bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localization and activity of haem oxygenase and functional effects of carbon monoxide in the feline lower oesophageal sphincter
Authors: Ny Lars , Alm Per , Ekström Peter , Larsson Bengt , Grundemar Lars , Andersson Karl‐Erik 
Published: July 2012

In the feline lower oesophageal sphincter (LOS), the distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)−‐1 and −2 was studied by immunohistochemistry and confocal microscopy, the HO activity was measured and the possible role for CO as a mediator of relaxation was investigated.
HO‐2 immunoreactivity was abundant in nerve cell bodies of the submucosal and myenteric plexus. Approximately 50% of the HO‐2‐containing myenteric cell bodies were also nitric oxide synthase‐ and vasoactive intestinal peptide (VIP)‐immunoreactive. In addition, HO‐2 immunoreactivity was seen in nerve fibres, in non‐neuronal cells dispersed in the smooth muscle and in arterial endothelium. HO‐1 immunoreactivity was confined to non‐neuronal cells in the smooth muscle, similar to those positive for HO‐2.
Activity of HO, measured as CO production, was observed in LOS homogenates at a rate of 1.00±0.05 nmol mg−1 protein h−1. This production was inhibited by the HO inhibitor, zinc protoporphyrin‐IX (ZnPP).
In isolated circular smooth muscle strips of LOS, developing spontaneous tone, exogenously administered CO evoked a concentration‐dependent relaxation reaching a maximum of 93±3%. This relaxation was accompanied by an increase in cyclic GMP, but not cyclic AMP levels. The relaxant response was attenuated by methylene blue, but unaffected by tetrodotoxin. Repeated exposure to CO resulted in a progressive reduction of the relaxant response.
ZnPP caused a rightward‐shift of the concentration‐response curves for the relaxant responses to VIP, peptide histidine isoleucine, and pituitary adenylate cyclase activating peptide 27.
ZnPP and tin protoporphyrin‐IX (another inhibitor of HO) did not affect nonadrenergic, noncholinergic relaxations induced by electrical field stimulation. Nor did ZnPP affect relaxations induced by 3‐morpholino‐sydnonimine or forskolin.
The present findings, showing localization of HO immunoreactivity to both neuronal and non‐neuronal cells of the feline LOS, ability of LOS to produce CO and a relaxant effect of CO in circular LOS muscle, suggest a role for CO as a peripheral messenger.
Inhibition of neuromuscular transmission in the myenteric plexus of guinea‐pig ileum by ω‐conotoxins GVIA, MVIIA, MVIIC and SVIB
Authors: Hong S.J. , Roan Yow‐Fen , Chang C.C. 
Published: July 2012

The effects of a number of Ca2+ channel blockers on the transmural electrical stimulation or receptor agonist‐elicited contractile responses of guinea‐pig ileum were compared.
ω‐Conotoxins (MVIIA, GVIA, SVIB and MVIIC), but not ω‐agatoxin IVA, completely blocked the twitch responses evoked by low frequency (0.1 Hz) transmural stimulation without inhibition of the contractures evoked by exogenous acetylcholine. The concentration‐inhibition curves were shifted by changes of external Ca2+.
The tetanic contractures produced by a high frequency (30 Hz) train of stimulation were inhibited by ω‐conotoxins by only 25–30%, except for ω‐conotoxin MVIIC, which produced about 55% inhibition, all significantly less than that produced by atropine (about 70%) or tetrodotoxin (about 85%). Combinations of ω‐conotoxins did not produce additive inhibitory effects.
The four ω‐conotoxins as well as atropine produced similar partial inhibition (53–62%) of the contractures evoked by dimethylphenylpiperazinium, while tetrodotoxin inhibited the contracture completely.
Nifedipine and Ni2+ depressed the nerve stimulation‐evoked twitch response and tetanic contracture as well as acetylcholine contracture.
These observations suggest that, in the myenteric plexus, a subset of N‐type Ca2+ channel dominates under low frequency stimulation, while high frequency stimulation may recruit additional channels and non‐cholinergic pathways.
The relaxant 5‐HT receptor in the dog coronary artery smooth muscle: pharmacological resemblance to the cloned 5‐ht7 receptor subtype
Authors: Terrón José A. 
Published: July 2012

