Role of mitogen-activated protein kinase pathway in acetylcholine-mediated in vitro relaxation of rat pulmonary artery

In utero hypoxia attenuated acetylcholine-mediated vasodilatation via CHRM3/p-NOS3 in fetal sheep MCA: role of ROS/ERK1/2

Hypoxia can lead to adult middle cerebral artery (MCA) dysfunction and increase the risk of cerebrovascular diseases. It is largely unknown whether intrauterine hypoxia affects fetal MCA vasodilatation. This study investigated the effects and mechanisms of intrauterine hypoxia on fetal MCA vasodilatation. Near-term fetal sheep were exposed to intrauterine hypoxia. Human umbilical vein endothelial cells (HUVECs) were exposed to hypoxia in cellular experiments. Vascular tone measurement, molecular analysis, and transmission electron microscope (TEM) were utilized to determine vascular functions, tissue anatomy, and molecular pathways in fetal MCA. In fetal MCA, acetylcholine (ACh) induced reliable relaxation, which was markedly attenuated by intrauterine hypoxia. Atropine, P-F-HHSiD, L-NAME, and u0126 blocked most ACh-mediated dilation, while AF-DX 116 and tropicamide partially inhibited the dilation. Indomethacin and SB203580 did not significantly change ACh-mediated dilation. Tempol and PS-341 could restore the attenuated ACh-mediated vasodilatation following intrauterine hypoxia. The mRNA expression levels of CHRM2 and CHRM3 and the protein levels of CHRM3, p-NOS3, SOD2, ERK1/2, p-ERK1/2, MAPK14, and p-MAPK14 were significantly reduced by intrauterine hypoxia. The dihydroethidium assay showed that the production of ROS was increased under intrauterine hypoxia. TEM analysis revealed endothelial cells damaged by intrauterine hypoxia. In HUVECs, hypoxia increased ROS formation and decreased the expression of CHRM3, p-NOS3, SOD1, SOD2, SOD3, ERK1/2, p-ERK1/2, and p-MAPK14, while tempol and PS-341 potentiated p-NOS3 protein expression. In conclusion, in utero hypoxia reduced ACh-mediated vasodilatation in ovine MCA predominantly via decreased CHRM3 and p-NOS3, and the decreased NOS3 bioactivities might be attributed to ROS and ERK1/2.

Functional characterization of the muscarinic receptors involved in endothelium-dependent relaxation in isolated canine uterine artery

Acetylcholine interacts with endothelial muscarinic receptors releasing nitric oxide and causing vasodilatation. To identify the receptor subtype responsible for acetylcholine-induced relaxation in canine uterine artery, the usual organ bath method for in vitro investigation on isolated blood vessels was applied. Using a range of muscarinic receptor antagonists such as atropine (nonselective), pirenzepine (M(1)-selective), methoctramine (M(2)-selective) and p-fluoro-hexahydro-sila-difenidol (p-FHHSiD) (M(1)/M(3)) and determining pA2 value of those antagonists through Shild analysis, we aimed at establishing a precise receptor mechanism underlying acetylcholine-induced relaxation in isolated canine uterine artery. The relaxation of uterine arterial rings in response to acetylcholine in the presence or absence of selective muscarinic receptors antagonists was calculated using concentration response curves. Acetylcholine induced concentration-dependent and endothelium-dependent relaxation of arterial rings precontracted with phenylephrine (pEC(50) = 6.90 +/- 0.02). Muscarinic receptors antagonists atropine, pirenzepine, methoctramine and p-FHHSiD competitively antagonized the response to acetylcholine and obtained pA(2) values were 9.91 +/- 0.06, 6.60 +/- 0.04, 6.21 +/- 0.08 and 8.05 +/- 0.1, respectively. This study showed that acetylcholine induced endothelium-dependent relaxation of canine uterine artery by stimulation of muscarinic receptors localized on the endothelial cells. On the basis of differential antagonist affinity, we suggest that the muscarinic receptors involved in the acetylcholine-induced relaxation of canine uterine artery are predominantly of M(3) subtype.

