Contraction Of Basilar Artery Research Articles

Inhibitory effects of eicosapentaenoic acid (EPA) on contractions in pig basilar and coronary arteries

Inhibitory effects of eicosapentaenoic acid (EPA) on contractions in pig basilar and coronary arteries

Docosahexaenoic acid inhibits U46619- and prostaglandin F2α-induced pig coronary and basilar artery contractions by inhibiting prostanoid TP receptors

Docosahexaenoic acid (DHA, an n-3 polyunsaturated fatty acid) inhibits U46619 (a TP receptor agonist)- and prostaglandin F2α-induced contractions in rat aorta and mesenteric arteries. However, whether these effects could be replicated in vasospasm-prone vessels, such as coronary and cerebral arteries, remains unknown. Here, we evaluated the changes in pig coronary and basilar artery tensions and intracellular Ca2+ concentrations in human prostanoid TP or FP receptor-expressing cells. We aimed to clarify whether DHA inhibits U46619- and prostaglandin F2α-induced contractions in spasm-prone blood vessels and determine if the TP receptor is the primary target for DHA. In both pig coronary and basilar arteries, DHA suppressed U46619- and prostaglandin F2α-induced sustained contractions in a concentration-dependent manner, but did not affect contractions induced by 80 mM KCl. SQ 29,548 (a TP receptor antagonist) suppressed U46619- and prostaglandin F2α-induced contractions by approximately 100% and 60%, respectively. DHA suppressed both U46619- and prostaglandin F2α-induced increases in intracellular Ca2+ concentrations in human TP receptor-expressing cells. However, DHA did not affect prostaglandin F2α-induced increases in intracellular Ca2+ concentrations in human FP receptor-expressing cells. These findings suggest that DHA potently inhibits TP receptor-mediated contractions in pig coronary and basilar arteries, and the primary mechanism underlying its inhibitory effects on arterial contractions involves inhibiting TP receptors.

The role of total flavone of Camellia on cerebrovascular vasopasm after subarachnoid hemorrhage in rats

Background: This study was undertaken to explore the role of total flavones of Camellia (TFC) on the cerebrovascular dysfunction in rats after experimental subarachnoid hemorrhage (SAH). Materials and Methods: The contraction and dilation of cerebral basilar artery (BA), nitric oxide (NO) level, and nitric oxide synthase (NOS) activity in rat serum and the expression of endothelial NOS (eNOS) in cerebral vessels were measured. Furthermore, the effect of potassium channel blockers, endothelium removal, L-NG-nitroarginine methyl ester (L-NAME), or prostacyclin I2 (PG I2) production inhibitor on the response of isolated BA derived from normal rats was also evaluated to explore the underlying mechanism of vasodilation induced by total flavones. Results: The contraction of rat BA to U46619 markedly increased and the vasodilation to acetylcholine remarkably reduced after SAH. Interestingly, these vascular dysfunctions were profoundly ameliorated by pretreatment of TFC. Moreover, total flavones could induce a concentration-dependent relaxation in isolated BA from normal rats, which was obviously eliminated by co-application of potassium channel blockers, ChTx and Apamin, application of L-NAME, or endothelial removal. In addition, total flavones pretreatment obviously improved the expression of eNOS in BA, serum NO level, and NOS activity at 48 h after SAH. Conclusion: These findings revealed that TFC has protective effect on cerebrovascular dysfunction after SAH and demonstrated that the protection could be due to its upregulation of eNOS expression and activation of potassium channel.

A novel antihypertension agent, sargachromenol D from marine brown algae, Sargassum siliquastrum, exerts dual action as an L-type Ca2+ channel blocker and endothelin A/B2 receptor antagonist

We isolated the novel vasoactive marine natural products, (5E,10E)-14-hydroxy-2,6,10-trimethylpentadeca-5,10-dien-4-one (4) and sargachromenol D (5), from Sargassum siliquastrum collected from the coast of the East Sea in South Korea by using activity-guided HPLC purification. The compounds effectively dilated depolarization (50mMK+)-induced basilar artery contraction with EC50 values of 3.52±0.42 and 1.62±0.63μM, respectively, but only sargachromenol D (5) showed a vasodilatory effect on endothelin-1 (ET-1)-induced basilar artery contraction (EC50=9.8±0.6μM). These results indicated that sargachromenol D (5) could act as a dual antagonist of l-type Ca2+ channel and endothelin A/B2 receptors. Moreover, sargachromenol D (5) lowered blood pressure in spontaneous hypertensive rats (SHRs) 2h after oral treatment at a dose of 80mg/kg dose and the effect was maintained for 24h. Based on our ex vivo and in vivo experiments, we propose that sargachromenol D (5) is a strong candidate for the treatment of hypertension that is not controlled by conventional drugs, in particular, severe-, type II diabetes-, salt-sensitive, and metabolic disease-induced hypertension.

