European Journal of Pharmacology (v.474, #1)
Editorial Board (IFC).
N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine inhibits ligand binding to certain G protein-coupled receptors by Jack M. Webster; Matthew T. Bentley; Richard J.H. Wojcikiewicz (1-5).
N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) is used widely in biological systems to chelate certain heavy metals, particularly Zn2+. Here we show that TPEN inhibits ligand binding to certain G protein-coupled receptors and is an antagonist at muscarinic receptors. In intact human neuroblastoma SH-SY5Y cells, the binding of the muscarinic receptor ligand [N-methyl-3H]scopolamine methyl chloride was inhibited by TPEN (K i∼26 μM), as was muscarinic receptor agonist-induced inositol 1,4,5-trisphosphate formation (K i∼26 μM). This antagonism was not due to metal ion chelation, indicating that it resulted from a direct interaction of TPEN with muscarinic receptors. Examination of the effects of TPEN on other receptors in SH-SY5Y cell membrane preparations showed that the binding of the nonpeptide opioid receptor ligand [15,16-3H]diprenorphine was strongly inhibited, whereas binding of [125I]vasoactive intestinal polypeptide was not. This pattern of selectivity was also seen in AR4-2J rat pancreatoma cell membranes, in which TPEN inhibited ligand binding to muscarinic receptors, but not that to cholecystokinin receptors. In conclusion, these data show that TPEN inhibits ligand binding to certain G protein-coupled receptors and exhibits selectivity towards those receptors whose transmembrane helices form the predominant site for ligand interaction. TPEN may have widespread antagonistic activity towards G protein-coupled receptors of this kind.
Keywords: TPEN; Ligand binding; G protein-coupled receptor;
Protein kinase A-dependent coupling of mouse prostacyclin receptors to Gi is cell-type dependent by Kevin B.S. Chow; Robert L. Jones; Helen Wise (7-13).
The ability of the prostacyclin (IP) receptor agonist cicaprost to activate Gs-, Gq/11- and Gi-mediated cell signalling pathways has been examined in Chinese hamster ovary (CHO) cells and human embryonic kidney 293 (HEK 293) cells expressing the cloned human (hIP) or mouse (mIP) prostacyclin receptor, and compared with data from NG108-15 and SK-N-SH cells that endogenously express rat/mouse and human IP receptors, respectively. Cicaprost stimulated [3H]cyclic AMP production with EC50 values of 1.5–22 nM, and stimulated [3H]inositol phosphate production (EC50 values 49–457 nM) in all but the SK-N-SH cells. Cicaprost failed to inhibit forskolin-stimulated [3H]cyclic AMP production in any of these cell lines. Therefore, although both human and mouse IP receptors couple to Gs and Gq/11-mediated signalling pathways in a cell type-dependent manner, we could find no evidence for IP receptor coupling to Gi.
Keywords: Prostacyclin receptor; Adenylyl cyclase; Phospholipase C; G protein coupling; Receptor switching;
The opposing effects of endothelin-1 and C-type natriuretic peptide on apoptosis of neonatal rat cardiac myocytes by Bo Han; Ruhama Fixler; Ronen Beeri; Yongchun Wang; Uriel Bachrach; Yonathan Hasin (15-20).
C-type natriuretic peptide (CNP) and endothelin-1 are paracrine peptides with opposing effects on cardiac myocyte contraction and intracellular cGMP production. Elevated levels of both endothelin-1 and CNP are found in patients with congestive heart failure. These factors may be related to positive and negative regulation of cell apoptosis in the failing heart. To evaluate the effect of CNP and endothelin-1 on apoptosis of cardiac myocytes and the possible mechanisms involved, primary cardiac myocytes were prepared from neonatal Sabra rats. Cardiomyocyte apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Annexin V in situ staining. The TUNEL method was used to measure the apoptotic index. CNP and the cGMP derivative, 8-br-cGMP, induced apoptosis of cardiac myocytes. CNP-induced apoptosis could be blocked by HS 142-1 (a mixture of 20–30 kinds of linear β-1, 6-glucan esterified by capronic acid, an antagonist of type A and B natriuretic peptide receptors), and KT 5823 (C29H25N3O5, the inhibitor of cGMP-dependent protein kinase). α-Difluoromethylornithine (DFMO), the irreversible inhibitor of ornithine decarboxylase, also induced apoptosis to a similar extent. CNP and 8-br-cGMP caused a marked reduction of intracellular ornithine decarboxylase expression, as determined by Western blot analysis and immunohistochemical assay. Preincubation with endothelin-1 attenuated CNP- and 8-br-cGMP-induced cardiomyocyte apoptosis. Endothelin-1 also antagonized the CNP- and 8-br-cGMP-induced reduction of intracellular ornithine decarboxylase expression. These results suggest that CNP has a proapoptotic effect on neonatal rat cardiac myocytes. The effect is mediated via natriuretic peptide receptors and is due to an elevation of intracellular cGMP, which reduces the expression of intracellular ornithine decarboxylase and probably the production of polyamines. Endothelin-1 protects cardiac myocytes against CNP-induced apoptosis by influencing the cGMP-dependent pathway, and this effect is probably mediated through both a reduction of cGMP and antagonism of the CNP-induced reduction of intracellular ornithine decarboxylase expression.