Acetylcholinesterase supports anchorage independence in colon cancer

Various roles have been attributed to Acetylcholinesterase (AChE) in cancer. Evidence exists for a pro-apoptotic function, consistent with a protective role of AChE. Because other reports suggested that upregulated AChE in some tumors may control cell adhesion, we tested the effects of AChE on anchorage independence (an essential component of metastasis) of colon tumor cells. Several AChE inhibitors dose-dependently suppressed colony formation of HTB-38 cells in soft agar. This effect of AChE was confirmed with HTB-38 cells stably overexpressing AChE. In contrast, cell proliferation was not altered by the effective doses of these chemical inhibitors or by transfected AChE. Protection from cell cycle arrest consecutive to cancer cell detachment may be conveyed by changes in cell-matrix interactions. Reflective of such changes, the AChE overexpressing cells adhered more strongly to Fibronectin than did the vector controls. The AChE-dependent adhesion was RGD-dependent and accompanied by increased c-Myb DNA-binding, suggesting that AChE upregulates an Integrin receptor via c-Myb. In support of these observations, we find AChE message and protein to be expressed in a large fraction of colon cancers and in all colon tumor cell lines analyzed, but only rarely in normal colon specimens. Our results imply a dual role for AChE in colon cancer. While the anti-apoptotic effects of AChE may be protective against early stages of tumorigenesis, this gene product may support the later stages of transformation by enhancing anchorage independent growth. The induction of Integrins could render the cells independent of microenvironmental cues and override cell cycle arrest after deadhesion.

Tiotropium is less likely to induce oxygen desaturation in stable COPD patients compared to long-acting β2-agonists

In a three-way crossover pilot study, the acute effects of tiotropium 18 microg inhalation on the respiratory function and arterial blood gas tensions of 30 patients with stable chronic obstructive pulmonary disease (COPD) were compared with those of salmeterol 50 microg and formoterol 12 microg. In each study day, lung function and arterial blood gas analyses were performed before and up to 180 min after inhalation. All treatments significantly improved lung function, increased DLco, decreased PaO2, and increased P(A-a)O2, with no change in PaCO2. The effects of salmeterol and tiotropium on PaO2 were slower in onset and more prolonged than those of formoterol but PaO2AUC0-180 min was significantly greater for formoterol and salmeterol than for tiotropium. It is likely that the significant but small decreases in PaO2 and increases in P(A-a)O2 have been caused by pulmonary vasodilator effects. Since the three agents were similar in inducing bronchodilation, we believe that tiotropium is preferable in patients with hypoxemia caused by stable COPD because it seems to carry a smaller risk of worsening systemic hypoxemia.

Involvement of endothelial NO in the dilator effect of VIP on rat isolated pulmonary artery

The endothelium and its interaction with smooth muscle play a central role in the local control of the pulmonary vasculature, and endothelial dysfunction is thought to contribute to pulmonary hypertension and chronic obstructive pulmonary disease. Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, relaxes the rat pulmonary artery, but there is controversy as to whether or not this action of VIP depends on the endothelium. The aim of this study, therefore, was to investigate the role of the endothelium and nitric oxide (NO), the major endothelium-derived relaxing factor, in the dilator action of VIP on the rat isolated pulmonary artery. Pulmonary artery preparations pre-contracted by the alpha(1)-adrenoceptor agonist L-phenylephrine were relaxed by VIP (0.003-1 microM) and acetylcholine (0.003-10 microM) in a concentration-dependent manner. Mechanical removal of the endothelium reduced the maximal response to VIP by about 50% and practically abolished the response to acetylcholine. Inhibition of NO synthesis by N(omega)-nitro-L-arginine methyl ester (0.5 mM) had a similar effect, abolishing the vasorelaxation caused by acetylcholine and attenuating the vasorelaxation caused by VIP by about 50%. From these data it is concluded that the relaxant action of VIP on the rat isolated pulmonary artery depends in part on the presence of the endothelium and that this part is mediated by endothelial NO.

