bluuebunny/crossref_metadata_2025_split huggingface dataset:
Depression of miniature endplate potential frequency by acetylcholine and its analogues in frog
Authors: Nikolsky E.E. , Bukharaeva E.A. , Strunsky E.G. , Vyskočil F. 
Published: July 2012

Acetylcholine (ACh), 7.5 × 10−5 m, and carbachol, 5 × 10−6m (CCh) depressed the frequency of miniature endplate potentials (m.e.p.ps) in the frog (Rana temporaria) sartorious neuromuscular junction with active acetylcholinesterase to about 50–55% of the controls.
A similar depression was produced by the nicotinic agonists, nicotine, suberyldicholine and tetramethylammonium.
The muscarinic agonists, oxotremorine, methylfurmethide and methacholine were without effect on m.e.p.p. frequency. The muscarinic antagonist, atropine and the nicotinic antagonist, (+)‐tubocurarine, had no effect on the depression of m.e.p.p. frequency evoked by CCh.
The ganglionic blockers, benzhexonium and IEM‐1119, were also without effect on the CCh‐evoked depression of m.e.p.p. frequency.
Pretreatment of muscles with anticholinesterases did not prevent the CCh‐induced drop in m.e.p.p. frequency.
The effect of CCh was proportionally the same as in the controls in preparations where the m.e.p.p. frequency was changed by elevation of K+ and in the presence of theophylline, noradrenaline, dibutyryl adenosine 3′:5′‐cyclic monophosphate (db cyclic AMP) and db cyclic GMP.
An inhibitor of Na+,K+‐ATPase, ouabain, 5 × 10−5 mol l−1, prevented or reversed the depression of m.e.p.p. frequency by CCh. However, the depression was present in a nominally K+‐free medium. Insulin and adrenaline, which are considered to be Na+,K+‐ATPase activators, were without effect on depression of m.e.p.p. frequency.
The depression of m.e.p.p. frequency by 5 × 10−6 m CCh was the same at temperatures between 5 and 30°C with a Q10 near to 1.0. When threshold amounts of CCh were used (6 × 10−7 and 3 × 10−7 m), the depression was less at higher temperatures.
The receptive structures responsible for the CCh (or ACh)‐evoked depression of m.e.p.p. frequency differ pharmacologically from muscarinic, nicotinic ganglionic and neuromuscular junction ACh‐receptors as well as from the synaptic cholinesterase, in contrast to previous reports (Duncan & Publicover, 1979). The low temperature‐dependence points to the possibility that physical rather than biochemical processes are limiting in this presynaptic effect of cholinomimetics.;
Estimation of the efficacy and affinity of the β2‐adrenoceptor agonist salmeterol in guinea‐pig trachea
Authors: Dougall I.G. , Harper D. , Jackson D.M. , Leff P. 
Published: July 2012

We have attempted to estimate the affinity and efficacy of the new β2‐adrenoceptor agonist salmeterol in the guinea‐pig isolated trachea and to compare these estimates with those obtained for salbutamol.
The kinetics of the relaxation to salmeterol were considerably slower than those to salbutamol and the responses were poorly defined. Nevertheless, in experiments employing a cumulative curve design both salmeterol and salbutamol exhibited partial agonist behaviour. Operational model‐fitting of these data indicated that the intrinsic efficacies of the two agonists were indistinguishable but that salmeterol had an affinity (pKA = 7.4) some 30 fold greater than salbutamol (pKA = 5.9).
Single dose experiments, using maximally effective concentrations of salmeterol or salbutamol were carried out in an attempt to quantify more reliably the relative efficacies of the two agonists. In these experiments salbutamol was found to have an efficacy (2.5) approximately 3 fold greater than that of salmeterol (0.8).
Full/partial agonist interaction studies were carried out to provide another estimate of the affinity of salmeterol. Isoprenaline and adrenaline were employed as full agonists in these experiments and the affinity (pKB) estimates obtained for salmeterol against these agonists were 7.3 and 7.4 respectively. These affinity estimates were similar to the pKA value (7.4) obtained by operational model‐fitting.
Salmeterol has slightly lower efficacy (3 fold) but markedly greater affinity (30 fold) than salbutamol at β2‐receptors. The slightly lower efficacy of salmeterol is unlikely to have clinical implications for this drug as a bronchodilator β2‐adrenoceptor agonist in asthma.;
Multiple effects of ryanodine on intracellular free Ca2+ in smooth muscle cells from bovine and porcine coronary artery: modulation of sarcoplasmic reticulum function
Authors: Wagner‐Mann Colette , Hu Qicheng , Sturek Michael 
Published: July 2012

