bluuebunny/crossref_metadata_2025 huggingface dataset:
Caffeine‐evoked, calcium‐sensitive membrane currents in rabbit aortic endothelial cells
Authors: Rusko J. , Van Slooten G. , Adams D.J.
Published: July 2012

Single cell photometry and whole‐cell patch clamp recording were used to study caffeine‐induced intracellular Ca2+ signals and membrane currents, respectively, in endothelial cells freshly dissociated from rabbit aorta.

Caffeine (5 mM) evoked a transient increase in [Ca2+]i in fura‐2‐loaded endothelial cells. Pretreatment of cells with lO μM ryanodine did not alter resting [Ca2+]i but irreversibly inhibited the caffeine‐induced rise in [Ca2+]i. The caffeine‐induced increase in [Ca2+]i was not attenuated by the removal of extracellular Ca2+ and did not stimulate the rate of Mn2+ quench of fura‐2 fluorescence.

Bath application of caffeine evoked a dose‐ and voltage‐dependent outward current. The rate of onset and amplitude of the caffeine‐evoked outward current increased with higher caffeine concentrations and membrane depolarization. The relationship between caffeine‐evoked current amplitude and membrane potential was non linear, suggesting that the channels underlying the current are voltage‐sensitive.

In the absence of extracellular Ca2+, the amplitude of the caffeine‐evoked outward current was reduced by approximately 50% but the duration of the current was prolonged compared to that observed in the presence of external Ca2+. Ca2+‐free external solutions produced an unexpected increase in both the frequency and amplitude of spontaneous transient outward currents (STOCs).

Inclusion of heparin (10 μg ml−1) in the patch pipette abolished the acetylcholine (ACh)‐induced outward current but failed to inhibit either STOCs or the caffeine‐evoked outward current in native endothelial cells. In the absence of extracellular Ca2+, heparin did not affect either STOCs or the caffeine‐induced outward current.

Externally applied tetraethylammonium ions (TEA, 3–10 mM) reversibly inhibited unitary Ca2+‐activated K+ currents and STOCs in endothelial cells but failed to inhibit completely the outward current evoked by 20 mM caffeine.

Bath application of 0.1 mM zinc ion (Zn2+), a chloride channel blocker, did not affect unitary currents or STOCs but reduced the amplitude of the caffeine‐evoked current by >75% compared to control. Replacement of extracellular NaCl with Na gluconate also reduced the amplitude of the caffeine‐induced outward current. Bath application of 0.1 mM Zn2+ and 10 mM TEA completely blocked the caffeine‐evoked outward current in endothelial cells.

Caffeine‐induced Ca2+ release from intracellular stores evokes a transient rise in [Ca2+]i which is correlated with a large, transient outward current. The ionic dependence and inhibition of the caffeine‐sensitive current by TEA and Zn2+ suggests that Ca2+‐activated K+ and Cl− conductances contribute to the caffeine response in rabbit aortic endothelial cells.
Characterization of α1‐adrenoceptor subtypes in tension response of human prostate to electrical field stimulation
Authors: Guh Jih‐Hwa , Chueh Shih‐Chieh , Ko Feng‐Nien , Teng Che‐Ming
Published: July 2012

The effects of various α1‐adrenoceptor antagonists and nifedipine on tension responses of human prostate to electrical field stimulation were evaluated in this study.

Prazosin (3 × 10−10 to 10−8M) and 5‐methyl‐urapidil (10−9 to 3 × 10−8 M) blocked concentration‐dependently the tension responses to electrical field stimulation and completely abolished them in the maximal concentrations (10−8 M and 3 × 10−8 M, respectively); in contrast, chloroethylclonidine (CEC), in the maximal concentration of 100 μM, blocked these effects by only 50%.

The contractile responses of rat vas deferens and spleen to exogenously‐applied α1radrenoceptor agonists were competitively inhibited by prazosin and 5‐methyl‐urapidil; in addition, the pA2 values were calculated and the relative potencies with reference to prazosin were obtained. The relative potency of 5‐methyl‐urapidil in human prostate (0.105) was close to that in rat vas deferens (0.257), which contains primarily putative α1A‐adrenoceptors. However, it was much more than that in rat spleen (0.011), which contains primarily putative α1B‐adrenoceptors.

Nifedipine (10−8 to 10−6 M) inhibited concentration‐dependently the contractile responses to electrical field stimulation in human prostate; in addition, the inhibition percentages were similar to those to exogenously‐applied noradrenaline in rat vas deferens. In contrast, CEC (10 μM), which almost flattened the concentration‐response curve of the rat spleen to phenylephrine, only partially inhibited (by 33.1%) the nerve‐mediated contraction of human prostate.

The involvement of prejunctional α2‐adrenoceptors situated on the sympathetic nerve terminals of human prostate was also examined. Clonidine (3 × 10−9 to 3 × 10−7 M) blocked concentration‐dependently the contractile response to electrical field stimulation of human prostate and this inhibitory effect was reversed by yohimbine (10−7 M). Additionally, the inhibitory effect of CEC (3 × 10−6 to 3 × 10−4 M) to the nerve‐mediated contraction was also partially reversed by yohimbine (10−7M).

It is suggested that the putative α1A‐adrenoceptors in human prostate may be functionally confined to the synaptic region whereas only minor populations of the putative α1B‐ and/or αlc‐adrenoceptors exist in this region.
Pharmacological identification of different inhibitory mediators involved in the innervation of the internal anal sphincter
Authors: Tottrup A. , Knudsen M.A. , Sorensen F. Hanberg , Glavind E.B.
Published: July 2012

Inhibitory non‐adrenergic, non‐cholinergic (NANC) responses were studied in isolated strips from the rabbit internal anal sphincter.

In the presence of atropine and guanethidine, transmural field stimulation induced frequency‐dependent relaxations that reached a plateau at frequencies ≥ 4 Hz.