Synthesis of alkylsulfonyl and substituted benzenesulfonyl curcumin mimics as dual antagonist of L-type Ca2+ channel and endothelin A/B2 receptor

We synthesized a library of curcumin mimics with diverse alkylsulfonyl and substituted benzenesulfonyl modifications through a simple addition reaction of important intermediate, 1-(3-Amino-phenyl)-3-(4-hydroxy-3-methoxy-phenyl)-propenone (10), with various sulfonyl chloride reactants and then tested their vasodilatation effect on depolarization (50mM K+)- and endothelin-1 (ET-1)-induced basilar artery contraction. Generally, curcumin mimics with aromatic sulfonyl groups showed stronger vasodilation effect than alkyl sulfonylated curcumin mimics. Among the tested compounds, six curcumin mimics (11g, 11h, 11i, 11j, 11l, and 11s) in a depolarization-induced vasoconstriction and seven compounds (11g, 11h, 11i, 11j, 11l, 11p, and 11s) in an ET-1-induced vasoconstriction showed strong vasodilation effect. Based on their biological properties, synthetic curcumin mimics can act as dual antagonist scaffold of L-type Ca2+ channel and endothelin A/B2 receptor in vascular smooth muscle cells. In particular, compounds 11g and 11s are promising novel drug candidates to treat hypertension related to the overexpression of L-type Ca2+ channels and ET peptides/receptors-mediated cardiovascular diseases.

Characterization of the contractile P2Y14 receptor in mouse coronary and cerebral arteries

Extracellular UDP-glucose can activate the purinergic P2Y14 receptor. The aim of the present study was to examine the physiological importance of P2Y14 receptors in the vasculature. The data presented herein show that UDP-glucose causes contraction in mouse coronary and basilar arteries. The EC50 values and immunohistochemistry illustrated the strongest P2Y14 receptor expression in the basilar artery. In the presence of pertussis toxin, UDP-glucose inhibited contraction in coronary arteries and in the basilar artery it surprisingly caused relaxation. After organ culture of the coronary artery, the EC50 value decreased and an increased staining for the P2Y14 receptor was observed, showing receptor plasticity.

Bradykinin induces NO and PGF2α production via B2 receptor activation from cultured porcine basilar arterial endothelial cells.

Our previous in vitro study demonstrated that bradykinin (BK) induced relaxation and contraction of porcine basilar artery (PBA) mediated via activation of endothelial B2 receptors. The main relaxing and contracting factors appeared to be nitric oxide (NO) and prostaglandin (PG) H2, respectively, but not thromboxane A2. After obtaining these findings, we succeeded in cultivating endothelial cells isolated from the PBA. Although PGH2 has different functionally active isoforms, including PGD2, PGE2, and PGF2α, we have not yet clarified which of them is responsible for BK-induced contraction. Therefore, we attempted to quantify NO and PG production from cultured porcine basilar arterial endothelial cells (PBAECs) and to identify which of the PGs was involved in this contraction. The cultured PBAECs produced NO spontaneously, and BK enhanced this production in a concentration-dependent manner. The NO synthase inhibitor Nω-nitro-L-arginine (L-NNA) and the B2 receptor antagonist HOE-140, but not the B1 receptor antagonist des-Arg(9), [Leu(8)]-BK, completely abolished it. In a functional study, PGD2, PGE2, and PGF2α induced concentration-dependent contractions in isolated porcine basilar arterial rings, the order of maximum contraction being PGF2α > PGE2 > PGD2. The cultured PBAECs produced PGD2, PGE2, and PGF2α spontaneously, and BK significantly enhanced the production of PGF2α, but not that of PGD2 and PGE2. The B2, but not B1, antagonist completely abolished the BK-enhanced production of PGF2α. These results suggest that BK induces production of NO and PGF2α simultaneously from PBAECs via B2 receptor activation.