Keywords: Apoptosis; Natriuretic peptide; Endothelin; Cardiac myocyte; Ornithine decarboxylase;
Nonpeptide gastrin releasing peptide receptor antagonists inhibit the proliferation of lung cancer cells by Terry W Moody; Julius Leyton; Luis Garcia-Marin; Robert T Jensen (21-29).
The ability of nonpeptide antagonists to interact with gastrin releasing peptide receptors on lung cancer cells was investigated. PD176252 (3-(1H-Indol-3-yl)-N-[1-(5-methoxy-pyridin-2-yl)-cyclohexylmethyl]-2-methyl-2-[3-(4-nitro-phenyl)-ureido]-propionamide) and PD168368 (3-(1H-Indol-3-yl)-2-methyl-2-[3(4-nitro-phenyl)-ureido]-N-(1-pyridin-2-yl-cyclohexylmethyl)-propionamide) inhibited specific 125I-gastrin releasing peptide binding to NCI-H1299 cells with IC50 values of 20 and 1500 nM, respectively. Similar binding results were obtained using NCI-H157, H345 and N592 human lung cancer cells. PD176252 inhibited the ability of 1 nM bombesin to cause elevation of cytosolic calcium in Fura-2 loaded NCI-H345 or H1299 cells, whereas it had no effect on basal cytosolic calcium. PD176252 antagonized the ability of 10 nM bombesin to cause elevation of c-fos mRNA in NCI-H1299 cells. Also, PD176252 inhibited the ability of 100 nM bombesin to cause tyrosine phosphorylation of focal adhesion kinase in NCI-H1299 cells. Using a [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay, PD176252 was more potent than PD168368 at inhibiting NCI-H1299 proliferation. Also, 1 μM PD176252 significantly inhibited lung cancer colony number in vitro. PD176252 in a dose-dependent manner inhibited NCI-H1299 xenograft growth in nude mice in vivo. These results indicate that PD176252 is a gastrin releasing peptide receptor antagonist, which inhibits the proliferation of lung cancer cells.
Keywords: PD176252; Gastrin releasing peptide receptor; Antagonist; Lung cancer; Proliferation;
Ligand internalization by cloned neuropeptide Y Y5 receptors excludes Y2 and Y4 receptor-selective peptides by Steven L. Parker; Michael S. Parker; Armin Buschauer; Ambikaipakan Balasubramaniam (31-42).
In human embryonic kidney-293 (HEK-293) cells, the cloned human neuropeptide Y Y5 receptor saturably internalized agonists, with the rank order of neuropeptide Y-(19-23)-[Gly1,Ser3,Gln4,Thr6,Ala31,Aib32,Gln34]human pancreatic polypeptide (neuropeptide Y-Aib-pancreatic polypeptide)>human neuropeptide Y>porcine peptide YY>[Pro34]human peptide YY>[Leu31,Pro34]human peptide YY≫human peptide YY-(3-36). Human pancreatic polypeptide competed [125I]neuropeptide Y binding and internalization in neuropeptide Y Y5 receptor-expressing cells, but itself showed no internalization. The internalization was strongly dependent on temperature. The surface binding, and especially the internalization, of human neuropeptide Y were highly sensitive to the clathrin network inhibitor phenylarsine oxide, and to the cholesterol-complexing antibiotic filipin III. The internalized ligands were present in particles corresponding to secondary endosomes in Percoll gradients, but especially in particles banding with the acid hexosaminidase lysosomal marker. At any temperature tested, internalization of the neuropeptide Y Y5 receptor driven by human neuropeptide Y in HEK-293 cells was much slower than the internalization of the neuropeptide Y Y1 receptor reported in the same cells, or in Chinese hamster ovary (CHO) cells. The neuropeptide Y Y5 receptor subtype could be the metabotropic receptor responding to protracted challenges by neuropeptide Y-like peptides, and its density could be little sensitive to concentration of extracellular agonists.