Activation of the iberiotoxin-sensitive BKCa channels by salvianolic acid B of the porcine coronary artery smooth muscle cells

In this study, we examined the effects of Salvia miltiorrhiza (Danshen) crude extract, some of its lipid-soluble components (tanshinone I, tanshinone II(A), cryptotanshinone, dihydroisotanshinone I) and the water-soluble compounds (danshensu and salvianolic acid B) on the K(+) channels such as the iberiotoxin-sensitive Ca(2+)-activated K(+) (BK(Ca)) channels and the glibenclamide-sensitive ATP-dependent K(+) (IK(ATP)) channels of the porcine left anterior descending coronary artery smooth muscle cells. Cumulative application of salvianolic acid B (30-300 microM) caused a l-NNA (100 microM)-insensitive, potentiation of the outward BK(Ca) current amplitude with no apparent effect on the IK(ATP) channels opening. Salvianolic acid B (300 microM) caused an ODQ (10 microM, a guanylate cyclase inhibitor)-sensitive enhancement of the outward BK(Ca) current amplitude. In contrast, none of the other isolated chemical constituents of S. miltiorrhiza modified the openings of the two types of K(+) channels studied. In conclusion, our results suggest that salvianolic acid B, a major hydrophilic constituent found in Radix S. miltiorrhiza, activated the opening of the BK(Ca) channels of the porcine coronary artery smooth muscle cells through the activation of guanylate cyclase without the involvement of the nitric oxide synthase activation.

Modulation by homocysteine of the iberiotoxin-sensitive, Ca2+ -activated K+ channels of porcine coronary artery smooth muscle cells

We evaluated the acute effect of homocysteine on the iberiotoxin-sensitive, Ca(2+)-activated K(+) (BK(Ca)) channels of the porcine coronary artery smooth muscle cells. NS 1619 (1 to 30 microM) caused a concentration-dependent enhancement of the BK(Ca) amplitude (recorded using the whole-cell, membrane-rupture configuration) only with an elevated [Ca(2+)](i) of approximately 444 nM, but not with [Ca(2+)](i) of approximately 100 nM. Homocysteine (30 microM) caused a small inhibition ( approximately 16%) of the BK(Ca) amplitude ([Ca(2+)](i)= approximately 444 nM), and a greater inhibition ( approximately 77%) was observed with 100 microM NADH present in the pipette solution. The inhibition persisted after washing. With NADPH (100 microM), a smaller magnitude of inhibition ( approximately 34%) of the BK(Ca) amplitude was recorded. The NS 1619-mediated enhancement of the BK(Ca) amplitude (with elevated [Ca(2+)](i) plus NADH in the pipette) was attenuated by homocysteine. The homocysteine-mediated inhibition of the BK(Ca) amplitude was suppressed by Tiron (10 mM) or diphenylene iodonium (30 nM), applied alone, but not by superoxide dismutase (500 U/ml) and catalase (500 U/ml). Generation of superoxide (O(2)(-)) of the smooth muscle cells (with NADH presence), measured using the lucigenin-enhanced chemiluminescence, was markedly increased by angiotensin II (100 nM) and homocysteine (30 microM). The chemiluminescence signal was sensitive to apocynin (300 microM) or Tiron, applied alone, but not to superoxide dismutase and catalase. In conclusion, our results demonstrate that acute homocysteine application inhibits the iberiotoxin-sensitive BK(Ca) channels (with elevated [Ca(2+)](i) and NADH present) which is probably caused by the NADH oxidase activation and the concomitant generation of intracellular superoxide.