The effects of ryanodine and caffeine on intracellular free Ca2+ concentration ([Ca2+]i) were studied by use of fura‐2 microfluorometry in single smooth muscle cells freshly dispersed from bovine and porcine coronary artery.
Bovine and porcine cells demonstrated similar sensitivities to 10 min of exposure to ryanodine in physiological salt solution (PSS), as determined by comparable dose‐dependent decreases in the subsequent [Ca2+]i transient induced by 5 mm caffeine.
Ryanodine (10 μm) caused a significant increase in [Ca2+]i to a plateau level 27 ± 3% and 38 ± 4% above baseline [Ca2+]i (baseline [Ca2+]i = [Ca2+]i at 0 min) in porcine and bovine cells, respectively, when bathed in PSS. In bovine cells the time required to reach ½ the plateau level was only 3 min versus 6 min for porcine cells.
The ryanodine‐induced plateau increase in [Ca2+]i was 35 ± 5% above baseline for bovine cells bathed in 0 Ca PSS (PSS including 10 μm EGTA with no added Ca2+), but only 7 ± 3% above baseline in porcine cells during 10 min exposure to 10 μm ryanodine. In bovine cells [Ca2+]i showed proportional increases when extracellular Ca2+ was increased from the normal 2 mm Ca2+ PSS to 5 and 10 mm.
Cells pretreated with caffeine in 0 Ca PSS, which depleted the caffeine‐sensitive sarcoplasmic reticulum Ca2+ store, showed no increase in [Ca2+]i when challenged with 10 μm ryanodine. The ryanodine‐associated increase in [Ca2+]i, which was sustained in 0 Ca PSS during the 10 min ryanodine exposure in cells not pretreated with caffeine, suggests that ryanodine releases Ca2+ from the sarcoplasmic reticulum, but also inhibits Ca2+ efflux.
Intracellular free Ba2+ ([Ba2+]i) was measured with fura‐2 microfluorometry to define further the Ca2+ efflux pathway inhibited by ryanodine; specifically, Ba2+ is not transported by the Ca2+ pump, but will substitute for Ca2+ in Na+‐Ca2+ exchange. In porcine cells pretreated with caffeine in 0 Ca PSS to deplete the caffeine‐sensitive sarcoplasmic reticulum Ca2+ store, depolarization with 80 mm K+ in 2 mm external Ba2+ caused a 100 ± 6% increase in fura‐2 fluorescence ([Ba2+]i). During the 17.5 min 0 Ca PSS recovery from depolarization, exposure to 10 μm ryanodine inhibited the removal of [Ba2+]i by 69 ± 3% when compared with control (0 Ca PSS without ryanodine).
It was concluded that in bovine and porcine smooth muscle cells: (a) ryanodine (≥ 10 μm) releases Ca2+ from the sarcoplasmic reticulum; (b) ryanodine (≥ 10 μm) decreases Ca2+ efflux, probably by inhibition of Na+‐Ca2+ exchange; (c) the sarcoplasmic reticulum Ca2+ store may be larger in bovine than in porcine smooth muscle cells; thus, porcine cells have a relatively greater reliance on Ca2+ influx to increase [Ca2+]i.
Effects of BRL 38227 on neurally‐mediated responses in the guinea‐pig isolated bronchus
Authors: Good D.M. , Clapham J.C. , Hamilton T.C. 
Published: July 2012