These relaxations were inhibited by apamin (10−6M) and by Nω‐nitro‐L‐arginine (L‐NOARG, 10−4M). With these two substances in combination, relaxations were still seen in response to field stimulation, but only at frequencies >2Hz.

In the presence of both apamin (10−6 M) and L‐NOARG (10−4 M), responses at high frequencies consisted of a fast relaxation followed by a slow return to prestimulus tension level. α‐Chrymotrypsin hastens the return of tension to prestimulus level after high frequency stimulation.

Zinc‐protoporphyrin IX, an inhibitor of haeme oxygenase, had a significant inhibitory effect on relaxations induced by transmural field stimulation. It was found, however, that responses to sodium nitroprusside and to isoprenaline (both 10−9‐10−4M) were reduced comparably, indicating that the effect of zinc‐protoporphyrin IX was unspecific.

It is concluded that pharmacological analysis allows identification of at least three distinguishable components of the inhibitory NANC innervation of the rabbit internal anal sphincter. The study does not allow conclusions about the role of carbon monoxide, a recently proposed mediator of NANC responses in opossum internal anal sphincter.
Inhibition by zinc protoporphyrin‐IX of receptor‐mediated relaxation of the rat aorta in a manner distinct from inhibition of haem oxygenase
Authors: Ny Lars , Andersson Karl‐Erik , Grundemar Lars
Published: July 2012

Carbon monoxide (CO), produced by haem oxygenase through degradation of haem, has been claimed to be a neuromessenger and a possible regulator of vascular tone. We examined whether the haem oxygenase inhibitor, zinc protoporphyrin‐IX (ZnPP) and other porphyrins affect the relaxation evoked by various agents in the rat isolated aorta.

Pretreatment with ZnPP (0.1 mM) virtually abolished the relaxation evoked by vasoactive intestinal peptide (VIP) and atrial natriuretic peptide (ANP). ZnPP also evoked a rightward shift of the concentration‐response curve for the relaxation induced by acetylcholine.

In contrast, ZnPP did not affect the relaxation evoked by forskolin and 3‐morpholino‐sydnonimine, agents which directly activate adenylate and guanylate cyclase, respectively.

Although, less effective than ZnPP, tin protoporphyrin‐IX (SnPP; 0.1 mM) and protoporphyrin‐IX (PP; 0.1 mM) also attenuated the VIP‐evoked relaxation.

The elevation of cyclic AMP and cyclic GMP levels evoked by VIP and ANP, respectively, were abolished by pretreatment with ZnPP (0.1 mM).

ZnPP, SnPP and PP did not affect the contraction evoked by phenylephrine.

The results show that ZnPP inhibits relaxation induced by VIP, ANP and acetylcholine, probably by interfering with membrane receptor‐coupled signal transduction pathways. This inhibition does not seem to be dependent upon inhibition of haem oxygenase. The lack of specificity of the haem oxygenase inhibiting metalloporphyrins makes them less suitable as pharmacological tools in the investigation of a messenger role for CO.
ETA receptor‐mediated constrictor responses to endothelin peptides in human blood vessels in vitro
Authors: Maguire Janet J. , Davenport Anthony P.
Published: July 2012

We have characterized the constrictor endothelin receptors present in human isolated blood vessels using ETA and ETB selective agonists and antagonists.

Monophasic dose‐response curves were obtained for ET‐1 with EC50 values of 6.8 nM in coronary artery, 3.9 nM in internal mammary artery, 17.4 nM in pulmonary artery, 14.5 nM in aorta and 3.2 nM in saphenous vein. In coronary artery, ET‐2 was equipotent with ET‐1 with an EC50 value of 5.7 nM. The non‐selective peptide, sarafotoxin 6b, was 2–3 times less potent than ET‐1 but the maximum responses to these two were comparable.

In each vessel ET‐3 was much less active than ET‐1. No response was obtained to ET‐3 in aorta and pulmonary artery or in up to 50% of coronary artery, mammary artery and saphenous vein preparations. In those preparations that did respond, dose‐response curves were incomplete at 300 nM. Variable contractions were also obtained with the ETB‐selective agonist, sarafotoxin 6c (S6c). Where responses were detected, although S6c was more potent than ET‐1 (EC50 values of 0.6‐1.2 nM), the maximum response produced was always less than 20% of that to ET‐1.

The synthetic ETB agonists, BQ3020 and [l,3,11,15Ala]‐ET‐l, were without effect in any of the five blood vessels at concentrations up to 3 μM.

ET‐1‐induced vasoconstriction was blocked by the ETA‐selective antagonists, BQ123 and FR139317. Schild‐derived pA2 values were 7.0, 7.4 and 6.9 for BQ123 and 7.6, 7.9 and 7.3 for FR139317 in coronary artery, mammary artery and saphenous vein, respectively, consistent with antagonism of ETA receptors. Slopes of the Schild regressions were not significantly different from one. Comparable values of pA2 were estimated for 3 μM BQ123 in aorta (7.4 ±0.5) and pulmonary artery (6.9) from the Gaddum‐Schild equation.

In conclusion we have shown that in human isolated blood vessels, ET‐1 is more potent than ET‐3 suggesting the presence of vasoconstrictor ETA receptors. This is supported by the lack of effect of the ETB agonists, BQ3020 and [1,3,11,15Ala]‐ET‐l and the ability of the ETA antagonists, BQ123 and FR 139317 to block ET‐1 responses. Some preparations did contract in response to low concentrations of the ETB‐selective sarafotoxin 6c but responses were variable and the maximum was always much less than that to ET‐1 in the same preparations. Therefore although constrictor ETB receptors were present on the smooth muscle of human blood vessels, vasoconstriction elicited by the endothelin peptides in vitro is via ETA receptor activation.
Inhibitory action of betaxolol, a β‐selective adrenoceptor antagonist, on voltage‐dependent calcium channels in guinea‐pig artery and vein
Authors: Setoguchi Motoko , Ohya Yusuke , Abe Isao , Fujishima Masatoshi
Published: July 2012

The effects of betaxolol, (±)‐l‐[4‐[2‐(cyclopropylmethoxy) ethyl] phenoxy]‐3‐(isopropylamino)‐2‐propanol hydrochloride, a β1‐selective adrenoceptor antagonist, on voltage‐dependent Ca2+ channels were investigated in single smooth muscle cells from guinea‐pig mesenteric artery and portal vein using a whole‐cell variant of the patch‐clamp technique. Ca2+ channel currents were recorded with bath solutions contained 10 mM Ba2+ for arterial cells and 2mMCa2+ for venous cells.