Keywords: Receptor conservation; Receptor affinity; Endocytosis rate; Lysosomal sorting; Endosomal sorting; Selective agonist endocytosis; Buoyant density separation;
Functional expression of adenosine A2A and A3 receptors in the mouse dendritic cell line XS-106 by John M. Dickenson; Steve Reeder; Bob Rees; Steve Alexander; Dave Kendall (43-51).
There is increasing evidence to suggest that adenosine receptors can modulate the function of cells involved in the immune system. For example, human dendritic cells derived from blood monocytes have recently been described to express functional adenosine A1, A2A and A3 receptors. Therefore, in the present study, we have investigated whether the recently established murine dendritic cell line XS-106 expresses functional adenosine receptors. The selective adenosine A3 receptor agonist 1-[2-chloro-6[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-β-d-ribofuranuronamide (2-Cl-IB-MECA) inhibited forskolin-mediated [3H]cyclic AMP accumulation and stimulated concentration-dependent increases in p42/p44 mitogen-activated protein kinase (MAPK) phosphorylation. The selective adenosine A2A receptor agonist 4-[2-[[-6-amino-9-(N-ethyl-β-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzene-propanoic acid (CGS 21680) stimulated a robust increase in [3H]cyclic AMP accumulation and p42/p44 MAPK phosphorylation. In contrast, the selective adenosine A1 receptor agonist CPA (N 6-cyclopentyladenosine) did not inhibit forskolin-mediated [3H]cyclic AMP accumulation or stimulate increases in p42/p44 MAPK phosphorylation. These observations suggest that XS-106 cells express functional adenosine A2A and A3 receptors. The non-selective adenosine receptor agonist 5′-N-ethylcarboxamidoadenosine (NECA) inhibited lipopolysaccharide-induced tumour necrosis factor-α (TNF-α) release from XS-106 cells in a concentration-dependent fashion. Furthermore, treatment with Cl-IB-MECA (1 μM) or CGS 21680 (1 μM) alone produced a partial inhibition of lipopolysaccharide-induced TNF-α release (when compared to NECA), whereas a combination of both agonists resulted in the inhibition of TNF-α release comparable to that observed with NECA alone. Treatment of cells with the adenosine A2A receptor selective antagonists 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5ylamino]ethyl)phenol (ZM 241385; 100 nM) and 5-amino-2-(2-furyl)-7-phenylethyl-pyrazolo[4,3-e]-1,2,4-triazolo[1,5c]pyrimidine (SCH 58261; 100 nM) and the adenosine A3 receptor selective antagonist N-[9-chloro-2-(2-furanyl)[1,2,4]-triazolo[1,5-c]quinazolin-5-benzeneacetamide (MRS 1220; 100 nM) partially blocked the inhibitory effects of NECA on lipopolysaccharide-induced TNF-α release. Combined addition of MRS 1220 and SCH 58261 completely blocked the inhibitory effects of NECA on lipopolysaccharide-induced TNF-α release. In conclusion, we have shown that the mouse dendritic cell line XS-106 expresses functional adenosine A2A and A3 receptors, which are capable of modulating TNF-α release.
Keywords: Adenosine A3 receptor; Adenosine A2A receptor; Dendritic cell; TNF-α (tumour necrosis factor-α);
In vivo neuroprotective effects of ACEA 1021 confirmed by magnetic resonance imaging in ischemic stroke by Margaret A Petty; Claudia Neumann-Haefelin; Juergen Kalisch; Shakir Sarhan; Joseph G Wettstein; Hans-Paul Juretschke (53-62).