EndothelinA–endothelinB receptor cross-talk in rat basilar artery in situ

The rationale for the therapeutic use of dual as opposed to selective endothelin (ET) receptor antagonists stems in part from cross-talk between the ET(A) and ET(B) receptors. However, whether ET(A)-ET(B) receptor cross-talk is present in the cerebral vasculature is difficult to discern since findings of cross-talk contrast even among the few reports available. Thus, this study tested whether ET(A)-ET(B) receptor cross-talk is present in the rat basilar artery. In an in situ cranial window, 0.1μM sarafotoxin S6c, an ET(B) receptor agonist, relaxed basilar artery basal tone by 54%. ET-1 (3nM) in the absence and presence of 10μM BQ123, an ET(A) receptor agonist, induced 13% contraction and 15% relaxation, respectively. In contrast, the 3-nM ET-1 plateau contraction was relaxed by only ∼50% by 3-10μM BQ123 and 10μM BQ610, ET(A) receptor antagonists. N(ω)-nitro-L: -arginine, an NO synthase inhibitor, did not enhance contraction to 3nM ET-1, suggesting that the partial relaxation of the ET-1 plateau contraction did not involve unmasked endothelial ET(B) receptor-mediated relaxation. The ∼50% ET-1 contraction that remained following ET(A) receptor antagonist was relaxed by 3-10μM BQ788, consistent with an ET(B) receptor-mediated component of contraction. However, 10μM BQ788 in the absence of prior ET(A) receptor antagonist did not cause relaxation. Subsequent BQ123 addition in the presence of BQ788 completely relaxed the ET-1 contraction. PD145065 (1μM), an ET(A/B) receptor antagonist, completely relaxed 3-nM ET-1 contracted vessels in both the absence and presence of BQ123. These findings suggest that the inability of ET(A) receptor antagonist to completely relax the ET-1 plateau contraction in rat basilar artery is due to ET(A)-ET(B) receptor cross-talk.

Altered expression of connexin43 and its possible role in endothelin - 1 - induced contraction in rabbit basilar artery

Objective To investigate the role of connexin43 in ET- 1 -induced contraction in rabbit basilar artery.Methods The ET - 1 - induced contraction without or with carbenoxolone was studied with an isometric tension system.The expression of connexin43 protein in ET - t stimulated basilar arteries was studied with Western blot.Scrape/scratch method was used to analyze the function of gap junction in cultured rabbit cerebrovascular smooth muscle ceils.Results ET - 1 produced a concentration - dependent contraction.Carbenoxolone inhibited ET- 1 induced contraction.The connexin43 protein level was increased in ET- 1stimulated basilar arteries.Carbenoxolone decreased the connexin43 protein level increased by ET - 1.Cells treated with ET - 1 appeared positive communication and the dye transfer was increased in a time - dependent fashion.Carbenoxolone suppressed the ET - 1 - induced increasement of dye transfer.Conclusions The enhancement of gap junction intercellular communication is activated by ET - 1 via modulating the expression of connexin43,and plays an important role in the pathogenesis of cerebral vasospasm.Inhibition of vascular GJIC as a means of reducing cerebral vasospasm after SAH may have therapeutic advantage. Key words: Connexin43 ; Gap junction ; ET - 1 ; Cerebral vasospasm

Alterations in vasoconstrictor responses to the endothelium-derived contracting factor uridine adenosine tetraphosphate are region specific in DOCA-salt hypertensive rats

