bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epithelium‐dependent potentiation of anaphylactic contractions by β‐endorphin in tracheae isolated from actively sensitized guinea‐pigs
Authors: Van Oosterhout A.J.M. , Celeda L. , Delsman K.C. , de Wied D. , Nijkamp F.P. 
Published: July 2012

It has been shown that opioid peptides modulate airway function. In the present study, the effect of β‐endorphin on antigen‐induced contractions of isolated tracheal rings from actively sensitized guinea‐pigs has been studied.
β‐Endorphin had a concentration‐dependent bimodal effect on anaphylactic contractions of the trachea. Low concentrations of β‐endorphin (10−10 and 10−8 m) significantly potentiated anaphylactic contractions, whereas higher concentrations (10−7 and 10−6 m) significantly suppressed anaphylactic contractions of guinea‐pig trachea.
β‐Endorphin in concentrations of 10−8 m and 10−7 m did not affect the responsiveness of the tracheal rings to histamine or leukotriene D4. This indicates that β‐endorphin does not influence the responsiveness of tracheal smooth muscle to anaphylactic mediators.
In the presence of the non‐selective opioid receptor antagonist naloxone, 10−8 m β‐endorphin still potentiated the anaphylactic contractions of the trachea. In addition, an equimolar concentration of des‐Tyr1‐β‐endorphin, a fragment of β‐endorphin without opioid‐like activity, also potentiated anaphylactic contractions. The potentiation of anaphylactic contraction by 10−8 m β‐endorphin is not therefore mediated by classical opioid‐receptors.
In the presence of naloxone, 10−7 m, β‐endorphin did not suppress anaphylactic contractions of the trachea. Thus, the suppression of anaphylactic contraction is mediated via a classical opioid‐receptor.
In epithelium‐denuded tracheae, both 10−8 and 10−7 m β‐endorphin suppressed the anaphylactic contractions, whereas 10−8 and 10−7 m des‐Tyr1‐β‐endorphin did not affect anaphylactic contractions. It is concluded that the potentiation of the anaphylactic contraction in intact trachea is epithelium‐dependent whereas the suppression of the anaphylactic contraction is epithelium‐independent.
Time‐dependent synergistic interactions between the vasodilator neuropeptide, calcitonin gene‐related peptide (CGRP) and mediators of inflammation
Authors: Buckley T.L. , Brain S.D. , Rampart M. , Williams T.J. 
Published: July 2012

The action of the long lasting neuropeptide vasodilator, calcitonin gene‐related peptide (CGRP), in potentiating oedema formation and neutrophil accumulation was investigated in the dorsal skin of the rabbit, in vivo. Combinations of agents under test were administered by intradermal (i.d.) injection. Oedema formation and neutrophil accumulation were then measured by quantitative radiolabel techniques.
CGRP (1 × 10−11 mol per site) potentiated neutrophil accumulation induced by zymosan activated plasma, (used as a source of C5a des Arg), N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) and leukotriene B4 (LTB4). In contrast CGRP did not induce neutrophil accumulation when injected alone.
Oedema formation induced by a series of chemically distinct mediators of increased microvascular permeability; bradykinin, platelet activating factor (PAF), FMLP and zymosan‐activated plasma; measured 0–30 min after i.d. injection was potentiated by CGRP (1 × 10−11 mol per site).
Oedema formation induced by zymosan activated plasma and FMLP but not bradykinin and PAF, was also significantly potentiated by CGRP when oedema was measured 30–60 min after i.d. injection. The potentiation of oedema induced by zymosan activated plasma measured 30–60 min after i.d. injection was not observed in the presence of the shorter acting prostanoid vasodilator prostacyclin (PGI2, 3 × 10−10 mol per site).
These results suggest that CGRP, as a consequence of its sustained vasodilator activity could have prolonged potentiating effects on neutrophil accumulation and oedema formation in inflammatory conditions.
Kinetics of (+)‐tubocurarine blockade at the neuromuscular junction
Authors: Le Dain Alexander C. , Madsen Barry W. , Edeson Robert O. 
Published: July 2012