Betaxolol inhibited Ca2+ channel currents dose‐dependently in both mesenteric artery cells and portal vein cells. The two isomers, (+)‐betaxolol and (−)−betaxolol (relative β‐antagonistic efficacies of 0.1 and 1, respectively), had similar potencies for inhibiting Ca2+ channel currents in portal vein cells. Propranolol did not inhibit the currents. Thus the inhibitory action of betaxolol on Ca2+ channel currents was independent of the β‐adrenoceptor.

The inhibitory action of betaxolol on Ca2+ channel currents was compared with that of diltiazem and of nifedipine in mesenteric artery cells. The current inhibition depended on the stimulation frequency with all drugs (use‐dependent block). All drugs also accelerated the current decay and shifted the voltage‐dependent inactivation curve in a negative direction.

In conclusion, betaxolol inhibited Ca2+ channel currents in vascular smooth muscle cells. The mode of inhibitory action was similar to that of diltiazem and nifedipine. Our results suggest that betaxolol is a unique β‐adrenoceptor antagonist that has a direct inhibitory action on voltage‐dependent Ca2+ channels in vascular smooth muscle cells.
SPECIAL REPORT Noradrenaline‐induced relaxation of rat oesophageal muscularis mucosae: mediation solely by innervated β3‐adrenoceptors
Authors: de Boer Robert E.P. , Brouwer Frans , Zaagsma Johan
Published: July 2012

We investigated the effects of cocaine and corticosterone on the noradrenaline‐induced relaxation of rat oesophageal smooth muscle in the absence and presence of the selective β2‐antagonist, ICI 118,551. It was found that the concentration‐response curve (CRC) of noradrenaline was not shifted by ICI 118,551 at 1 μM, whereas a clear shift to the right was observed at 100 μM of the antagonist. In the presence of corticosterone (10 μm), CRCs were clearly shifted to the left; with cocaine (10 μM) additionally present, a further leftward shift was observed, indicating the involvement of both neuronal and extraneuronal uptake sites. It was concluded that the relaxation of rat oesophageal muscularis mucosae by noradrenaline is solely mediated by β3‐adrenoceptors which are sympathetically innervated.
Electrophysiological actions of felbamate on rat striatal neurones
Authors: Pisani Antonio , Stefani Alessandro , Siniscalchi Antonio , Mercuri Nicola B. , Bemardi Giorgio , Calabresi Paolo
Published: July 2012

We have investigated the effects of the anticonvulsant drug, felbamate (FBM), on striatal neurones, recorded in vitro by using both intracellular and extracellular conventional recordings in slices and whole‐cell recordings in acutely isolated neurones.

FBM, at therapeutically relevant concentrations (30–300 μM) showed multiple mechanisms of action. Like other antiepileptic drugs, FBM (30–300 μM) showed a direct inhibitory action on current‐evoked firing discharge of striatal neurones. A patch‐clamp analysis of this effect revealed a dose‐related reduction of voltage‐dependent sodium (Na+) currents (10–100 μM), with a half inhibition dose (IC50) value of 28 μM.

We also tested whether FBM affected corticostriatal glutamatergic transmission. In control medium (1.2 mM external magnesium), both extracellularly recorded field potentials and intracellularly recorded excitatory postsynaptic potentials (e.p.s.ps) evoked by cortical stimulation were not affected by bath application of 30–300 μM FBM.

When magnesium was removed from the perfusing solution, a procedure which reveals a N‐methyl‐D‐aspartate (NMDA)‐mediated component in the corticostriatal synaptic potential, FBM (30–300 μm) produced a dose‐dependent reduction of the amplitude of both the field potential and the e.p.s.p.

FBM reduced the inward currents produced either by bath or by focal applications of 30 μM NMDA, a finding consistent with the hypothesis that the observed reduction of the NMDA‐mediated component of the synaptic potentials may be caused at postsynaptic level.

The reduction of the NMDA‐mediated component of the synaptic transmission by FBM and its depressant effect on the voltage‐dependent Na+ channels, may account for the antiepileptic action of this drug. Moreover, the pharmacological properties of FBM might render this drug interesting as a neuroprotectant agent.
Differential effects of fibrates on the acyl composition of microsomal phospholipids in rats
Authors: Vázquez Manuel , Muñoz Sonia , Alegret Marta , Adzet Tomás , Merlos Manuel , Laguna Juan C.
Published: July 2012

The time‐course and comparative effects of treatment with clofibrate (CFB), bezafibrate (BFB), and gemfibrozil (GFB) on the acyl composition of the main microsomal phospholipids, i.e. phosphatidylchoβ line and phosphatidylethanolamine, have been studied in male Sprague‐Dawley rats.

The administration of the three fibrates caused a strong peroxisomal induction and a hypolipidaemic effect. Concerning the changes in acyl composition, CFB and BFB behaved in a similar way, with differences which could be attributed to their different potency as peroxisome inducers, whereas GFB showed a somewhat distinct profile.

The three drugs increased the relative content of palmitic, palmitoleic and oleic acids, whereas the levels of stearic acid and also those of long chain, highly unsaturated fatty acids docosatetraenoic, docosapentaenoic and docosahexaenoic acids were reduced. In general, these effects appeared from the first day of treatment and were highly correlated with peroxisomal proliferation. In addition, they were more evident in the phosphatidylcholine than in the phosphatidylethanolamine fraction.