The relaxant effect of 5‐hydroxytryptamine (5‐HT) in the dog isolated coronary artery deprived of endothelium is mediated by a receptor unrelated to the 5‐HT1, 5‐HT2, 5‐HT3 or 5‐HT4 types. Based upon the pharmacological characteristics of this relaxant 5‐HT receptor and those reported for the new members of the 5‐HT receptor family, the present study explored the possibility that the relaxant 5‐HT receptor referred to above, corresponds to the cloned 5‐ht7 subtype. Thus, the relaxing and/or blocking effects of several 5‐HT receptor drugs as well as some typical and atypical antipsychotic drugs with high affinity for the cloned 5‐ht7 receptor in precontracted ring segments were analyzed.
5‐HT, 5‐carboxamidotryptamine (5‐CT) and 5‐methoxytryptamine, but not 8‐OH‐DPAT or sumatriptan, produced concentration‐dependent relaxations in endothelium‐denuded canine coronary artery rings precontracted with prostaglandin F2α (2 μm). Clozapine (1 μm) produced in some cases a small relaxing effect and antagonized 5‐HT‐ and 5‐CT‐induced relaxation suggesting a partial agonist effect. In the presence of the 5‐HT1D receptor antagonist, GR127935 (100 nM), the rank order of agonist potency was 5‐CT > 5‐HT > clozapine ≥ 5‐methoxytryptamine. 8‐OH‐DPAT and sumatriptan remained inactive as agonists.
In GR 127935‐treated preparations, methiothepin (3 nM) and mianserin (1 μm), as well as the antipsychotics, clozapine (1 μm), pimozide (300 nM), risperidone (3 nM) and spiperone (1 μm), failed to induce a significant relaxation in prostaglandin F2α‐precontracted vessels, but produced significant rightward displacements of the concentration‐response curves to 5‐HT and 5‐CT without significantly reducing the Emax. In a final set of experiments with 5‐CT, metergoline (100 nM) and mesulergine (300 nM) behaved as competitive antagonists. In contrast, lisuride (3 nM) noncompetitively antagonized 5‐CT‐induced relaxation. The estimated affinity (apparent pKB values) of the above antagonist drugs for the relaxant 5‐HT receptor significantly correlated with their reported affinity at the cloned 5‐ht7 receptor.
Taken together, the above pharmacological data may suggest that the relaxant 5‐HT receptor in the smooth muscle of the canine coronary artery is similar to the cloned 5‐ht7 receptor subtype.
Cyclic AMP‐dependent regulation of K+ transport in the rat distal colon
Authors: Diener M. , Hug F. , Strabel D. , Scharrer E. 
Published: July 2012