In guinea‐pig isolated bronchus treated with indomethacin (2.8 μm), electrical field stimulation (EFS; 10 Hz, 0.5 ms, 60–70 V, for 10 s) evoked a tetrodotoxin (3 μm)‐sensitive, biphasic contraction comprising a rapid, atropine (1 μm)‐sensitive cholinergic response succeeded by a slowly developing, capsaicin (10 μm)‐sensitive, non‐adrenergic, non‐cholinergic excitatory (NANCe) response.
BRL 38227 (0.3–3 μm), salmeterol (0.003–3 μm) and ketotifen (1.0–300 μm) each produced concentration‐dependent inhibition of both NANCe and cholinergic responses to EFS in guinea‐pig isolated bronchus.
Substance P (SP; 1 μm) and neurokinin A (NKA; 0.07 μm) produced contractions equivalent in magnitude to the NANCe response to EFS, which were inhibited by salmeterol (1 μm), but not by BRL 38227 (3 μm) or ketotifen (100 μm).
Acetylcholine (ACh; 6 μm) was equi‐effective with the electrical activation of cholinergic neurones. BRL 38227 (3 μm) slightly inhibited responses to ACh (6 μm). Salmeterol (1 μm) and ketotifen (100 μm) markedly inhibited responses to ACh (6 μm).
In bronchial rings pre‐contracted with ACh (100 μm), BRL 38227 (0.1– 30 μm), salmeterol (0.001–3 μm) and ketotifen (0.1–100 μm) each produced concentration‐dependent relaxation. Unlike ketotifen, BRL 38227 and salmeterol only partially (18.8 ± 2.1% and 51.8 ± 3.9% respectively) reversed the ACh‐induced contraction.
The (+)‐analogue of BRL 38227, BRL 38226 (0.3–100 μm), was without effect on responses to EFS and had no effect on the inhibition caused by BRL 38227. The K+‐channel activators pinacidil (3.0–30 μm) and RP 52891 (3.0–30 μm) exerted similar inhibitory actions on responses to EFS as BRL 38227, but were less potent. Glibenclamide (0.1–1.0 μm) and phentolamine (3 μm) antagonized the inhibitory effects of BRL 38227 on responses to EFS.
It is concluded that BRL 38227 and ketotifen can inhibit NANCe neuroeffector transmission at concentrations exerting little or no inhibitory effects on responses to exogenously applied tachykinins. By contrast, in addition to suppressing NANCe responses to EFS, salmeterol also markedly inhibits responses to SP and NKA. At concentrations markedly suppressing cholinergic neuroeffector transmission, BRL 38227 has only minor effects on responses to exogenously‐applied ACh. Salmeterol and ketotifen both depress responses to ACh within the concentration‐range over which they inhibit cholinergic responses to EFS. The inhibitory effects of BRL 38227 on responses to EFS exhibit stereo‐specificity and may involve the opening of a neuronal K+‐channel. This K+‐channel is glibenclamide‐ and phentolamine‐sensitive and appears similar to the smooth muscle K+‐channel which is modulated by BRL 38227.
Endothelium‐dependent increase in vascular sensitivity to phenylephrine in long‐term streptozotocin diabetic rat aorta
Authors: Chang Kyoung S.K. , Stevens Wendell C. 
Published: July 2012