Uridine adenosine tetraphosphate (Up 4A) has been recently identified as a novel and potent endothelium-derived contracting factor and contains both purine and pyrimidine moieties, which activate purinergic P2X and P2Y receptors. The present study was designed to compare contractile responses to Up 4A and other nucleotides such as ATP (P2X/P2Y agonist), UTP (P2Y 2/P2Y 4 agonist), UDP (P2Y 6 agonist), and α,β-methylene ATP (P2X 1 agonist) in different vascular regions [thoracic aorta, basilar, small mesenteric, and femoral arteries] from deoxycorticosterone acetate-salt (DOCA-salt) and control rats. In DOCA-salt rats [vs. control uninephrectomized (Uni) rats]: (1) in thoracic aorta, Up 4A-, ATP-, and UTP-induced contractions were unchanged; (2) in basilar artery, Up 4A-, ATP-, UTP- and UDP-induced contractions were increased, and expression for P2X 1, but not P2Y 2 or P2Y 6 was decreased; (3) in small mesenteric artery, Up 4A-induced contraction was decreased and UDP-induced contraction was increased; expression of P2Y 2 and P2X 1 was decreased whereas P2Y 6 expression was increased; (4) in femoral artery, Up 4A-, UTP-, and UDP-induced contractions were increased, but expression of P2Y 2, P2Y 6 and P2X 1 was unchanged. The α,β-methylene ATP-induced contraction was bell-shaped and the maximal contraction was reached at a lower concentration in basilar and mesenteric arteries from Uni rats, compared to arteries from DOCA-salt rats. These results suggest that Up 4A-induced contraction is heterogenously affected among various vascular beds in arterial hypertension. P2Y receptor activation may contribute to enhancement of Up 4A-induced contraction in basilar and femoral arteries. These changes in vascular reactivity to Up 4A may be adaptive to the vascular alterations produced by hypertension.

Mitochondrial monoamine oxidase‐A‐mediated hydrogen peroxide generation enhances 5‐hydroxytryptamine‐induced contraction of rat basilar artery

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies. Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC(50) : 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca(2+) -activated K(+) (BK(Ca) ) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF(-1) vs. 2.61 ± 0.66 pA·pF(-1) ). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK(Ca) amplitude than in those from WKY. 5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK(Ca) gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.

Characterization of bradykinin‐induced endothelium‐independent contraction in equine basilar artery

We investigated the effect of bradykinin (BK) on isolated equine basilar arterial rings with and without endothelium. BK induced concentration-dependent contraction of resting arterial rings and no relaxation when the rings were precontracted by prostaglandin F(2alpha). The maximal response and pD(2) value were 161.2 +/- 28.1% (to 60 mm KCl-induced contraction) and 8.24 +/- 0.25 respectively. The cumulative concentration-response curve for BK was not shifted to the right by des-Arg(9)-[Leu(8)]-BK (a B(1)-receptor antagonist), HOE140 (a B(2)-receptor antagonist) or NPC567 (another B(2)-receptor antagonist). In four of six basilar arteries, NPC567 induced concentration-dependent contraction. Indomethacin (a cyclooxygenase inhibitor), nordihydroguaiaretic acid (a lipoxygenase inhibitor), quinacrine (a phospholipase A(2) inhibitor), tetrodotoxin (a selective blocker of Na(+) channels), guanethidine (a nor-adrenergic neuron blocking drug), phentolamine (an alpha-adrenoceptor antagonist), Nomega-nitro-L-arginine (L-NNA, a nitric oxide (NO) synthase inhibitor) and endothelial denudation did not affect the BK-induced contraction. L-NNA and indomethacin induced contraction and relaxation under resting vascular tone respectively. These results suggest that endothelial cells are not involved in BK-induced contraction and that the contraction is not mediated via activation of known B(1) and B(2) receptors. Arachidonic acid metabolites and neurotransmitters like norepinephrine and NO might not play a role in BK-induced contraction in equine basilar artery.

Altered expression of connexin43 and its possible role in endothelin-1-induced contraction in rabbit basilar artery

Background and purpose: Endothelin-1 (ET-1) plays an important role in the pathogenesis of cerebral vasospasm. Gap junction participates in the pathologic processes of cerebrovascular diseases and may play an important role. The aim of this study is to investigate the role of connexin43 in ET-1-induced contraction in rabbit basilar artery.Methods: The ET-1-induced contraction without or with carbenoxolone was studied with an isometric tension system. Expression of connexin43 protein in ET-1–stimulated basilar arteries was studied with Western blot. Scrape/scratch method was used to analyse the function of gap junction in cultured rabbit cerebrovascular smooth muscle cells.Results: (1) ET-1 produced a concentration-dependent contraction. Carbenoxolone inhibited ET-1-induced contraction; (2) connexin43 protein level is increased in ET-1-stimulated basilar arteries. Carbenoxolone decreases the connexin43 protein level increased by ET-1; (3) cells treated with ET-1 appeared positive communicate and the dye transfer was increased in a time-dependent fashion; 4 carbenoxolone suppressed the ET-1-induced increases in dye transfer.Conclusion: The enhancement of gap junction intercellular communication is activated by ET-1 via modulating the expression of connexin43, and plays an important role in the pathogenesis of cerebral vasospasm. Inhibiting vascular GJIC as a means of reducing cerebral vasospasm after SAH may be of therapeutic advantage.