The neuroprotective activity of ACEA 1021 (5-nitro-6,7-dichloro-1,4-dihydro-2,3-quinoxalinedione; licostinel), a selective antagonist at the strychnine-insensitive glycine site associated with the NMDA receptor complex, has been investigated in various models of focal cerebral ischemia. In isoflurane-anaesthesised Wistar rats with permanent ipsilateral carotid artery ligation and transient middle cerebral artery occlusion (duration of occlusion, 2 h) followed by reperfusion (24 h), intravenous administration of ACEA 1021 (bolus: 10 mg/kg, 15 min after the onset of middle cerebral artery occlusion; infusion: 7 mg/kg/h for 6 h beginning 30 min after occlusion of the artery) produced a 32% reduction in infarct volume. Similarly, in Sprague–Dawley rats with transient middle cerebral artery occlusion (2 h) followed by 24 h of reperfusion, identical treatment with ACEA 1021 decreased infarct size by 39%. Magnetic resonance imaging (MRI) confirmed these effects in the transient model, in that infarct volume observed using apparent diffusion coefficient (ADC) maps was significantly smaller after 24 h in the ACEA 1021-treated rats compared with Tris-treated controls. Furthermore, the increase in perfusion signal intensity after reperfusion was more pronounced in the ACEA 1021-treated rats than in controls. In Fisher 344 rats with permanent occlusion of the middle cerebral artery, ACEA 1021 induced a dose-related decrease in infarct volume, which was associated with an improvement in neurological outcome as measured by the rope suspension procedure. Administration of the same dose regimen, as above, in Fisher rats with permanent middle cerebral artery occlusion reduced infarct volume by 68%. This dose was as effective when administration was delayed for 2 h. In mice with permanent middle cerebral artery occlusion, ACEA 1021 (5 mg/kg, i.v., 5 min after occlusion; 30 mg/kg, s.c., 1 and 4 h post-middle cerebral artery occlusion) decreased infarct size by 42%. The consistent anti-ischemic effects of ACEA 1021 make it a valuable compound for exploratory stroke research.
Keywords: Middle cerebral artery occlusion; Ischemia; Reperfusion; Body temperature; Neurological deficit; Diffusion–perfusion magnetic resonance imaging;
Behavioral sensitization and alteration in monoamine metabolism in mice after single versus repeated methamphetamine administration by Nobue Kitanaka; Junichi Kitanaka; Motohiko Takemura (63-70).
To address the functional alterations of monoaminergic neuronal systems in mice after single and repeated administration of methamphetamine, we examined the tissue contents of monoamines and their metabolites in addition to locomotor activity estimated by horizontal locomotion and rearing measurements. In male ICR mice, the repeated treatment regimen (intraperitoneal administration of 1.0 mg/kg methamphetamine once per day for five consecutive days) induced hyperlocomotion with a plateau level on test day 4. The initial behavioral response (within 5 min after injection) to the drug appeared to include context-dependent sensitization. Mice after the initial repeated treatment regimen showed behavioral sensitization to the same dose of methamphetamine 5 days after the final injection (test day 11). On test day 11, the first 150 min, but not the nocturnal behavior (during the dark hours), were significantly enhanced after the drug challenge. A marked reduction of the content of l-dihydroxyphenylalanine and the ratio of 3,4-dihydroxyphenylacetic acid to dopamine was observed in the striatum+accumbens of mice after single and repeated administration of methamphetamine. As for serotonin metabolism, the ratio of 5-hydroxyindolacetic acid to serotonin significantly increased in mice after single administration of methamphetamine, although it decreased in mice after repeated administration of methamphetamine. Norepinephrine metabolism (the ratio of 3-methoxy-4-hydroxyphenylglycol to norepinephrine) was not affected in the striatum+accumbens or thalamus+hypothalamus of the mice after repeated or single methamphetamine treatment. These results suggest that dopaminergic and serotonergic neuronal activities were altered during the development of behavioral sensitization. The ratio of 3-methoxytyramine to dopamine was not affected, suggesting that the methamphetamine treatment selectively inhibited the monoamine oxidase pathway for dopamine inactivation.
Keywords: Methamphetamine; Behavioral sensitization; Nocturnal behavior; Monoamine metabolism; Dopamine; 5-HT (5-hydroxytryptamine; serotonin);
Subsensitivity of P2X but not vanilloid 1 receptors in dorsal root ganglia of rats caused by cyclophosphamide cystitis by Sebestyen J. Borvendeg; Mahmoud Al-Khrasani; Patrizia Rubini; Wolfgang Fischer; Clemens Allgaier; Kerstin Wirkner; Herbert M. Himmel; Clemens Gillen; Peter Illes (71-75).