Fibrates increased total monounsaturated fatty acids, whereas a decrease in total polyunsaturated fatty acids in the phosphatidylcholine fraction was observed in CFB‐ and BFB‐, but not in GFB‐treated rats. Clear differences appeared between CFB and BFB on the one hand, and GFB on the other when the influence of fibrate treatment on the molar percentages of linoleic, eicosatrienoic, arachidonic and mead acids was analyzed.

GFB increased linoleic acid content in phosphatidylethanolamine, whereas CFB and BFB decreased its level in both phospholipid fractions. In contrast, CFB and BFB enhanced eicosatrienoic and mead acids in both fractions and arachidonic acid in phosphatidylethanolamine, whereas GFB had practically no effect.

The different behaviour of GFB may be explained on the basis of two different observations. First, GFB is the weakest peroxisomal inducer of the three fibrates tested. Second, GFB is the strongest inhibitor in vitro of some of the enzyme activities related to fatty acid chain modelling, particularly elongases and desaturases.
New high affinity peptide antagonists to the spinal galanin receptor
Authors: Xu Xiao‐Jun , Wiesenfeld‐Hallin Zsuzsanna , Langel Ülo , Bedecs Katarina , Bartfai Tamás
Published: July 2012

The role of endogenous galanin in somatosensory processing has been studied with galanin receptor antagonists. The new galanin receptor ligands C7, M32, M38 and M40 bind with high affinity (Kd in nanomolar range) to spinal cord galanin receptors and possess oxidative stability as compared to earlier generations of peptide ligands. These peptides have been examined in the spinal flexor reflex model where exogenous galanin exhibited biphasic excitatory and inhibitory effects.

Intrathecal administration of C7 [galanin(l‐13)‐spantide] and M32 [galanin (1–13)‐neuropeptide Y(25–36) amide] blocked facilitation of the nociceptive flexor reflex induced by 30 pmol intrathecal galanin in decerebrate, spinalized rats in a dose‐dependent manner, thus behaving as antagonists of the galanin receptor. In contrast, M38 [galanin(l‐13)‐(Ala‐Leu)3‐Ala amide] and M40 [galanin(l‐13)‐Pro‐Pro‐(Ala‐Leu)2‐Ala amide], exhibited only weak antagonism at high doses in this model. Moreover, lower doses of M40 potentiated galanin‐induced reflex facilitation. C7 was neurotoxic at high doses in the rat spinal cord.

M32 and C7 were potent antagonists of galanin receptors in rat spinal cord, in correlation with their in vitro binding characteristics. In contrast, M38 and M40, despite their high in vitro affinity, exhibited only very weak antagonism. Moreover, M40 may also behave as a partial agonist.

Previous studies have shown that the galanin receptor may be heterogeneous. The discrepancy between in vitro binding and in vivo antagonistic potency of M38 and M40 may also suggest the presence of different galanin receptor subtypes within the rat spinal cord. However, other explanations for the discrepancy, such as differences in metabolic stability, diffusion rates and penetration to the site of action are also possible.
SPECIAL REPORT: Protective effect of NO on gastric lesions and inhibition of expression of gastric inducible NOS by flurbiprofen and its nitro‐derivative, nitroflurbiprofen
Authors: Mariotto S. , Menegazzi M. , de Prati A. Carcereri , Cuzzolin L. , Adami A. , Suzuki H. , Benoni G.
Published: July 2012

Nitroflurbiprofen (NFP) causes significantly less gastric lesions than flurbiprofen (FP), probably because of its capacity to release nitric oxide (NO) in the stomach. Lipopolysaccharide (LPS), which induces the expression of an inducible type of NO synthase (iNOS) in rat stomach, also reduces gastric mucosal damage elicited by FP. Furthermore, both FP and NFP decrease significantly the amount of mRNA encoding iNOS induced by LPS in the stomach. The inhibitory effect of NFP seems to be due at least in part to its ability to release NO.
RS‐45041‐190: a selective, high‐affinity ligand for I2 imidazoline receptors
Authors: Brown C.M. , MacKinnon A.C. , Redfern W.S. , Williams A. , Linton C. , Stewart M. , Clague R.U. , Clark R. , Spedding M.
Published: July 2012

RS‐45041‐190 (4‐chloro‐2‐(imidazolin‐2‐yl)isoindoUne) showed high affinity for I2 imidazoline receptors labelled by [3H]‐idazoxan in rat (pKi = 8.66 ±0.09), rabbit (pKi = 9.37 ± 0.07), dog (pKi = 9.32±0.18) and baboon kidney (pKi = 8.85 ±0.12), but had very low affinity for α2‐adrenoceptors in rat cerebral cortex (pKi = 5.7 ± 0.09)

RS‐45041‐190 showed low affinity for other adrenoceptors, dopamine, 5‐hydroxytryptamine, and muscarinic receptors and dihydropyridine binding sites (selectivity ratio > 1000)

RS‐45041‐190 showed moderate potency for the inhibition of monoamine oxidase A in vitro (pIC50 = 6.12), but had much lower potency for monoamine oxidase B (pIC50 = 4.47), neither of which equated with its affinity for I2 receptors

RS‐45041‐190 (0.001 to 3 mg kg−1, i.v. and 1 ng‐50 μ i.e.v.) had only small, transient effects on blood pressure and heart rate in anaesthetized rats. In conscious rats, RS‐45041‐190 had no effect on body core temperature or tail skin temperature (1 mg kg−1, s.c.) or on activity or rotarod performance (10 mg kg−1, i.p.). There were also no effects on barbiturate sleeping time in mice after doses of 1–10 mg kg−1, i.p

RS‐45041‐190 (10 and 25 mg kg−1, i.p.) significantly increased food consumption in rats for up to 4 h after dosing, but unlike idazoxan (10 mg kg−1, i.p.) did not increase water consumption