The effect of short‐ and long‐term streptozotocin (STZ)‐induced diabetes (12 and 52 weeks) on the vascular response to phenylephrine was examined in the isolated thoracic aorta with and without intact endothelium from diabetic, age matched control rats and diabetic rats treated with insulin.
Twelve weeks after induction of diabetes, aortae with intact endothelium demonstrated no changes either in sensitivity (defined as pD2) or contractility (defined as the maximal developed tension per aortic tissue wet weight) to phenylephrine.
In contrast, 52 weeks after induction of diabetes, aortae with intact endothelium demonstrated an increased sensitivity to phenylephrine while contractility to phenylephrine was not changed. Insulin treatment partially corrected the increased sensitivity to phenylephrine observed in diabetic rat aorta.
Removal of endothelium abolished the difference in phenylephrine sensitivity between diabetic and control aortae at 52 weeks.
Pretreatment of intact aortae with methylene blue, an inhibitor of endothelium‐derived relaxing factor (EDRF), abolished the difference in phenylephrine sensitivity between control and diabetic rat aortae at 52 weeks, while pretreatment with indomethacin, an inhibitor of cyclo‐oxygenase, had no effect. These results suggest that decreases in production or release of EDRF might be responsible for the increased vascular sensitivity to phenylephrine observed in long‐term STZ diabetic rats.
Acetylcholine‐induced relaxation, which is EDRF‐dependent, was less in diabetic rat aortae with intact endothelium at 52 weeks, but not at 12 weeks. These results further support the theory that decreases in capacity of the endothelium to synthesize or release EDRF may occur in long‐term STZ diabetic rats.
Lack of effect of potassium channel openers on ATP‐modulated potassium channels recorded from rat ventromedial hypothalamic neurones
Authors: Sellers A.J. , Boden P.R. , Ashford M.L.J. 
Published: July 2012

Single neuronal cells were freshly isolated from the ventromedial hypothalamic nuclei (VMHN) of the rat brain. Currents through ATP‐modulated and large conductance (160 and 250 pS) calcium‐activated potassium channels were recorded by the cell‐attached and excised inside‐out patch techniques.
BRL38227 (lemakalim; 30–90 μm) applied to the superfusing medium produced no change in firing rate of isolated glucose‐receptive VMHN neurones in cell‐attached recordings.
BRL38227, at concentrations of between 30–100 μm applied to the intracellular (cytoplasmic) aspect of inside‐out patches, had no effect on the activity of ATP‐sensitive K+ channels in the absence of ATP or in the presence of a sub‐maximal inhibitory concentration (3 mm) of ATP. Cromakalim, pinacidil, minoxidil sulphate and diazoxide also produced no effect under these conditions.
The potassium channel openers (KCO's) were tested on ATP‐activated potassium channels recorded from a further subpopulation of VMHN neurones. Application of BRL38227 (up to and including 100 μm) to this channel in inside‐out patches either in the absence of ATP or when activated by 5 mm ATP had no effect on channel activity. Identical results were obtained with cromakalim and pinacidil.
BRL38227 had no effect on either of the large conductance (250 pS and 160 pS) calcium‐activated potassium channels in VMHN neurones.
Intracellular recordings were made from glucose‐receptive VMHN neurones in rat brain slices. Cromakalim (50 μm) or diazoxide (60 μm) did not alter the firing rate or passive membrane properties of these neurones demonstrated to be sensitive to tolbutamide (0.1 mm).
These results show that the KCO's tested in this study have no effect either on VMHN neurones contained in brain slices or on the activity of any of the ATP‐modulated potassium channels under isolated patch conditions associated with these neurones.
l‐Leucyl‐l‐arginine, naltrindole and d‐arginine block antinociception elicited by l‐arginine in mice with carrageenin‐induced hyperalgesia
Authors: Kawabata Atsufumi , Nishimura Yumiko , Takagi Hiroshi 
Published: July 2012

Intraplantar injection of carrageenin into the mouse hind paw produced hyperalgesia when measured by the paw pressure test (Randall & Selitto method).
Subcutaneous administration of l‐arginine (100–1,000 mg kg−1), a possible precursor of kyotorphin which is an endogenous analgesic neuropeptide, inhibited carrageenin‐induced hyperalgesia in a dose‐dependent manner. This effect was blocked by subcutaneous administration of naloxone, naltrindole, a selective δ‐opioid receptor antagonist (enkephalin antagonist), and d‐arginine.
Intracerebroventricular administration of l‐leucyl‐l‐arginine inhibited the antinociceptive effect of systemically administered l‐arginine in hyperalgesic mice.
Intracerebroventricular administration of l‐arginine (3 and 30 μg per mouse) and kyotorphin (300 ng − 3 μg per mouse) produced antinociception in hyperalgesic mice. The antinociceptive effects of l‐arginine but not kyotorphin were blocked by intracerebroventricular administration of d‐arginine.
These results suggest that l‐arginine‐induced antinociception is mediated by activation of ‘kyotorphinergic’ nerves followed by activation of the ‘opioidergic’ (possible ‘enkephalinergic’) nerves in the central nervous system.
Characterization of endothelium‐dependent relaxations resistant to nitro‐l‐arginine in the porcine coronary artery
Authors: Nagao Tetsuhiko , Vanhoutte Paul M. 
Published: July 2012