The application of cyclophosphamide to rats was used to induce interstitial cystitis. Behavioural studies indicated a strong pain reaction that developed within 2 h and levelled off thereafter causing a constant pain during the following 18 h. Neurons prepared from L6/S1 dorsal root ganglia innervating the urinary bladder responded to the application of capsaicin or α,β-methylene ATP (α,β-meATP) with an increase of intracellular Ca2+ ([Ca2+] i ). The [Ca2+] i responses to capsaicin were identical in the dorsal root ganglion cells of cyclophosphamide- and saline-treated rats, whereas α,β-meATP induced less increase in [Ca2+] i in the cyclophosphamide-treated animals than in their saline-treated counterparts. Hence, α,β-meATP-sensitive P2X3 and/or P2X2/3 receptors of L6/S1 dorsal root ganglion neurons were functionally downregulated during subacute pain caused by experimental cystitis. In contrast, capsaicin-sensitive vanilloid 1 receptors did not react to the same procedure. Thoracal dorsal root ganglia, not innervating the urinary bladder, were also unaltered in their responsiveness to α,β-meATP by cyclophosphamide treatment.
Keywords: Dorsal root ganglion; P2X receptor; Vanilloid 1 receptor; Cyclophosphamide-induced cystitis;
Behavioral evidence for μ-opioid and 5-HT2A receptor interactions by Gerard J. Marek (77-83).
Electrophysiological studies have demonstrated a physiological interaction between 5-HT2A and μ-opioid receptors in the medial prefrontal cortex. Furthermore, behavioral studies have found that phenethylamine hallucinogens induce head shakes when directly administered into the medial prefrontal cortex. The receptor(s) by which morphine suppresses head shakes induced by serotonin agonists have not been characterized. We administered μ-opioid receptor agonists and antagonists to adult male Sprague–Dawley rats prior to treatment with the phenethylamine hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), which is known to induce head shakes via 5-HT2A receptors. The suppressant action of the moderately selective μ-opioid receptor agonist, buprenorphine (ID50∼0.005 mg/kg, i.p.; a μ-opioid receptor partial agonist and κ-opioid receptor antagonist) was blocked by naloxone and pretreatment with the irreversible μ-opioid receptor antagonist clocinnamox. Another μ-opioid receptor agonist fentanyl also suppressed DOI-induced head shakes. In contrast, a δ-opioid receptor agonist was without effect on DOI-induced head shakes. Thus, activation of μ-opioid receptors can suppress head shakes induced by hallucinogenic drugs.
Keywords: Phenethylamine; Hallucinogen; 5-HT (5-hydroxytryptamine, serotonin); μ-Opioid receptor; Head shake; DOI; 5-HT2A receptor; Buprenorphine; Fentanyl;
Behavioral and biochemical investigations of bupropion metabolites by Mikhail L Bondarev; Tatiana S Bondareva; Richard Young; Richard A Glennon (85-93).
The stimulus effects of bupropion metabolites were examined in a drug discrimination procedure using (−)nicotine- and (+)amphetamine-trained rats. (+)- and (−)threohydrobupropion partially substituted in each group. R,R-hydroxybupropion produced vehicle-appropriate responding in (−)nicotine animals but, when given in combination with the training dose of (−)nicotine, resulted in an attenuated effect. S,S-Hydroxybupropion partially (66%) substituted for (−)nicotine. In (+)amphetamine-trained animals, S,S-hydroxybupropion (ED50=4.4 mg/kg) generalized completely and was similar in potency to bupropion (ED50=5.4 mg/kg). Bupropion and its metabolites lacked affinity for nicotinic acetylcholinergic receptors, but all antagonized (−)nicotine-induced 86Rb+ efflux in cells expressing α3β4 nicotinic cholinergic receptors. S,S-Hydroxybupropion possessed affinity at the dopamine transporter comparable to bupropion, and was also found to bind at the norepinephrine transporter. Although it is unlikely that any metabolite isomer is chiefly responsible for the stimulus actions of bupropion, some probably play a role in the complex actions of this agent.
Keywords: Nicotine; Amphetamine; Bupropion; Bupropion metabolite; Hydroxybupropion; Threohydrobupropion;
Involvement of the melanocortin MC4 receptor in stress-related behavior in rodents by Shigeyuki Chaki; Shin-ichi Ogawa; Yoshihisa Toda; Takeo Funakoshi; Shigeru Okuyama (95-101).