RS‐45041‐190 is therefore a selective, high‐affinity ligand at I2 imidazoline receptors and its hyperphagic effect may suggest a role for I2 imidazoline receptors in the modulation of appetite. However, in the absence of a selective agonist it is unclear whether this ligand is an agonist or an antagonist at I2 receptors.
Nitric oxide, an enteric nonadrenergic‐noncholinergic relaxant transmitter: evidence using phosphodiesterase V and nitric oxide synthase inhibition
Authors: Williams S.J. , Parsons M.E.
Published: July 2012

The effects of NG‐nitro‐L‐arginine (L‐NOARG), a nitric oxide synthase inhibitor, and SK&F 96231, a phosphodiesterase type V inhibitor, on electrical field stimulated (EFS) nonadrenergic noncholinergic (NANC) relaxations of rat fundal strips, guinea‐pig isolated ileum longitudinal muscle with intact myenteric plexus, and guinea‐pig taenia caeci were investigated

Reproducible repeated control random EFS frequency‐response curves were obtained for all three tissues

> Depending on the frequency of stimulation, L‐NOARG (10−4‐5 × 10−3M) caused either a complete or partial inhibition of the NANC‐induced relaxations of the rat fundal strips and the guinea‐pig isolated ileum longitudinal muscle with intact myenteric plexus, but not of the guinea‐pig taenia caeci. The inhibitory action of L‐NOARG was partially or totally reversed, depending on the tissue, by L‐arginine (5 × 10−3 M)

SK&F 96231 (10−6‐10−4M) caused a concentration‐ and frequency‐dependent potentiation of both the size and duration of the EFS‐induced NANC relaxant response of rat fundal strips and guinea‐pig isolated ileum longitudinal muscle with intact myenteric plexus, but not of the guinea‐pig taenia caeci

Zaprinast, another phosphodiesterase type V inhibitor (10−6‐10−4 M) caused a concentration‐ and frequency‐dependent potentiation of the NANC relaxant responses to EFS of rat fundal strips

SK&F 96231 and zaprinast alone (10−6‐10−4M) caused a concentration‐dependent relaxation of the agonist‐induced tone of all three tissues with the maximum degree of relaxation found to be in the order stomach < ileum < caecum. This is the reverse order for ability of SK&F 96231 to potentiate relaxant responses to EFS

These results suggest NO is involved in the NANC nerve‐mediated relaxation of rat fundal strips and guinea‐pig isolated ileum longitudinal muscle with intact myenteric plexus, but not the guinea‐pig taenia caeci.
Inhibition of angiogenesis, tumour growth and metastasis by the NO‐releasing vasodilators, isosorbide mononitrate and dinitrate
Authors: Pipili‐Synetos Eva , Papageorgiou A. , Sakkoula Eleni , Sotiropoulou Georgia , Fotsis T. , Karakiulakis G. , Maragoudakis M.E.
Published: July 2012

The effect of the nitric oxide (NO)‐producing nitrovasodilators isosorbide mononitrate (ISMN) and isosorbide dinitrate (ISDN) were assessed on (a) the in vivo model of angiogenesis of the chick chorioallantoic membrane (CAM) and (b) on the growth and metastatic properties of the Lewis Lung carcinoma (LLC) in mice

Isosorbide 5‐mononitrate (ISMN) and isosorbide dinitrate (ISDN), inhibited angiogenesis in the CAM dose‐dependently. ISMN was more potent in inhibiting this process. Both compounds were capable of completely reversing the angiogenic effect of α‐thrombin. These effects of ISMN and ISDN on angiogenesis were comparable to those previously observed with sodium nitroprusside which generates NO non‐enzymatically

Mice, implanted intramuscularly with LLC, received daily i.p. injections of ISMN for 14 days resulting in a significant decrease in the size of the primary tumour and a reduction in the number and size of metastatic foci in the lungs. ISDN had a similar but less pronounced effect than that observed with ISMN

Addition of ISMN or ISDN to cultures of bovine, rabbit and human endothelial cells and to cultures of LLC cells had no effect on their growth characteristics

These results indicate that ISMN and ISDN inhibit angiogenesis and tumour growth and metastasis in an animal tumour model. The possibility should therefore be considered that these nitrovasodilators which are widely used therapeutically and have well characterized pharmacological profiles, may also possess antitumour properties in the clinic.
Enhancement by benzodiazepines of the inhibitory effect of adenosine on skeletal neuromuscular transmission
Authors: Chiou L.C. , Ling J. Y. , Chang C.C.
Published: July 2012

Interactions of benzodiazepines with adenosine on the neuromuscular transmission were studied in mouse diaphragm preparations

In tubocurarine (0.6‐0.8 μm)‐partially paralyzed preparations, diazepam (35 μm) and Ro 5–4864 (3∼30 μm), a peripheral type benzodiazepine receptor agonist, potentiated the inhibitory effect of adenosine on indirect twitch responses

The central type receptor agonist, clonazepam did not affect the inhibitory effect of adenosine

The peripheral benzodiazepine receptor antagonist, PK11195 (1–10 μm) attenuated the adenosine inhibition and antagonized the potentiation by Ro 5–4864

Ro 5–4864 failed to enhance further the inhibitory effect of adenosine in the presence of dipyridamole, an adenosine uptake inhibitor that also potentiated adenosine inhibition

Neither Ro 5–4864 nor PK 11195 affected the inhibition produced by a stable adenosine analogue, 2‐chloroadenosine, which is not a substrate for the adenosine uptake system

Ro 5–4864 did not affect endplate potentials (e.p.ps) in the absence of adenosine, but reduced the amplitude of e.p.ps in the presence of adenosine without affecting miniature e.p.ps

It is suggested that benzodiazepines potentiate the adenosine‐effected presynaptic inhibition of neuromuscular transmission by an inhibition of adenosine uptake through activation of peripheral type benzodiazepine receptors.
Pharmacological modulation of adrenal medullary GABAA receptor: consistent with its subunit composition
Authors: Parramón M. , González M.P.
Published: July 2012

Muscimol, the specific GABAA receptor agonist, increased the secretion of catecholamines by chromaffin cells with an EC50 of 2.9 ± 0.4 μm

GABAA receptors of these cells were modulated by the same drugs which modulate GABAA receptors in brain tissue

Benzodiazepines enhanced muscimol‐evoked catecholamine secretion by between 20 and 80%. This effect seems to be mediated by binding to a central type of benzodiazepine receptor because it was completely blocked by the specific antagonist, Ro 15 1788. This antagonist was able to displace [3H]‐flunitrazepam binding with an EC50 of 0.26 ±0.05 nM

β‐Carbolines weakly inhibited muscimol‐induced catecholamine secretion and were able to displace [3H]‐flunitrazepam binding with an EC50 between 0.2 and 0.9 nM, depending on the β‐carboline used.