Previous studies, demonstrated that endothelium‐dependent relaxations which are resistant to nitro‐l‐arginine (an inhibitor of nitric oxide synthase) are accompanied by membrane hyperpolarization in the porcine coronary artery. The present experiments were designed to characterize further this type of endothelium‐dependent relaxation in response to bradykinin by measuring isometric force in isolated rings of that artery. The experiments were performed in the presence of indomethacin to rule out vasoactive prostanoids.
Bradykinin induced comparable endothelium‐dependent relaxations of proximal and distal rings of porcine coronary arteries contracted with prostaglandin F2α in the presence of nitro‐l‐arginine.
Bradykinin and SIN 1 (a donor of nitric oxide) reduced contractions induced by prostaglandin F2α in an additive fashion in the presence of nitro‐l‐arginine.
Bradykinin (in the presence of nitro‐l‐arginine) relaxed the tissues contracted with tetraethylammonium, prostaglandin F2α, phorbol 12, 13‐diacetate or endothelin, with similar pD2 values.
The time course of the relaxations induced by bradykinin (in the presence of nitro‐l‐arginine) and UK 14304 (an α2‐adrenoceptor agonist, in the absence of the inhibitor of nitric oxide synthase) were comparable.
These results suggest that, in the porcine coronary artery, nitro‐l‐arginine‐resistant relaxations (a) are distributed similarly in the proximal and distal parts of the artery, (b) contribute to inhibition of vascular smooth muscle with nitric oxide in an additive fashion, (c) occur during contractions induced by various contractile agents and (d) do not precede those mediated by nitric oxide.
Subclassification of release‐regulating α2‐autoreceptors in human brain cortex
Authors: Raiteri Maurizio , Bonanno Giambattista , Maura Guido , Pende Mario , Andrioli Gian Carlo , Ruelle Antonio 
Published: July 2012

Release‐regulating α2‐autoreceptors in human brain were characterized pharmacologically in cortical slices from patients undergoing neurosurgery to remove subcortical tumours; the slices were prelabelled with [3H]‐noradrenaline ([3H]‐NA) and stimulated electrically (3 Hz, 2 ms, 24 mA) under superfusion conditions.
The stimulus‐evoked tritium overflow was almost totally Ca2+‐dependent and tetrodotoxin‐sensitive.
Clonidine and oxymetazoline 0.01 to 1 μm inhibited in a concentration‐dependent manner the evoked overflow of tritium. The two drugs were equipotent (EC50 = 0.03 μm) and their maximal effect was approx. 45%. Phenylephrine and methoxamine, up to 1 μm, did not affect tritium overflow.
Yohimbine (0.01–0.1 μm) shifted the concentration‐response curve of clonidine to the right. The calculated pA2 value was 8.29.
Prazosin and 2‐[2‐[4‐(o‐methoxyphenyl)piperazine‐1‐yl]ethyl]‐4,4‐dimethyl‐1,3(2H,4H)‐isoquinolinedione (AR‐C 239), tested at 0.3 μm, did not modify the concentration‐response curve of clonidine.
The effect of clonidine was antagonized by (+)‐mianserin (pA2 = 7.74), but not by up to 0.3 μm of the (−)‐enantiomer. The concentration‐response curve of clonidine was shifted to the right by the novel α2‐adrenoceptor antagonist, 5‐chloro‐4‐(1‐butyl‐1,2,5,6‐tetrahydropyridin‐3‐yl)‐thiazole‐2‐amine (Z)‐2‐butenedioate (1:1) salt (ORG 20350) (pA2 = 7.55).
Yohimbine, (+)‐mianserin and ORG 20350, but not prazosin and (−)‐mianserin, increased the electrically‐evoked tritium overflow, suggesting that autoreceptors may be tonically activated by endogenous NA.
Desipramine (1 μm) increased evoked tritium overflow from human cortex slices. The effect of clonidine (0.01 − 1 μm) on the evoked overflow of tritium was reduced in presence of 1 μm desipramine.
It is proposed that autoregulation of NA release can occur in human cerebral cortex. The process involves activation of α2‐adrenoceptors which may be either the α2A or the α2D subtype.
One way cross tolerance between cromakalim and salbutamol in the uterus of the rat in vivo
Authors: Downing Sandra J. , Hollingsworth Michael 
Published: July 2012

