to investigate selected responses of the vascular endothelium to physiological and pathological situations.

Interaction of fibrinogen with saphenous vein endothelial cells stimulates tyrosine phosphorylation of cortactin

Fibrinogen can engage diverse receptors on vascular cells, including ICAM-1. We have investigated the effect of fibrinogen on the tyrosine phosphorylation of cortactin, a cytoskeletal protein in human saphenous vein endothelial cells (HSVECs). Incubation of HSVECs with fibrinogen (0-4 microM) caused a concentration-dependent increase in the tyrosine phosphorylation of cortactin. Fibrinogen (4 microM) and fibrinogen fragment D (4 microM) caused 250% and >450% increase in tyrosine phosphorylation of cortactin respectively, but fibrinogen fragment E (50 kDa form) was ineffective. Preincubation of HSVECs with soluble ICAM-1 attenuated the response to fibrinogen. At physiological concentrations fibrinogen binds to receptors (probably including ICAM-1) on HSVECs, to increase tyrosine phosphorylation of cortactin.

Regulation by fibrinogen and its products of intercellular adhesion molecule-1 expression in human saphenous vein endothelial cells

It has been reported that fibrinogen may act as a bridging ligand, binding to intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells and to Mac-1 on THP-1 cells (a monocytic cell line) to increase adhesion. In this study, we investigated whether fibrinogen altered the expression of ICAM-1 and, thus, increased the adhesion of THP-1 cells to cultured human saphenous vein endothelial cells (HSVECs). Incubation of HSVECs with 0.3 to 4 micromol/L fibrinogen caused a time- and concentration-dependent increase in ICAM-1, as determined by ELISA. The 4- to 5-fold increase in ICAM-1 protein concentration in HSVECs stimulated by 4 micromol/L fibrinogen for 6 hours was concomitant with a 4- to 5-fold increase in ICAM-1 mRNA. This fibrinogen-stimulated ICAM-1 upregulation was associated with a 2-fold increase in THP-1 cell adhesion to HSVECs. The fibrinogen-derived peptide Bbeta15-42 bound to HSVECs (K(d) 0.18 micromol/L). Preincubation of HSVECs with Bbeta15-42, a neutralizing antibody to urokinase plasminogen activator (uPA), or the F(ab)(1) fragment of a monoclonal antibody to vascular endothelial cadherin significantly attenuated the increase in ICAM-1 stimulated by fibrinogen. Capillary electrophoretic analysis indicated that anti-uPA prevented the release of any fibrinopeptide B (Bbeta1-14) in cultures of HSVECs incubated with 4 micromol/L fibrinogen for 6 hours. Moreover, incubation of HSVECs with either fibrin monomer (1 micromol/L) or monoclonal antibodies to vascular endothelial cadherin (25 microg/mL) increased ICAM-1 protein concentration 3- to 4-fold. These findings indicate that cleavage of fibrinopeptide B from fibrinogen by endothelial uPA permits the exposed Bbeta15-42 sequence of fibrinogen to bind to vascular endothelial cadherin on HSVECs and to upregulate the expression of ICAM-1.

Shear stress-mediated extracellular signal-regulated kinase activation is regulated by sodium in endothelial cells. Potential role for a voltage-dependent sodium channel

Fluid shear stress is an important regulator of endothelial cell (EC) function. To determine whether mechanosensitive ion channels participate in the EC response to shear stress, we characterized the role of ion transport in shear stress-mediated extracellular signal-regulated kinase (ERK1/2) stimulation. Replacement of all extracellular Na+ with either N-methyl-D-glucamine or choline chloride increased the ERK1/2 stimulation in response to shear stress by 1.89 +/- 0.1-fold. The Na+ effect was concentration-dependent (maximal effect, </=12.5 mM) and was specific for shear stress-mediated ERK1/2 activation as epidermal growth factor-stimulated ERK1/2 activation was unaffected by removal of extracellular Na+. Shear stress-mediated ERK1/2 activation was potentiated by the voltage-gated sodium channel antagonist, tetrodotoxin (100 nM), to a magnitude similar to that achieved with extracellular Na+ withdrawal. Transfection of Chinese hamster ovary cells with a rat brain type IIa voltage-gated sodium channel completely inhibited shear stress-mediated ERK1/2 activation in these cells. Inhibition was reversed by performing the experiment in sodium-free buffer or by including tetrodotoxin in the buffer. Western blotting of bovine and human EC lysates with SP19 antibody detected a 250-kDa protein consistent with the voltage-gated sodium channel. Degenerate polymerase chain reaction of cDNA from primary human EC yielded transcripts whose sequences were identical to the sodium channel SCN4a and SCN8a alpha subunit genes. These results indicate that shear stress-mediated ERK1/2 activation is regulated by extracellular sodium and demonstrate that ion transport via Na+ channels modulates EC responses to shear stress.