The effect of agonists of the cyclic AMP pathway and of 293B, a chromanole‐derived K+ channel blocker, on K+ transport in the rat distal colon was studied by measuring unidirectional fluxes, uptake, and efflux of Rb+ in mucosa‐submucosa preparations and by patch‐clamp of crypt epithelia from isolated crypts.
293B concentration‐dependently inhibited basal and forskolin‐stimulated short‐circuit current. In isolated crypts 293B blocked a basal K+ conductance but had no effect on cyclic AMP‐evoked depolarization induced by the opening of apical Cl− channels. When the effect of cyclic AMP on Cl− conductance was prevented by substituting Cl− with gluconate, an inhibition of total cellular K+ conductance by forskolin and a membrane‐permeable cyclic AMP analogue was unmasked.
Unidirectional ion flux measurements revealed that 293B suppressed the increase in JRbsm induced by forskolin. This, together with the inhibition of cyclic AMP‐induced anion secretion indicates that the drug blocks K+ channels, presumably both in the apical and the basolateral membrane. Forskolin caused not only inhibition of K+ absorption, but also stimulation of K+ secretion. The inhibition was diminished, but not blocked, in the presence of inhibitors of the apical H+‐K+‐ATPase, vanadate and ouabain. Forskolin stimulated serosal, bumetanide‐sensitive Rb+ uptake, whereas mucosal, ouabain/vanadate‐sensitive uptake remained unaffected.
Efflux experiments revealed that forskolin caused a redistribution of cellular K+ efflux reducing the ratio of basolateral versus apical Rb+ efflux.
These results suggest that intracellular cyclic AMP exerts its effects on K+ transport by several mechanisms: an increase in the driving force for K+ efflux due to the depolarization induced by opening of Cl− channels, a stimulation of the basolateral uptake of K+ via the Na+‐K+‐Cl−‐cotransporter, and a decrease of the ratio of basolateral versus apical K+ conductance leading to an enhanced efflux of K+ into the lumen and a reduced K+ efflux to the serosal compartment.
Contribution of calcium‐activated potassium channels to the vasodilator effect of bradykinin in the isolated, perfused kidney of the rat
Authors: Rapacon M. , Mieyal P. , McGiff J.C. , Fulton D. , Quilley J. 
Published: July 2012

NO‐ and prostaglandin‐independent, endothelium‐dependent vasodilator responses to bradykinin are attributed to release of a hyperpolarizing factor. Therefore, the contribution of K+ channels to the renal vasodilator effect of bradykinin was examined in rat perfused kidneys that were preconstricted with phenylephrine and treated with NG‐nitro‐L‐arginine (L‐NOARG) and indomethacin to inhibit NO and prostaglandin synthesis.
The non‐specific K+ channel inhibitors, TEA and TBA reduced vasodilator responses to bradykinin and cromakalim but not those to nitroprusside.
Glibenclamide, an inhibitor of ATP‐sensitive K+ channels, blocked the vasodilator response to cromakalim without affecting responses to bradykinin.
Charybdotoxin, a selective inhibitor of Ca2+‐activated K+ channels, greatly attenuated vasodilator responses to bradykinin without affecting those to cromakalim or nitroprusside.
Iberiotoxin and leiurotoxin, inhibitors of large and small conductance Ca2+‐activated K+ channels, respectively, were without effect on vasodilator responses to bradykinin, cromakalim or nitroprusside.
These results implicate K+ channels, specifically Ca2+‐activated K+ channels of intermediate conductance, in the renal vasodilator effect of bradykinin and, thereby, support a role for a hyperpolarizing factor.
Potentiation of purinergic transmission by angiotensin in prostatic rat vas deferens
Authors: Sum Chi‐Shing , Wan David C.C. , Cheung Wing‐Tai 
Published: July 2012

Angiotensin II (AII) elicited only a minute, if any, direct contractile response in smooth muscle cells of prostatic rat vas deferens, but it potentiated contractile responses to field stimulation.
Angiotensin‐potentiated contractile response to field stimulation was concentration‐dependent, and the order of potency was AII > AIII ≅ AI. The EC50 of AII was 8.11 ± 2.79 nM.
AII did not modify the contractile response of exogenous noradrenaline (NA) on non‐stimulated prostatic vas deferens. Furthermore, the concentration‐response curve for AII‐potentiated contractile responses to field stimulation in reserpine‐treated rats did not significantly differ from the control group.
Desensitization of purinoceptors with 30 μm α, β‐methylene‐ATP almost completely abolished the potentiation of the contractile response to field stimulation by AII.
The response to AII in the prostatic rat vas deferens was blocked by the AT1 selective antagonist losartan, but not by the AT2 selective antagonist CGP 42112. Losartan acted as a competitive antagonist with a pA2 value of 8.75.
In conclusion, AII potentiated purinergic transmission in the prostatic rat vas deferens via the AT1 receptor.
Pharmacological characterization of metabotropic glutamate receptors potentiating NMDA responses in mouse cortical wedge preparations
Authors: Mannaioni Guido , Carlà Vincenzo , Moroni Flavio 
Published: July 2012