Control by cholinergic mechanisms

In the respiratory tract acetylcholine is neurotransmitter in ganglia and postganglionic parasympathetic nerves, but in addition is paracrine mediator released from various non-neuronal cells. Almost every cell type present in the respiratory tract expresses nicotinic and muscarinic receptors and therefore appears to be a target for acetylcholine. The present review describes the mechanisms of synthesis and release of acetylcholine from neuronal and non-neuronal cells and the differential control mechanisms. The different cholinoceptors, multiple nicotinic and muscarinic receptors and their signalling are outlined and their involvement in the modulation of the function of various target cells, smooth muscles, nerves, surface epithelial, secretory cells, fibroblasts and inflammatory cells is discussed in detail.

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-1beta on the basilar artery has received little attention. We evaluated the effects of IL-1beta on the contractile response of rat isolated basilar artery by measuring isometric tension change. IL-1beta (10 ng/ml) and phenylephrine (0.1 nM) markedly enhanced U46619 (30 and 100 nM)-induced basilar artery contraction. The IL-1beta-mediated potentiation was partly suppressed by zinc protoporphyrin (3 microM) and was abolished by tetrodotoxin (TTX, 100 nM), (-)-perillic acid (1 microM), PD98059 (0.3 microM), SB203580 (1 microM) and prazosin (1 microM). Our data suggest that IL-1beta (10 ng/ml) causes an enhancement of U46619-mediated basilar artery contraction that probably involves TTX-sensitive neuronal release of an alpha1-adrenoceptor agonist and activation of p42/p44 and p38 mitogen-activated protein kinases/p21(ras) pathways.

The diacylglycerol lipase inhibitor RHC-80267 potentiates the relaxation to acetylcholine in rat mesenteric artery by anti-cholinesterase action

The diacylglycerol lipase inhibitor 1,6-bis(cyclohexyloximinocarbonylamino) hexane (RHC-80267) was tested for its effect on acetylcholine-evoked relaxation in rat mesenteric artery. In artery contracted with either noradrenaline or KCl, RHC-80267 (0.1-10 muM) potentiated the relaxation evoked by acetylcholine. The effect of RHC-80267 was not affected by nitric oxide synthase inhibition or by inhibitors of protein kinase C or of phospholipase A(2). The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol did not change the relaxation to acetylcholine. RHC-80267 did not affect the relaxation evoked by carbachol, by the nitric oxide donor SNAP (S-nitroso-N-acetylpenicillamine) or by the K(+) channel opener cromakalim. Neostigmine, a cholinesterase inhibitor, produced the same effect as RHC-80267 on acetylcholine-evoked relaxation. When tested on cholinesterase in brain homogenate, RHC-80267 concentration-dependently inhibited cholinesterase activity with an IC(50) of 4 muM. These results indicate that the potentiation of acetylcholine-evoked responses by RHC-80267 in rat mesenteric artery is caused by the inhibition of the cholinesterase activity in the vascular wall.

Contribution of glibenclamide-sensitive, ATP-dependent K+ channel activation to acetophenone analogues-mediated in vitro pulmonary artery relaxation of rat

Compared to the currently available therapeutic drugs for peripheral vascular diseases, agents that are selective for relaxing pulmonary circulation are scarce. The present study was undertaken, using isometric tension change measurement and whole-cell patch-clamp electrophysiology methods, to evaluate the vascular relaxation effect and the underlying mechanisms involved of two naturally found alkaloids: paeonol (2-hydroxy-4-methoxy-acetophenone), acetovanillone (4-hydroxy-3-methoxy-acetophenone) and the non-substituted analogue acetophenone on pulmonary artery of Sprague-Dawley rats. Cumulative administration (3 microM-1 mM) of acetophenone analogues resulted in a concentration-dependent relaxation of phenylephrine (1 microM) pre-contracted pulmonary artery. A relative order of inhibitory potency, estimated by comparing the concentration at which a 50% relaxation of phenylephrine-induced contraction observed was: acetovanillone > paeonol > acetophenone. Endothelial denudation and inhibition of nitric oxide synthase (with 20 microM N(G)-nitro-L-arginine methyl-ester) only moderately suppressed (17.6 +/- 4.2%) acetovanillone- but not paeonol- or acetophenone-mediated maximum relaxation. Glibenclamide (3 microM, an ATP-sensitive K(+) (IK(ATP)) channel blocker) markedly attenuated all acetophenone analogues-mediated endothelium-independent relaxation. Neither cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL 12330A, 10 microM), iberiotoxin (300 nM), 4-aminopyridine (3 mM), (+/-)-propranolol (1 microM, a non-selective beta-adrenoceptor blocker) nor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (3 microM, a guanylate cyclase inhibitor) altered endothelium-independent relaxation. In electrophysiological experiments using single pulmonary artery smooth muscle cells, acetovanillone, paeonol, acetophenone and cromakalim activated glibenclamide-sensitive, IK(ATP) channels. In conclusion, our results demonstrate that acetophenone analogues caused pulmonary artery relaxation through opening of IK(ATP) channels. In addition, acetovanillone-mediated pulmonary artery relaxation is partly depended on nitric oxide released from endothelium.