The melanocortin subtype 4 (MC4) receptor has been postulated to be involved in stress and stress-related behavior. We made use of melanocortin MC4 receptor agonists and antagonist to investigate the relationship between the melanocortin MC4 receptor and stress related disorders. The nonspecific melanocortin receptor agonist α-melanocyte stimulating hormone (α-MSH) and the melanocortin MC4 receptor agonist, Ac-[Nle4,Asp5,d-Phe7,Lys10]α-MSH-(4-10)-NH2 (MT II) dose-dependently and significantly reduced the number of licking periods in the rat Vogel conflict test, suggesting that stimulation of the melanocortin MC4 receptor causes anxiogenic-like activity in rats. We synthesized a peptidemimetic melanocortin MC4 receptor selective antagonist, Ac-d-2Nal-Arg-2Nal-NH2 (MCL0020), which has high affinity for the melanocortin MC4 receptor with IC50 values of 11.63±1.48 nM, in contrast, the affinities for melanocortin MC1 and MC3 receptors were negligible. In addition, MCL0020 significantly attenuated the cAMP formation induced by α-MSH in COS-1 cells expressing the melanocortin MC4 receptor without affecting basal cAMP contents. Thus, we considered MCL0020 to be a selective melanocrotin MC4 receptor antagonist among melanocortin receptors. Restraint stress significantly reduced food intake in rats, and i.c.v. administration of MCL0020 dose-dependently and significantly attenuated restraint stress-induced anorexia without affecting food intake. Swim stress induced reduction in the time spent in the light area in the mouse light/dark exploration test, and MCL0020 significantly prevented it. Taken together our findings suggest that the melanocortin MC4 receptor might be related to stress-induced changes in behavior, and blockade of the melanocortin MC4 receptor may prevent stress-induced disorders such as anxiety.
Keywords: Melanocortin MC4 receptor; Melanocortin; Anxiety; MCL0020; MT II (Ac-[Nle4,Asp5,d-Phe7,Lys10]α-MSH-(4-10)-NH2);
Ca2+-activated K+ channels in the endothelial cell layer involved in modulation of neurogenic contractions in rat penile arteries by Attila Kun; Ana Cristina Martinez; László B. Tankó; János Pataricza; Julius Gy. Papp; Ulf Simonsen (103-115).
The present study was designed to investigate the functional K+ channels involved in contractions induced by electrical field stimulation in isolated rat penile arteries. Blockers of Ca2+-activated K+ channels (KCa), tetraethylammonium, and of large-conductance KCa channels, charybdotoxin and iberiotoxin, as well as a blocker of voltage-dependent K+ channels (KV), 4-aminopyridine, increased resting tension in penile small arteries. In the presence of propranolol and N G-nitro-l-arginine (l-NOARG), electrical field stimulation evoked prazosin-sensitive contractions. In endothelium-intact preparations, these latter contractions were enhanced in the presence of tetraethylammonium and charybdotoxin. However, these blockers did not enhance contractions evoked by exogenously added noradrenaline. Endothelial cell removal increased the neurogenic contractions but tetraethylammonium had no further potentiating effect in these preparations. In the presence of an inhibitor of cyclooxygenase, indomethacin, and inhibitor of nitric oxide (NO) synthase, l-NOARG, acetylcholine evoked relaxations, which were abolished in the presence of either tetraethylammonium or charybdotoxin. In phenylephrine-contracted arteries treated with guanethidine and atropine, electrical field stimulation evoked relaxations, which were partially inhibited by l-NOARG and tetraethylammonium, without any additive effect of these drugs. These observations suggest that both large-conductance KCa channels and KV channels sensitive to iberiotoxin/tetraethylammonium and 4-aminopyridine, respectively, are directly involved in the modulation of myogenic tone of rat penile arteries. Furthermore, activation of endothelial intermediate-conductance KCa channels sensitive to tetraethylammonium and charybdotoxin leads to release of a non-NO nonprostanoid factor, which inhibits release of the neurotransmitter, noradrenaline, but these channels do not appear to be involved in inhibition of contraction evoked by exogenously applied noradrenaline in rat penile arteries.
Keywords: Endothelium; Electrical field stimulation; KCa channel; KV channel; KATP channel; Penile small artery;
SL65.0472 blocks 5-hydroxytryptamine-induced vasoconstriction in a dog hindlimb ischemia model by Fabrice Barbe; Etienne Gautier; Jean-Pierre Bidouard; Alain Grosset; Stephen E. O'Connor; Philip Janiak (117-120).