Mouse cortical wedge preparations were used in order to study the effects of metabotropic glutamate receptor (mGluR) agonists and antagonists on the depolarization induced by N‐methyl‐D‐aspartate (NMDA) or by (S)‐α‐amino‐4‐bromo‐3‐hydroxy‐5‐isoxazolepropionic acid (AMPA).
(1S, 3R)‐1‐aminocyclopentane‐1, 3‐dicarboxylic acid (1S, 3R‐ACPD) (30–300 μm) significantly potentiated the depolarizations induced by NMDA, leaving unchanged those mediated by AMPA. This potentiation developed slowly and lasted for up to 60 min provided that the slices were continuously perfused with the mGluR agonist.
Concentration‐response curves to NMDA in the absence and in the presence of 1S, 3R‐ACPD (100 μm) indicated that the potentiation was due to increased affinity of the NMDA receptor complex for its agonist. The maximal responses to NMDA were not potentiated.
Selective agonists of group 1 mGluR such as quisqualate (Quis) (30 μm) or (RS)‐3, 5‐dihydroxyphenylglycine (DHPG) (300 μm) did not potentiate NMDA responses. Similarly, selective agonists of group 2 mGluRs, such as (2S, 3S, 4S)‐α‐carboxycyclopropyl‐glycine (L‐CCG‐I) (3–30 μm), and of group 3, such as L‐2‐amino‐4‐phosphonobutyric acid (L‐AP4) (100 μm) were inactive in our test. A number of other putative mGluR agents having partial agonist activity on mGluRs in brain slices and in expression systems, such as 1R, 3S‐ACPD (500 μm), DL‐2‐amino‐3‐phosphonopropionic acid (DL‐AP3) (300 μm) and (S)‐4‐carboxy‐3‐hydroxyphenylglycine (S‐4C3HPG; 500 μm), when placed in the experimental protocol we used, did not change NMDA responses.
Available mGluR antagonists, such as DL‐AP3 (1 mM), (+)‐α‐methyl‐4‐carboxyphenylglycine (MCPG) (500 μm), S‐4‐carboxyphenylglycine (4CPG; 500 μm) and S‐4‐carboxy‐3‐hydroxyphenylglycine (S‐4C3HPG; 500 μm), did not reduce 1S, 3R‐ACPD potentiation of NMDA responses.
It is concluded that the potentiation of NMDA currents induced by the mGluR agonist 1S, 3R‐ACPD, in mouse cortical wedges, has a pharmacological profile which is different from that of the three mGluR groups so far described in expression systems.
The contribution of nitric oxide to endotoxin‐induced ocular inflammation: interaction with sensory nerve fibres
Authors: Wang Zun‐Yi , Alm Per , Håkanson Rolf 
Published: July 2012