Muscarinic receptor subtypes mediate vasorelaxation in isolated horse deep dorsal penile vein

OBJECTIVES

To investigate the effect of acetylcholine (ACh) on horse deep dorsal penile vein and to characterize the muscarinic receptor subtypes involved in this response.

METHODS

Vein rings were mounted in an organ bath chamber, and the isometric tension was recorded.

RESULTS

In phenylephrine-contracted veins, ACh (1 nM to 1 microM) induced endothelium-dependent relaxation. The muscarinic receptor antagonist, atropine, produced parallel rightward shifts of the ACh response curves (pA2 = 10.04; pK(B) = 9.98). Carbachol (10 nM to 100 microM) also evoked relaxation in the vein segments, but showed a lower potency and similar relaxation to that induced by ACh. Pirenzepine, the high, intermediate, and low-affinity antagonist for M1, M3, and M2 receptors, respectively, inhibited ACh and carbachol-induced relaxation, yielding pA2 values of 7.51 and 7.37, and pK(B) values of 7.38 and 7.28, respectively. Methoctramine, a high-affinity M2 antagonist, showed no significant effect on the response to ACh. However, a high-affinity M3 antagonist, pFHHSiD, potently blocked the relaxation induced by carbachol and ACh, yielding pA2 and pK(B) values of 7.72 and 7.70 for pFHHSiD against ACh, respectively, and of 7.77 and 7.65 against carbachol, respectively.

CONCLUSIONS

These results indicate that ACh induces an endothelium-dependent relaxation in horse deep dorsal penile vein. The antagonist profile suggests that M3 muscarinic receptors mediate ACh-induced relaxation in this tissue.

An in vitro study of histamine on the pulmonary artery of the Wistar-Kyoto and spontaneously hypertensive rats

The vascular response to most neurotransmitters of different vascular beds is altered under hypertensive condition. The modulatory effect of genetic pulmonary arterial hypertension on histamine responses is not known. The present study was undertaken to evaluate the modulatory effect of enzymatic degradation (via histamine N-methyl-transferase and diamine oxidase) on the vascular response of histamine, and the subtype(s) of histamine receptor present in the pulmonary artery (first branch, O.D. approximately 800 microm) of the normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) (male, 22-26 weeks old). In phenylephrine (1 microM) pre-contracted preparations, histamine and 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl) heptanecarboxamide (HTMT, a histamine H(1) receptor agonist) elicited a concentration-dependent relaxation, with a smaller magnitude recorded in SHR. Application of 10 microM S-[4-(N,N-dimethylamino)-butyl]isothiourea (SKF 91488, a selective histamine N-methyl-transferase inhibitor), but not aminoguanidine (100 microM, a diamine oxidase inhibitor), significantly attenuated histamine-induced relaxation. Clobenpropit (1 nM, a potent histamine H(3) receptor antagonist) "antagonised" the suppressive effect of SKF 91488 and histamine-evoked relaxation was restored. Endothelial denudation reduced histamine- and abolished HTMT-elicited relaxation. Dimaprit (a histamine H(2) receptor agonist) caused an endothelium-independent, cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL 12330A, 10 microM, an adenylate cyclase inhibitor)-sensitive, concentration-dependent relaxation, with a similar magnitude in both strains of rat. Histamine-evoked relaxation was reversed into a further contraction (clobenpropit (10 nM)-sensitive) (with a greater magnitude occurred in the WKY rat) after blocking the histamine H(1) and H(2) receptors with diphenhydramine plus cimetidine (30 microM each). A similar further contraction (clobenpropit-sensitive) was observed with imetit (a histamine H(3)/H(4) receptor agonist) (> or =3 microM). Under resting tension, imetit (> or =0.3 microM) caused a clobenpropit (10 nM)- and prazosin (1 microM)-sensitive, concentration-dependent contraction, with a greater contraction in the WKY rats. Our results suggest that inhibition of histamine catabolism using SKF 91488 (histamine N-methyl-transferase inhibitor) resulted in a reduction of histamine-mediated relaxation that was due to the activation of the clobenpropit-sensitive, histamine H(3)/H(4) receptor and the release of catecholamine. In addition, activation of histamine H(1) and H(2) receptors resulted in relaxation whereas histamine H(3)/H(4) receptor activation by imetit yielded a prazosin-sensitive contraction of the pulmonary artery.