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

A novel approach for the determination of contractile and calcium responses of the basilar artery employing real-time confocal laser microscopy

Introduction Intracellular calcium concentration ([Ca 2+] i) modifications in endothelial and smooth muscle cells represent a key element in the pathogenesis of cerebral artery vasospasm. Therefore, the present study documented potential application of confocal laser microscopy in the determination of contractile and [Ca 2+] i responses in basilar artery. Methods Experiments were performed on the rat isolated basilar artery. Changes in [Ca 2+] i were determined by ratiometry involving Fluo-4/AM and Fura Red/AM. Contractile function was calculated from the change in fluorescent area by Fluo-4/AM. Results KCl (50 mM) elicited an increase in [Ca 2+] i and contraction in basilar artery; moreover, nearly well maintained responses were evident for at least 120 min following the first application. 10 μM 5-hydroxytryptamine (5-HT), 10 μM α,β-methyleneadenosine 5′-triphosphate (α,β-meATP) and 10 nM vasopressin (VP) also induced increases in [Ca 2+] i and contraction dose-dependently. Additionally, 10 μM acetylcholine elicited a transient [Ca 2+] i decrease and sustained relaxation. In individual cells, rhythmical changes in [Ca 2+] i were observed after 10 μM 5-HT. VP (10 nM) evoked modest Ca 2+ oscillation in individual cells; however, Ca 2+ oscillation was not detectable with 10 μM α,β-meATP. Discussion These results indicate that this method offers reproducibility and quantifiable effects. Imaging technology may therefore be applied to the estimation of [Ca 2+] i responses at the tissue level as well as at the level of the individual cell. Thus, confocal laser microscopy is a suitable tool for estimation of small artery function.

Involvement of phospholipase C in endothelin 1–induced stimulation of Ca++ channels and basilar artery contraction in rabbits

Endothelin 1 (ET-1) is a major cause of cerebral vasospasm after subarachnoid hemorrhage (SAH), and extracellular Cal++ influx plays an essential role in ET-1-induced vasospasm. The authors recently demonstrated that ET-1 activates two types of Ca"-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) and a store-operated Cal++ channel (SOCC) in vascular smooth-muscle cells located in the basilar arteries (BAs) of rabbits. In the present study, they investigate the effects of phospholipase C (PLC) on ET-1-induced activation of these Ca++ channels and BA contraction by using the PLC inhibitor U73122. Methods. To determine which Cal++ channels are activated via a PLC-dependent pathway, these investigators monitored the intracellular free Cal++ concentration ([Ca++]i). The role of PLC in ET-1-induced vascular contraction was examined by performing a tension study of rabbit BA rings. The U73122 inhibited the ET-1-induced transient increase in [Ca++]i, which resulted from mobilization of Ca++ from the intracellular store. Phospholipase C also inhibited ET-1-induced extracellular Ca++ influx through the SOCC and NSCC-2, but not through the NSCC-1. The U73122 inhibited the ET-1-induced contraction of the rabbit BA rings, which depended on extracellular Cal++ influx through the SOCC and NSCC-2. Conclusions. These results indicate the following. (1) The SOCC and NSCC-2 are stimulated by ET-1 via a PLC-dependent cascade whereas NSCC-1 is stimulated via a PLC-independent cascade. (2) The PLC is involved in the ET-1-induced contraction of rabbit BA rings, which depends on extracellular Ca++ influx through the SOCC and NSCC-2.