Cross tolerance between the potassium (K+) channel opener, cromakalim and the β2‐adrenoceptor agonist, salbutamol, was investigated in the uterus of the non‐pregnant rat in vivo. Uterine sensitivity to salbutamol was similar in both vehicle‐treated and cromakalim‐tolerant rats. In salbutamol‐tolerant rats, uterine responses to cromakalim were markedly decreased compared with saline‐infused rats, such that maximum inhibition of uterine contractions was less than 40%.
Propranolol treatment and salbutamol tolerance each produced similar reductions in sensitivity of the uterus to salbutamol of approximately 10 fold. The same dose of propranolol did not influence uterine sensitivity to cromakalim, which suggests that the relaxant action of cromakalim is not due to a direct or indirect activation of uterine β2‐adrenoceptors.
Salbutamol produced a marked (11.7 fold) increase in uterine adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) concentrations measured ex vivo, which was completely inhibited by propranolol pretreatment, but was unaffected by glibenclamide pretreatment. Cromakalim did not increase uterine cyclic AMP concentrations, suggesting that stimulation of adenylate cyclase is not significant in the uterine relaxant action of cromakalim.
The lack of propranolol antagonism of cromakalim and of cromakalim‐induced changes in uterine cyclic AMP concentrations suggests that the cross tolerance observed between salbutamol and cromakalim may be at the level of K+‐channels.
Platelet‐activating factor relaxes ferret tracheal smooth muscle and reduces transepithelial potential difference in vitro
Authors: Webber S.E. , Morikawa T. , Widdicombe J.G. 
Published: July 2012

The effects of platelet activating factor (PAF) were examined on the smooth muscle tone, mucus volume, lysozyme and albumin outputs and potential difference (PD) across the ferret tracheal wall.
PAF (0.1–10 μm) had no direct effect on mucus volume, lysozyme or albumin output from the ferret trachea. PAF produced concentration‐dependent relaxations of the tracheal smooth muscle and reductions in PD across the tracheal wall. There was no change in the histological appearance of the trachea after exposure to PAF.
The PAF‐induced smooth muscle relaxation was not affected by FPL55712, a combination of mepyramine and cimetidine, or by a combination of the oxygen free‐radical scavengers catalase and superoxide dismutase (SOD); but was abolished by indomethacin or the PAF‐receptor antagonist WEB2086.
The PAF‐induced reduction in PD was not affected by indomethacin, FPL55712 or mepyramine and cimetidine, but was prevented by catalase and SOD, and by WEB2086.
We conclude that PAF relaxes ferret tracheal smooth muscle in vitro by receptor‐mediated release of a bronchodilator prostaglandin, possibly PGE2. PAF also reduces PD across the trachea suggesting changes in epithelial function; however, there is no histological epithelial damage after PAF. The reduction in PD with PAF is probably produced by receptor‐mediated release of oxygen free‐radicals. The cellular source of these free‐radicals and of the dilator prostaglandin is unclear.