Mechanisms responsible for the in vitro relaxation of ligustrazine on porcine left anterior descending coronary artery

In this study, we have evaluated the underlying mechanisms responsible for the relaxation response of ligustrazine (2,3,5,6-tetra-methyl-pyrazine; 2,3,5,6-MP) and its structural analogues (2-methyl-pyrazine (2-MP); ethyl-pyrazine (EP); 2,3-di-methyl-pyrazine (2,3-MP); 2,5-di-methyl-pyrazine (2,5-MP); 2,6-di-methyl-pyrazine (2,6-MP) and 2,3,5-tri-methyl-pyrazine (2,3,5-MP)) in porcine left anterior descending coronary artery (tertiary branch, O.D. 2,3,5-MP>EP>2,5-MP>/=2,6-MP>/=2,3-MP>2-MP. Besides, salbutamol and forskolin caused an endothelium-independent relaxation. The relaxation response of ligustrazine, salbutamol and forskolin was blunted in the presence of cis-N-(2-phenylcyclopentyl) azacyclotridec-1-en-2-amine (MDL 12330A) (10 microM, an adenylate cyclase inhibitor) and N-[2-((bromocinnamyl)amino)ethyl]-5-isoquinoline-sulphonamide (H-89, a protein kinase A inhibitor, 3 microM). Patch-clamp, whole-cell electrophysiological studies using single smooth muscle cells of the left anterior descending coronary artery revealed that ligustrazine (300 microM), salbutamol (30 microM) and forskolin (1 microM) inhibited the nifedipine-sensitive L-type Ca(2+) channels, and the inhibitory effect was eradicated by MDL 12330A (10 microM) and H-89 (1 microM). However, neither the Ca(2+)-dependent K(+) channel nor the ATP-dependent K(+) channel was modified by ligustrazine (300 microM). In conclusion, our results indicate that ligustrazine-mediated left anterior descending coronary artery relaxation is due to the activation of adenylate cyclase/protein kinase A cascade and the subsequent inhibition of nifedipine-sensitive, voltage-dependent L-type Ca(2+) channels. However, opening of K(+) channels seems to play no role in mediating the relaxation effect of ligustrazine.