We have studied the ability of SL65.0472 (7-fluoro-2-oxo-4-[2-[4-(thieno[3,2-c]pyridin-4-yl)piperazin-1-yl]ethyl]-1,2-dihydroquinoline-1-acetamide), a 5-hydroxytryptamine (5-HT) 5-HT1B/5-HT2A receptor antagonist, to antagonise the vasoconstrictor effects of 5-HT and sumatriptan in a canine model of hindlimb ischemia. Dogs underwent right external iliac artery ligation and right superficial femoral artery excision, resulting in decreased perfusion (−31%, P<0.05) in the right hindlimb. Following pretreatment with l-NAME, phentolamine and propranolol, intra-aortic injection of 5-HT markedly reduced blood flow to the right ischemic hindlimb (−50±2%, P<0,05). 5-HT induced vasoconstriction was significantly inhibited (−66%, P<0.05) by SL65.0472 (300 μg/kg i.v.), but unaffected by ketanserin (300 μg/kg i.v.), a 5-HT2A receptor antagonist. SL65.0472 also blocked sumatriptan-induced vasoconstriction in ischemic and normally perfused hindlimbs. Thus, SL65.0472 is an effective antagonist of 5-HT-receptor mediated hindlimb vasoconstriction.
Keywords: 5-HT receptor; Sumatriptan; Vasoconstriction; Hindlimb ischemia; SL65.0472; Ketanserin;
Herbimycin A attenuates apoptosis during heat stress in rats by Shankar B. Sachidhanandam; Jia Lu; Kerwin S.Y. Low; Shabbir M. Moochhala (121-128).
Expression of heat shock proteins (HSPs) as a heat stress response is associated with acquisition of thermotolerance. Herbimycin A is a tyrosine kinase inhibitor that has been shown to induce HSPs. The present study aims to investigate the effects of herbimycin A on thermotolerance in rats subjected to heat stress exposure. Herbimycin A induced hsp70 to peak levels 12 h post-injection in rats without heat stress. No change in hsp70 levels was observed in the vehicle- and saline-treated rats. In rats exposed to heat stress at 45 °C for 25 min, 12 h post-treatment, lower peak temperatures were attained in herbimycin A-treated group as compared to the vehicle- and saline-treated groups. Terminal transferase-mediated d-UTP nick end labeling (TUNEL) showed that a significant decrease in apoptosis of hepatocytes in herbimycin A-treated rats as compared to the vehicle- and saline-treated rats. Caspase-3 activation was also lower in herbimycin A-treated rats, compared to the vehicle- and saline-treated rats. The present study has demonstrated that herbimycin A is effective for development of thermotolerance and therefore protects rats from heat stress.
Keywords: Heat shock protein; Herbimycin A; Thermotolerance; Apoptosis; (Rat);
Role of endothelin ETA receptors in sepsis-induced mortality, vascular leakage, and tissue injury in rats by Mariangela Albertini; Maria Giovanna Clement; Sabah N.A. Hussain (129-135).
The role of endothelin ETA receptors in sepsis-induced mortality and edema formation was evaluated with a selective antagonist ABT-627 [2-(4-methoxyphenyl)-4-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)amino carbonylmethyl)-pyrrolidine-3-carboxylic acid]. Sprague–Dawley rats received saline (control group), Escherichia coli endotoxin (10 mg/kg, sepsis group) or infusion of ABT-627 prior and immediately after saline and endotoxin injection. Mortality, edema formation (wet/dry ratios), and multiple tissue injury (indicated by serum concentrations of creatinine, urea, bilirubin, creatine kinase, lactate dehydrogenase, and aspartate aminotransferase) were monitored within 5 h. Endotoxin injection elicited 64% mortality, significantly augmented edema formation in liver, heart, lung, and kidney, and raised serum levels of tissue injury markers. Pretreatment with ABT-627 completely reversed endotoxin-induced mortality, significantly attenuated wet/dry ratios of the heart, liver, and kidney, but not lungs, and reduced serum levels of creatine kinase, creatinine, aspartate aminotransferase, and lactate dehydrogenase, but not that of urea and bilirubin. These results suggest that endothelin ETA receptors play a significant role in promoting mortality, edema formation (except in the lungs), and tissue injury in animals with severe sepsis.
Keywords: Sepsis; Septic shock; Endothelin; Endothelin receptor; Cardiac output; Organ failure; Edema;