The actions of nitric oxide (NO) have been investigated in an endotoxin‐evoked ocular inflammatory model in the rabbit, with particular emphasis on the relationship between NO, sensory nerves (C‐fibres) and the C‐fibre neuropeptides, calcitonin gene‐related peptide (CGRP) and pituitary adenylate cyclase activating peptide (PACAP).
Endotoxin, injected intravitreally, evoked inflammatory responses, i.e. conjunctival hyperaemia, miosis and protein extravasation, reflected by the aqueous flare response (AFR). In control rabbits, the maximum AFR was 66.5 ± 9.5 (arbitrary units). Pretreatment with the NO synthase (NOS) inhibitor, NG‐nitro‐l‐arginine (L‐NAME, 200 mg kg−1) given by intravenous injection, inhibited the endotoxin‐evoked responses; the AFR was 16.5 ± 1.9 (n = 8, P < 0.001) and the conjunctival hyperaemia was abolished.
Endotoxin‐evoked ocular inflammation is associated with the release of CGRP and PACAP from C‐fibres. In the eyes challenged with endotoxin, the concentrations of PACAP‐27, −38 and CGRP in the aqueous humour were 58.2 ± 10.9, 54.4 ± 12.4 and 5526 ± 519 (pmoll−1), respectively. L‐NAME inhibited the release of PACAP‐27, −38 and CGRP; the concentrations were 14.3 ± 2.5, 13.5 ± 2.5 and 510 ± 67 (pmoll−1), respectively (n = 8, P < 0.01 or 0.001).
Intravitreal injection of 0.3 nmol CGRP induced conjunctival hyperaemia and AFR; the maximum AFR was 140.2 ± 11.4. L‐NAME suppressed the response induced by CGRP; the AFR was 23.4 ± 5.5 (n = 8, P < 0.001). L‐NAME abolished the conjunctival hyperaemia induced by PACAP‐27 and −38 (0.3 nmol) and reduced the AFR.
The inflammatory cells that infiltrated the uvea, cornea and aqueous humour in large numbers in response to intravitreal injection of endotoxin were found to express inducible NOS. L‐NAME prevented the appearance of such cells.
Our findings suggest that NO plays an important role in the endotoxin‐evoked ocular inflammation in the rabbit: NO activates C‐fibres causing release of C‐fibre neuropeptides into the aqueous humour. In addition, NO mediates some of the ocular effects of CGRP and PACAP, since L‐NAME suppressed the AFR induced by these peptides.
Clonidine‐induced increase in osmolar clearance and free water clearance via activation of two distinct α2‐adrenoceptor sites
Authors: Intengan H.D. , Smyth D.D. 
Published: July 2012

Clonidine, an α2‐adrenoceptor agonist, will increase urine flow rate in the anaesthetized rat by increasing both free water and osmolar clearance. In the present study, we investigated whether these effects of clonidine were mediated at two sites which could be distinguished pharmacologically in uninephrectomized male Sprague‐Dawley rats.
Clonidine (1.0 nmol kg−1 min−1) infused into the renal artery increased osmolar and free water clearance. Following pretreatment with prazosin (0.15 mg kg−1, i.v.), an antagonist with reported selectivity for the α2b‐adrenoceptor subtype, the increase in free water but not osmolar clearance was decreased. Pretreatment with the opioid receptor antagonist, naltrexone (3.0 mg kg−1, i.v.) attenuated the increase in osmolar but not free water clearance. This disparate antagonism of clonidine by prazosin and naltrexone was consistent with two distinct sites.
We submit the hypothesis that the α2a‐ and α2b‐adrenoceptor subtypes mediated the clonidine‐induced osmolar and free water clearance. The blockade in free water clearance by prazosin indicated a possible role of the α2b‐adrenoceptor subtype whereas the α2a‐adrenoceptor subtype was considered as the site mediating the clonidine‐induced increase in osmolar clearance. UK‐14,304 (1.0 nmol kg−1 min−1), a mixed α2‐adrenoceptor/imidazoline receptor agonist with selectivity for the α2a‐subtype, increased only osmolar clearance. This increase was blocked by naltrexone but not prazosin pretreatment. The imidazoline receptor was not involved, as naltrexone failed to alter the moxonidine (3.0 nmol kg−1‐min−1) induced increase in osmolar clearance. These data suggested to us that the α2a‐/α2b‐subtype hypothesis should be investigated more closely in future studies.
These findings indicate that the increase in osmolar and free water clearance following clonidine can be distinguished pharmacologically indicating that two sites were involved. Furthermore, we propose the hypothesis that the α2a‐adrenoceptor subtype mediated osmolar clearance whereas the α2b‐subtype mediated free water clearance. The prazosin‐sensitive increase in free water clearance following clonidine suggested a possible role for the α2b‐subtype. The naltrexone‐sensitive increase in osmolar clearance following clonidine and UK‐14,304 (but not moxonidine) suggested a possible role of the α2a‐subtype. Clearly, this postulate requires further study.
Protective action of hydroxyethyl rutosides on singlet oxygen challenged cardiomyocytes
Authors: Olbrich Hans‐Georg , Grabisch Peter , Großmann Alexander , Rinne Thorsten , Klepzig Harald , Mutschler Ernst 
Published: July 2012