Pregnanolone and related neuroactive steroids enhanced muscimol‐evoked catecholamine secretion by up to 87%, in a dose‐dependent fashion. In contrast pregnenolone weakly inhibited muscimol‐evoked catecholamine secretion

Zn2+ did not affect GABAA receptor‐induced catecholamine secretion

These pharmacological results are absolutely concordant with the theoretical properties given by the GABAA receptor subunit composition of bovine adrenal medulla ‐α1 α4, β1–3, γ2‐ previously characterized by Western blot analysis.
Modulation of calcium channel currents by arachidonic acid in single smooth muscle cells from vas deferens of the guinea‐pig
Authors: Nagano Norihiro , Watanabe Minora
Published: July 2012

Effects of arachidonic acid (AA) on voltage‐dependent Ca channel currents were investigated by whole‐cell‐clamp methods in single smooth muscle cells freshly isolated from vas deferens of the guinea‐pig

Ca channel current was decreased by application of 1–30 μm AA in a concentration‐dependent manner. When Ca2+ or Ba2+ was the charge carrier, Ca channel current (ICa or IBa) was reduced by AA to a similar extent (IC50= 10 and 6 μm, respectively). Addition of 15 mM BAPTA to the pipette solution did not affect the reduction of IBa by 10 μm AA

The effect of AA on IBa was not prevented by internal application of 1 mM nordihydroguaiaretic acid (NDGA) and 1 mM indomethacin (Indo). When the pipette solution contained 0.1 mM guanosine‐5′‐triphosphate (GTP), IBa was decreased slightly but significantly by application of 30 (M prostaglandin (PGF2α) but not by PGE2. This effect of PGF2α was irreversible or not observed when the pipette solution contained 0.3 mM guanosine‐5′‐(3‐thiotriphosphate) (GTPγS) or both GTP or guanosine‐5′‐0‐(2‐thiodiphosphate) (GDPβS), respectively

External application of 100 units ml−1 superoxide dismutase slightly but significantly attenuated the inhibition of IBa by 1–30 μm AA. Intracellular application of 1 mM GDPβS or 0.3 mM GTPγS did not significantly change the effect of AA. Intracellular application of 0.1 mM 1‐(5‐isoquinolinesulphonyl)‐2‐methylepiperazine (H‐7) also did not change the effect of AA

These results indicate that the decrease in Ca channel currents in vas deferens smooth muscle cells is mainly due to AA itself, as opposed to its metabolites. The effect of AA may be due to AA itself, as opposed to its metabolites. The effect of AA may be due to its direct action on Ca channels or membrane phospholipids, but may not be mediated by activation of GTP binding proteins or protein kinase C. The inhibition of Ca channel current by AA may be partly induced by superoxide radicals derived from AA oxidation. PGF2α also reduces Ca channel currents but probably by a separate mechanism via activation of a GTP binding protein.
Cardiovascular responses to intrathecal neuropeptide γ in conscious rats: receptor characterization and mechanism of action
Authors: Poulat Philippe , de Champlain Jacques , Couture Réjean
Published: July 2012

In the conscious rat, cardiovascular responses to intrathecally (i.t.) administered neuropeptide γ (NPγ) were studied prior to and after the i.t. pretreatment with selective antagonists at NKi ((±)‐CP 96345 and RP 67580), NK2 (SR 48968) and NK3 (R 486) receptors. Pretreatment with a mixture of peptidase inhibitors (phosphoramidon, captopril, bacitracin, phenanthroline) was also tested to ascertain whether or not the effect of NPγ was mediated by a metabolite. The involvement of peripheral catecholamines was examined with intravenous injection of α‐adrenoceptor (phentolamine) and β‐adrenoceptor (propranolol) antagonists.

NPγ (0.078‐78 nmol) induced dose‐dependent increases in heart rate (HR) and mean arterial blood pressure (MAP). The highest dose of 78 nmol did not induce an increase of MAP greater than that with 7.8 nmol but was preceded by a transient decrease of MAP (1–3 min). No desensitization was observed when three injections of 7.8 nmol NPγ were given at 90 min intervals.

Cardiovascular and behavioural (biting/scratching) effects evoked by 0.78 nmol NPγ were significantly reduced by the NK1 antagonists, (±)‐CP 96345 (65 nmol) or RP 67580 (7.8 and 78 nmol). However, cardiovascular responses to NPγ were not affected by (±)‐CP 96345 (6.5 nmol), SR 48968 (7.8 and 78 nmol) or R 486 (25 nmol). Pretreatment with peptidase inhibitors significantly enhanced the cardiovascular and behavioural responses to NPγ.

The pressor response to 7.8 nmol NPγ was converted to a vasodepressor response by pretreatment with phentolamine (2 mg kg−1, i.v.) while the chronotropic response was markedly reduced by propranolol (2 mg kg−1, i.v.).

These results suggest that the cardiovascular responses to i.t. NPγ are mediated by NK1 receptors in the spinal cord leading to the peripheral release of catecholamines from sympathetic fibres or the adrenal medulla. It is unlikely that the spinal action of NPγ results from its metabolic conversion into neurokinin A or another major metabolite.
Alterations in the force‐frequency relationship by tert‐ butylbenzohydroquinone, a putative SR Ca2+ pump inhibitor, in rabbit and rat ventricular muscle
Authors: Baudet S. , Do E. , Noireaud J. , Le Marec H.
Published: July 2012

The effects of 2,5 di‐(tert‐butyl)‐1,4‐benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, on twitch tension, time course and SR Ca2+ content have been studied at different stimulation frequencies (0.5‐3 Hz) in isolated preparations from the rabbit and rat right ventricle, at 37°C.