Modulatory effect of interleukin-1β on rat isolated basilar artery contraction

An increased level of cytokine interleukin-1 (IL-1) has been detected around the site of stroke. However, the effect of IL-1β on the basilar artery has received little attention. We evaluated the effects of IL-1β on the contractile response of rat isolated basilar artery by measuring isometric tension change. IL-1β (10 ng/ml) and phenylephrine (0.1 nM) markedly enhanced U46619 (30 and 100 nM)-induced basilar artery contraction. The IL-1β-mediated potentiation was partly suppressed by zinc protoporphyrin (3 μM) and was abolished by tetrodotoxin (TTX, 100 nM), (−)-perillic acid (1 μM), PD98059 (0.3 μM), SB203580 (1 μM) and prazosin (1 μM). Our data suggest that IL-1β (10 ng/ml) causes an enhancement of U46619-mediated basilar artery contraction that probably involves TTX-sensitive neuronal release of an α 1-adrenoceptor agonist and activation of p42/p44 and p38 mitogen-activated protein kinases/p21 ras pathways.

The importance of extracellular calcium for endothelin type A and B receptor-mediated contraction in rat basilar artery

The importance of extracellular calcium for endothelin type A and B receptor-mediated contraction in rat basilar artery

Chloride Efflux is Involved in ET-1 and 5-HT-Induced Contraction in Rabbit Basilar Artery

Chloride (Cl-) efflux induces depolarization and contributes to contraction of cerebral arteries. We tested the effect of endothelin-1 and 5-hydroxytryptamine on isometric tension in rabbit basilar artery by inhibition of Na+-K+-2Cl- co-transporter and Cl-/HCO3- exchanger to decrease Cl-, by decreasing extracellular Cl- concentration, and by blocking Cl- channels using Cl- channel inhibitors. We have made the following observations: (i)endothelin-1 and 5-hydroxytryptamine produced contraction in the normal Cl- Krebs-Henseleit bicarbonate solution (123 mM Cl-); (ii)inhibition of Na+-K+-2Cl- co-transporter with bumetanide abolished the contractions; (iii) bicarbonate-free solution with HEPES reduced contractions to 5-hydroxytryptamine and endothelin-1; (iv) substitution of extracellular Cl- with methanesulfonate acid (MS- 113 mM, Cl- 10 mM) enhanced peak contraction to 5-hydroxytryptamine and endothelin-1 and decreased plateau contraction to 5-hydroxytryptamine, but did not affect the plateau contraction to endothelin-1 and KCl; and (v) blockade of Ca2+-dependent Cl- channel with niflumic acid and non-selective Cl- channel with 5-nitro-2-(3-phenylpropylamino) benzoic acid and indanyloxyacetic acid-94, R- (+)-methylindazone (R- (+)-IAA-94)decreased contractions to endothelin-1 and 5-hydroxytryptamine.However, removal of endothelium attenuated the effect of Cl-channel inhibitors. In conclusion, Cl- channels and Cl- flux are involved in endothelin-1-induced and 5-hydroxytryptamine-induced contraction in rabbit basilar artery. Cl- channel blockers might exert additional effects by releasing vasodilatation agents from endothelial cells.

Mechanisms underlying diabetes enhancement of endothelin-1-induced contraction in rabbit basilar artery

The influence of alloxan-induced diabetes on the reactivity of rabbit basilar artery to endothelin-1 was examined. Endothelin-1 induced concentration-dependent contraction of basilar arteries that was higher in diabetic than in control rabbits. Endothelium removal produced a higher enhancement of the endothelin-1-induced contraction in control than in diabetic rabbits. N G-nitro- l-arginine ( l-NOArg) enhanced the maximal contraction induced by endothelin-1 in control rabbits and potentiated this response in diabetic rabbits. Endothelin ET A receptor antagonist, cyclo( d-Asp-Pro- d-Val-Leu- d-Trp) (BQ-123), inhibited endothelin-1-induced contraction in both rabbit groups. Endothelin ET B receptor antagonist, 2,6-Dimethylpiperidinecarbonyl-γ-Methyl-Leu-N in-(Methoxycarbonyl)- d-Trp- d-Nle (BQ-788), enhanced endothelin-1-induced contraction in control rabbits and decreased the potency of endothelin-1 in diabetic rabbits. Sodium nitroprusside-induced relaxation of basilar arteries was lower in diabetic than in control rabbits. These results suggest that mechanisms underlying rabbit basilar artery hyperreactivity to endothelin-1 include decreased endothelial modulation of endothelin-1-induced contraction, with impaired endothelial endothelin ET B receptor activity; decreased sensitivity to nitric oxide (NO) in vascular smooth muscle; and enhanced participation of muscular endothelin ET A and ET B receptors.