Mechanisms for the vasodilations induced by Ginkgo biloba extract and its main constituent, bilobalide, in rat aorta

Vasodilating actions of Ginkgo biloba extract (GBE) and bilobalide, a main constituent, were examined using rat aorta ring strips. GBE at the concentration ranges from 0.03 to 3 mg/ml had a potent concentration-dependent relaxation, reaching 70 +/- 4.5% (n = 6, P < 0.001) at 3 mg/ml. Bilobalide at 0.1 to 100 microM also caused the relaxation in a concentration-dependent manner. At 100 microM, bilobalide caused dilation by 17.6 +/- 3.9% (n = 7, P < 0.05). NG-monomethyl-L-arginine acetate (L-NMMA)(100 microM), an NO synthesis inhibitor, reduced the vasodilation of GBE (3 mg/ml) to 57.6 +/- 2.5% (n = 6, P < 0.05), and was accompanied with a decrease in the rate of relaxation. Tetraethylammonium (TEA)(100 microM), a Ca(2+)-activated K(+) channel inhibitor, also decreased the GBE (3 mg/ml)-induced relaxation to 63.1 +/- 4.6% (n = 6), but not significantly. Indomethacin tended to reduce the GBE (3 mg/ml)-induced vasorelaxation to 67.3 +/- 4.1% (n = 6). In contrast, the vasorelaxation of GBE (3 mg/ml) was strongly attenuated to 53 +/- 6.1% (n = 7, P < 0.05) in Ca(2+)-free medium. Similarly, the vasorelaxation induced by bilobalide significantly decreased both by pretreatment with NO inhibitor (L-NMMA) and in Ca(2+)-free solution. These results indicate that the relaxation induced by GBE would be due to the inhibition of Ca(2+) influx through the Ca(2+) channel and the activation of NO release, and might be in part due to the inhibitions of Ca(2+)-activated K(+) current and PGI(2) release, in the endothelium and aortic vascular muscles. Bilobalide possesses the similar mechanisms for the vasodilation.

Role of Na+/H+ exchanger in acetylcholine-mediated pulmonary artery contraction of spontaneously hypertensive rats

Compared to sympathetic nervous system, the role of parasympathetic innervation on tone development, especially under diseased conditions, of the pulmonary artery is relatively unknown. In this study, the contractile effect of acetylcholine and the type(s) of muscarinic (M) receptor involved in the pulmonary artery (1st intralobar branch; endothelium-denuded, under resting tension) of the normotensive Wistar-Kyoto (WKY) and age-matched (male, 22-26 weeks old) Spontaneously hypertensive rats (SHR) were investigated. Cumulative administration of acetylcholine (> or =0.1 microM) caused a concentration-dependent increase in tension (antagonised by p-fluoro-hexahydro-sila-difenidol and 4-diphenylacetoxy-N-methylpiperidine, both are selective muscarinic M(3) receptor antagonists) and the magnitude of maximum contraction (expressed as % of 50 mM [K(+)](o)-induced contraction) was markedly enhanced in the presence of neostigmine (10 microM, an anti-cholinesterase) (acetylcholine 30 microM, SHR: 72% vs. 35%; WKY: 32% vs. 20%). In SHR only, acetylcholine-elicited contraction was suppressed by 1-[beta-[3-(4-Methoxyphenyl)-propoxyl]-4-methoxyphenethyl]-1H-imidazole (SK&F 96365, 1 microM), amiloride (500 microM), ethyl-isopropyl-amiloride (EIPA, 10 microM), 2-[2-[4-(4-Nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R 7943, 5 microM), 2,4-dichlorobenzamil (10 microM), and an equal molar substitution of [Na(+)](o) (< or =30 mM) with choline or N-methyl-D-glucamine. In nominally [Ca(2+)](o)-free, EGTA (0.5 mM)-containing Krebs' solution, acetylcholine (> or =3 microM) only elicited a small contraction. In conclusion, muscarinic M(3) receptor activation is responsible for the pulmonary artery contraction induced by acetylcholine, with a greater magnitude observed in SHR. The exaggerated contraction in SHR is probably due to an influx of [Na(+)](o) through the Na(+)/H(+) exchanger and the store-operated channels (SOC) into smooth muscle cells. Elevation of cytosolic [Na(+)](i) subsequently leads to an influx of [Ca(2+)](o) through the reverse mode of the Na(+)/Ca(2+) exchanger seems to play a permissive role in mediating the exaggerated contractile response of acetylcholine recorded in the SHR.