At 0.5Hz, 30 μm TBQ induced a marked negative inotropic effect in both species (— 57% in the rabbit and —68% in the rat) and decreased the rate of rise and fall of twitch tension. In parallel, SR Ca2+ content (assessed by rapid cooling contractures) was depressed in the rabbit by 42%. The force‐frequency relationship (positive for the rabbit and negative for the rat) was significantly attenuated. In the rabbit, this alteration was shown to rely on insufficient SR Ca2+ reloading with increasing frequencies.

Exposure of TBQ‐treated preparations to 8 mM extracellular Ca2+ or 5 μm isoprenaline were effective in reloading the SR with Ca2+ whereas 20 mM caffeine emptied this compartment.

In the rabbit ventricle, increase in stimulation frequency shortened control twitch time course by decreasing both the time to peak tension (TTP) and the time to half relaxation (t1/2). TBQ did not differentially affect the pattern for t1/2 but significantly attenuated the frequency‐induced decrease of TTP.

In rabbit ventricular muscle, the action potential duration increased between 0.5 and 3 Hz whether or not TBQ was present. However, TBQ induced a small but significant additional action potential shortening.

TBQ decreased twitch tension in the rat ventricle between 0.5 and 3 Hz but the negative staircase was not differentially affected by the SR Ca2+ pump inhibitor. In control conditions and in the presence of 30 μm TBQ, t1/2 was frequency‐independent but TBQ consistently increased this parameter (by ∽ 29%).

These data argue in favour of a specific and partial inhibition of the SR Ca2+ pump by 30 μm TBQ in the rabbit and rat ventricle and emphasise the importance of SR Ca2+ uptake in the force‐frequency phenomenon.
Differential effects of tert‐butyl‐benzohydroquinone, a putative SR Ca2+ pump inhibitor, on isometric relaxation during the staircase in the rabbit and rat ventricle
Authors: Baudet S. , Noireaud J. , Le Marec H. , Khammari A.
Published: July 2012

The effects of 2,5 di‐(tert‐butyl)‐1,4‐benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum Ca2+ pump, on mechanical relaxation and contraction‐relaxation coupling have been studied at different frequencies (0.5‐3 Hz) in isometrically contracting isolated right ventricular preparations of rabbit and rat at 37°C. Two types of mechanical responses have been studied: the twitch tension and the force transient (rewarming spike, RSp) following a rapid cooling contracture (RCC, an index of sarcoplasmic reticulum Ca2+ content) on return to 37°C.

The coupling between contraction and relaxation was assessed by two methods: (a) by evaluation of the variation of the slope relating the maximal rate of tension fall to twitch peak tension; (b) by modelling the twitch according to the following equation: TwT (t) = C x(t/A)Bx exp(1‐(t/AB) where TwT(t) is the time course of isometric tension, t is time, C and A are an inotropic and a chronotropic index respectively and B, a contraction‐relaxation coupling index (Nwasokwa, 1993).

In the rabbit ventricle, 30 μm TBQ did not prevent the frequency‐induced shortening of the twitch time to half‐relaxation (t1/2) and of the time constant (τ) describing the final part of the RSp relaxation (τ decreased from 140 ms (0.5 Hz) to 133 ms (3 Hz) in control and from 253 ms (0.5 Hz) to 197 ms (3 Hz) after exposure to TBQ). By contrast, at a given frequency, the prolongation of relaxation induced by TBQ was proportional to its inotropic effect (unchanged slopes and B values) but TBQ did not prevent the acceleration of relaxation observed at high frequencies: B increased from 2.02 (0.5 Hz) to a peak value of 2.18 (1 Hz) in control and from 1.88 (0.5 Hz) to a maximum of 2.48 (2 Hz) after TBQ exposure. TBQ significantly attenuated the decay of RCCs elicited after increasingly longer periods of muscle quiescence as normally observed in control conditions.

In the rat ventricle, TBQ depressed relaxation more than expected on the basis of its negative inotropic effects (B decreased from 2.16 to 1.84 at 0.5 Hz and from 2.15 to 1.66 at 3 Hz). TBQ also slowed the rate of RSp relaxation (τ increased from 95 ms to 168 ms at 0.5 Hz, and from 109 ms to 149 ms at 3 Hz) and increased twitch t1/2. By contrast with the results obtained in the rabbit ventricle, B, τ and t1/2 were frequency‐insensitive whether or not TBQ was present.

TBQ exerts negative inotropic effects consistent with inhibition of the SR Ca2+ pump. In the rabbit ventricle, the TBQ‐induced potentiation of relaxation acceleration at high pacing frequencies suggests the involvement of counteracting Ca2+‐mediated mechanisms probably via Ca2+‐calmodulin‐activated kinases. In the rat ventricle, TBQ did not have any differential effect on relaxation depending on the frequency, probably because the extent of the negative staircase was small in the present experimental conditions.
Enhanced vasocontraction of rat tail arteries by toxoflavin
Authors: Wang Zunzhe , Ma Meisheng , Wang Rui
Published: July 2012

It has been suggested that the toxic effect of toxoflavin (TXF) produced by Pseudomonas cocovenenas is mainly due to the impairment of electron transfer of the mitochondrial respiratory chain. However, the cardiovascular effect of TXF is unknown. In the present study, the effect of TXF on the isometric contraction of rat isolated tail artery strips and the underlying mechanisms were investigated.

The basal force of the tissues was not affected by the toxin. However, the application of TXF before or during KC1 (60 mM) stimulation potentiated KC1‐induced vasocontraction, specifically the tonic phase of the contraction.