Although (+)‐tubocurarine (Tc) is classically considered to be a competitive antagonist at the neuromuscular junction, kinetic details of the interaction remain unclear.
We studied the competitive action of Tc on the nicotinic receptor at the frog neuromuscular junction using a quantitative analysis of the generation phase of miniature endplate currents (m.e.p.cs) recorded in Ringer solution (20°C) under voltage clamp (–90 mV) in the absence or presence of 1–5 μm Tc. Under control conditions four neurotransmission parameters were estimated by non‐linear regression using a mathematical model of synaptic transmission incorporating transmitter release, diffusion, hydrolysis, receptor binding and channel gating. These parameters were then used in a further regression to estimate binding rate constants for Tc at the same endplate. Allowance was made for open channel block by Tc, which under the conditions of this study was only a small component of total blockade.
The results suggest that Tc binds to the two agonist recognition sites on the nicotinic receptor with equal affinity (stoichiometric KDs of 2.2 and 8.8 μm), and that most of the functional blockade at concentrations up to 5 μm is due to occupancy of only one site.
The association rate constant for Tc binding to sites on the nicotinic acetylcholine receptor appears to be very fast (k+ D = 8.9× 108 m−1 s−1) and comparable to that for acetylcholine (ACh).
In the brief time during which an m.e.p.c. is generated (≅ 200 μs), reversal of Tc blockade by transiently high concentrations of ACh seems to be kinetically limited.
Pressor effects following microinjection of 5‐HT1A receptor agonists into the raphe obscurus of the anaesthetized rat
Authors: Dreteler Gea H. , Wouters Wout , Saxena Pramod R. , Ramage Andrew G. 
Published: July 2012

The effects of electrical stimulation and microinjections (90 nl) of the 5‐HT1A receptor agonists, flesinoxan and 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT), and glutamate into the raphe obscurus on blood pressure, heart rate and phrenic nerve activity (central inspiratory drive) were investigated in rats anaesthetized with α‐chloralose.
Electrical stimulation of the raphe obscurus caused a rise in blood pressure which was associated with bradycardia, while glutamate (2.7 nmol) caused only a rise in blood pressure.
Flesinoxan (1.3 nmol) and 8‐OH‐DPAT (0.7 nmol) increased blood pressure by 9 ± 1 and 14 ± 2 mmHg, respectively and did not affect heart rate. For both agonists the effect on blood pressure was shown to be dose‐dependent; again no effect on the heart rate was observed over the dose‐ranges chosen.
Microinjections of the non‐selective 5‐HT1A receptor antagonists, (±)‐pindolol (2.7 nmol) or methiothepin (5.2 nmol), into the raphe obscurus prevented the increase in blood pressure caused by microinjection of flesinoxan. However, (±)‐pindolol caused a sustained rise in blood pressure of 15 ± 1 mmHg while methiothepin caused a transient rise in blood pressure. Neither drugs affected heart rate. The ability of methiothepin to attenuate the pressor effect of flesinoxan was found to be partially reversed after 30 min.
It is suggested that activation of 5‐HT1A receptors within the raphe obscurus can cause sympathoexcitation.
Radioligand binding to muscarinic receptors of bovine aortic endothelial cells
Authors: Brunner Friedrich , Kukovetz Walter R. 
Published: July 2012

Muscarinic receptors on endothelial cells of bovine thoracic aorta were characterized by binding assays in which (−)‐[3H]‐N‐methyl quinuclidinyl benzilate ([3H]‐NMeQNB) was used as radioligand.
Binding of [3H]‐NMeQNB to crude membranes of freshly isolated endothelial cells was atropine‐displaceable and of high affinity (KD = 0.48 nm) to a single class of sites (maximum binding capacity: 14 ± 3 fmol mg−1 protein). Stereospecificity of the binding sites was demonstrated in experiments in which [3H]‐NMeQNB binding was inhibited by dexetimide in the nanomolar range (KI = 0.63 nm) and by levetimide, its stereoisomer in the micromolar range (KI = 3.2 μm) (selectivity factor: ∼5000).
Drug competition curves indicated a single class of binding sites for antagonists and the following apparant affinities (KI, nm): methyl atropine: 1.1; 4‐diphenylacetoxy N‐methyl piperidine methyl bromide (4‐DAMP): 3.4; pirenzepine: 16; 11‐[2‐(diethylamino‐methyl)‐1‐piperidinyl‐acetyl]‐5,11‐dihydro‐6H‐pyrido(2,3‐b)1,4‐benzodiazepine‐6‐one (AF‐DX 116): 2.500. Competition of acetylcholine with [3H]‐NMeQNB was best described by two affinity sites (or states) (KH = 0.82 μm, KL = 1.6 μm). In the presence of guanylimido diphosphate [Gpp(NH)p] (100 μm), acetylcholine affinity (IC50) was slightly, but significantly reduced (factor ∼4).
Binding of [3H]‐NMeQNB to freshly harvested intact cells was also atropine‐displaceable, stereospecific (selectivity factor: ∼3500) and of high affinity (KD = 0.35 nm). The maximum binding capacity (9 ± 2 fmol mg−1 total cell protein) was comparable to that of membranes and corresponded to ∼900 binding sites per endothelial cell. Binding to enzymatically harvested and cultured endothelial cells, or membranes derived therefrom, showed no atropine‐displaceable binding.
The results suggest that (1) bovine aortic endothelial cells contain muscarinic binding sites with all necessary criteria of functional muscarinic receptors; (2) the receptor most closely corresponds to the M1 subtype and is of comparatively very low density, and (3) cultured endothelial cells lose their receptors during isolation or culture procedures.
Mechanisms underlying the differential sensitivity to a1‐adrenoceptor activation in the bisected rat vas deferens
Authors: Sallés Joan , Badia Albert 
Published: July 2012