The effect of a standardized mixture of β‐hydroxyethyl rutosides against oxidative damage in singlet oxygen‐challenged isolated cardiac myocytes from adult rats was investigated. The morphology of the myocytes was evaluated as an indicator for cell viability (elongated, rod shaped cells vs. hypercontracted, rounded cells). The determination of the production of thiobarbituric acid reactive substances served as an indicator for lipid peroxidation.
Exposure to singlet oxygen which was generated by photo‐excitation of rose bengal (10−7 m) reduced the number of rod shaped (vital) cardiomyocytes by 78.5 ± 2.5% and increased the production of thiobarbituric acid reactive substances by 1180 ± 150% in comparison to incubation with control buffer.
Coincubation of the cells with β‐hydroxyethyl rutosides (concentration range: 6.7 pg ml−1 to 670 μg ml−1) increased the number of rod shaped cardiomyocytes after exposure to singlet oxygen in a dose‐dependent bell‐shaped manner. A significant protective effect was observed at β‐hydroxyethyl rutosides concentrations ranging from 0.67 ng ml−1 to 67 ng ml−1.
In spite of their protective action, β‐hydroxyethyl rutosides did not reduce the accumulation of thiobarbituric acid reactive substances, used as an indicator for lipid peroxidation.
The data suggest that β‐hydroxyethyl rutosides exert a protective action against oxygen radical‐induced damage of cardiac myocytes at very low concentrations without interfering with lipid peroxidation.
Effects of cytochrome P450 inhibitors on potassium currents and mechanical activity in rat portal vein
Authors: Edwards Gillian , Zygmunt Peter M. , Högestätt Edward D. , Weston Arthur H. 
Published: July 2012

The effects of the cytochrome P450 inhibitors, proadifen, clotrimazole and 17‐octadecynoic acid (17‐ODYA) on K‐currents in freshly‐isolated single cells derived from rat portal vein and on mechanical activity in whole veins were studied.
When cells were stepped from −90 mV to a series of test potentials (from −80 to +50 mV), a delayed rectifier current (IK(V)) and an A‐type current (IK(A)) could be identified. Proadifen (10 μm), clotrimazole (30 μm) and 17‐ODYA (5 μm) each inhibited IK(A) but had little effect on IK(A).
When cells were held at −10 mV to inactivate the time‐dependent K‐currents, IK(V) and IK(A), levcromakalim (3 μm) induced a time‐independent outward K‐current (IK(ATP)) which was totally inhibited by clotrimazole (30 μm) and almost fully inhibited by proadifen (10 μm). 17‐ODYA (5 μm) had no effect on IK(ATP) and exerted only a minor inhibitory action on this current at 20 μm.
17‐ODYA (5 μm) potentiated current flow through the large conductance, Ca‐sensitive K‐channel (BKCa). In contrast, proadifen (10 μm) had no effect on IBK(Ca) whereas clotrimazole (30 μm) exerted a small but significant inhibitory action.
Proadifen (10 μm) and clotrimazole (30 μm) each inhibited the magnitude but increased the frequency of spontaneous contractions in whole portal veins. 17‐ODYA (5 μm) had no effect on spontaneous contractions but these were inhibited when the concentration of 17‐ODYA was increased to 50 μm.
The spasmolytic effect of levcromakalim on spontaneous contractions was antagonized by proadifen (10–30 μm) in a concentration‐dependent manner but 17‐ODYA (up to 50 μm) was without effect.
These results in portal vein show that cytochrome P450 inhibitors exert profound effects on a variety of K‐channel subtypes. This suggests that enzymes dependent on this cofactor may be important regulators of K‐channel activity in smooth muscle. The relevance of these findings for the identification of the pathway involved in the synthesis of the endothelium‐derived hyperpolarizing factor is discussed.