When the vessel strips were precontracted with phenylephrine (Phe), TXF further enhanced the tonic contraction of the tissue. Pretreatment of tissues with TXF also potentiated subsequent vasocontraction induced by Phe. The vasocontractor effects of TXF and Phe, however, were not additive.

The vascular effect of TXF was not mediated by oxygen‐derived free radicals since catalase and SOD did not affect TXF‐enhanced vasocontraction. In contrast, the vasocontractor effect of TXF was dependent on extracellular Ca2+ and abolished by nifedipine (a Ca2+ antagonist). TXF also had no effect on caffeine‐ or U46619‐induced vasocontraction.

It is suggested that TXF may potentially contract blood vessels via its effect on Ca2+ channels. This effect of TXF depends on the contractile status of the vascular tissues.
Involvement of nitric oxide, but not prostaglandins, in the vascular sympathoinhibitory effects of losartan in the pithed spontaneously hypertensive rat
Authors: Richer Christine , Domergue Valérie , Vincent Marie‐Pascale , Giudicelli Jean‐François
Published: July 2012

The aim of this study was to investigate whether nitric oxide (NO) and/or vasodilator prostaglandins (PGs) are involved in the sympathoinhibitory effects exerted by losartan versus the vascular responses elicited by spinal cord electrical stimulation (SCS) in pithed spontaneously hypertensive rats (SHRs).

SHRs were given orally and for 8 days either losartan (10 mg kg−1 daily) or distilled water (controls). After pithing, blood pressure, heart rate, cardiac output, renal and muscular blood flows (pulsed Doppler technique) and the corresponding vascular resistance values were measured or calculated at baseline. Then, animals from both groups were given i.v. either saline, or NG‐nitro‐L‐arginine methyl ester (L‐NAME, 1 mg kg−1), or diclofenac (4 mg kg−1). Thereafter, haemodynamic parameters were determined in the six subgroups of animals in response (a) to SCS at increasing frequencies, and (b) to a noradrenaline bolus injection.

Losartan significantly decreased mean arterial pressure as well as renal and total peripheral resistances. In addition, losartan exhibited strong vascular sympathoinhibitory effects, significantly decreasing the systemic pressor and regional vasoconstrictor responses to SCS, but did not affect those to exogenous noradrenaline. In contrast, SCS‐induced tachycardia was not modified by losartan.

L‐NAME significantly increased total peripheral and regional vascular resistances but did not affect blood pressure and heart rate basal values. L‐NAME potentiated the haemodynamic responses to SCS in control and, to a larger extent, in losartan‐treated SHRs so that, with the exception of the renal vascular bed, the sympathoinhibitory effects of losartan were attenuated in all vascular beds studied. L‐Arginine (300 mg kg−1) caused reversal of L‐NAME effects in both control and losartan‐treated SHRs.

Diclofenac did not affect the basal values of haemodynamic parameters in control and losartan‐treated SHRs. Diclofenac potentiated the pressor and vasoconstrictor responses to SCS and to a similar extent, in both control and losartan‐treated SHRs, so that the sympathoinhibitory effects of losartan were fully maintained.

These results demonstrate that in pithed SHRs: (a) NO but not PGs contribute to the basal vasomotor tone, (b) both NO and PGs attenuate the pressor and vasoconstrictor responses to SCS, (c) NO plays a major role in the vascular sympathoinhibitory effects of losartan, except at the renal level, and (d) endogenous PGs are not involved in these sympathoinhibitory effects.
Vascular reactivity in mesenteric resistance arteries following chronic nitric oxide synthase inhibition in Wistar rats
Authors: Dowell Fiona J. , Henrion Daniel , Duriez Micheline , Michel Jean‐Baptiste
Published: July 2012

Chronic inhibition of nitric oxide synthase (NOS) induces a sustained hypertension in rats. We studied the effects of chronic inhibition on the in vitro vasoreactivity of mesenteric resistance arteries in Wistar rats. We also investigated the effects of acute in vitro NOS inhibition in these vessels.

Acute NOS inhibition (Nω‐nitro‐L‐arginine, L‐NOARG, 10 μm) had no effect on the contractile response to KCl (125 mM), enhanced the response to the phorbol ester, phorbol dibutyrate (1 μm; 69±9% of KCl response, n=6; 38±7% control, n=6, P<0.05), increased sensitivity to phenylephrine (EC50: 1.68±0.14 μm, n=5; 2.35±0.23 μm control, n=5, P<0.05) and sodium nitroprusside (SNP; EC50 1.79±0.61 nM, n=6; 20.44±6.87 μm control, n=6, P<0.05) and decreased sensitivity to acetylcholine (EC50 123±12 nM, n=6; 45±10 nM control, n=13, P<0.05).

In contrast, contractile responses to KCl (125 mM; 170±12 mN mm−3, n=10; 257±21 mN mm−3 in control, n=13, P<0.005) and phenylephrine (maximum response, 30 μm: 169±24 mN mm−3, n=10; 295±19 mN mm−3 in control, n=13, P<0.001) were significantly reduced in magnitude following chronic NOS inhibition. Sensitivity to phenylephrine was not significantly altered.

The effects of chronic NOS inhibition (Nω‐nitro‐L‐arginine methyl ester, L‐NAME, 10 mg kg−1 daily for 3 weeks) were similar to those of acute NOS blockade with respect to the relaxant responses to SNP and acetylcholine, and also the contraction in response to protein kinase C activation.

Chronic inhibition of NOS significantly increased medial cross sectional area of mesenteric resistance arteries (0.013±0.002 mm2, n=7; 0.009±0.0005 mm2 control, n=15, P<0.05).

Thus, in contrast to the acute effects of NOS inhibition, chronic NOS inhibition results in a down‐regulation of the contractile responses to KCl and phenylephrine in mesenteric resistance arteries, despite an increase in medial cross sectional area. However protein kinase C‐dependent contraction remains relatively enhanced. Endothelium‐dependent relaxation is reduced and endothelium‐independent relaxation is enhanced in a manner similar to the effects of acute NOS blockade.