The factors underlying the different responsiveness of the prostatic and epididymal portions of rat vas deferens to α1‐adrenoceptor stimulation were investigated.
The α1‐adrenoceptors in membranes of both halves of rat vas deferens were labelled with [3H]‐prazosin and the affinities of agonists and antagonists for these receptors were determined. In saturation studies, the Bmax and KD values for [3H]‐prazosin in membranes of both portions were the same.
In competition studies, the inhibition curves for phentolamine were biphasic and consistent with the presence of both α1a‐ and α1b‐adrenoceptor subtypes. The proportions of binding sites with high and low affinity for phentolamine in both halves of rat vas deferens were similar and in good agreement with the percentages of binding sites for WB‐4101 and phentolamine previously reported in the whole rat vas deferens.
The phenylethylamines displaced [3H]‐prazosin with a shallow inhibition curve. The data are compatible with the assumption of two affinity states for the binding sites. For the imidazoline compounds no such distinct affinity states could be demonstrated.
The affinity for, and the relative intrinsic efficacy on postsynaptic α1‐adrenoceptors of both portions of rat vas deferens were studied for noradrenaline, phenylephrine and methoxamine by irreversible inactivation of the α1‐adrenoceptors by phenoxybenzamine. The parameters for partial agonists were determined by comparing the responses to the partial agonist to those of a full agonist in the same tissue. Homogeneous estimates of the equilibrium dissociation constants (Ka) were obtained, indicating that these agonists bind to the receptors of both tissues in an identical manner. Further, estimation of the intrinsic efficacy of agonists relative to noradrenaline, indicated no differences between the two halves of rat vas deferens.
Ka values for agonist activation of the functional α1‐adrenoceptors were compared with KI values for agonist inhibition of specific [3H]‐prazosin binding. The Ka values were well correlated with the low affinity KI values for phenylethylamines in both portions of rat vas deferens, suggesting that the initial event in signal transduction by α1‐adrenoceptors is the binding to the low affinity state of the receptor.
There was a non‐linear relationship between response and receptor occupancy in both halves of rat vas deferens but the occupancy‐response coupling was more efficient in the epididymal than in the prostatic portion. This fact may account for the differences observed in the functional responses.
Effects of captopril on membrane current and contraction in single ventricular myocytes from guinea‐pig
Authors: Bryant S.M. , Ryder Kathryn O. , Hart G. 
Published: July 2012

Single guinea‐pig ventricular myocytes were voltage‐clamped and cell length was measured with a photodiode array.
Captopril (1 × 10−5 m) reduced both peak early current and active shortening in response to a depolarizing clamp pulse along a similar time course.
From a holding potential of around −45 mV peak early inward current was reduced by 37 ± 9% (P < 0.001) on exposure to captopril. The early current‐voltage relationship was shifted outwards by captopril indicating a reduction in membrane conductance through the L‐type calcium channel (ICa).
The amplitude of cell shortening in response to depolarizing voltage steps was reduced but the voltage‐dependence of contraction after captopril was unchanged.
A small negative shift of the potential at which ICa was half‐activated was observed after captopril. There was no change in the voltage‐dependence of the inactivation variable or in the time‐dependence of repriming for ICa.
The actions of captopril on ICa and developed shortening were dose‐dependent and took place in the same proportion when ICa was increased by isoprenaline.
These results are discussed in relation to the effects of captopril on ICa and contraction and to its clinical usage.
Strychnine‐induced potassium current in isolated dorsal root ganglion cells of the rat
Authors: Aibara K. , Oonuma M. , Akaike N. 
Published: July 2012

Effects of strychnine (Str) on the dissociated dorsal root ganglion (DRG) cells of the rat have been investigated in whole‐cells configuration by a conventional patch‐clamp technique.
γ‐Aminobutyric acid (GABA)‐induced Cl− current (ICl) increased sigmoidally with increasing concentration. The half‐maximal response (Ka) was 3 × 10−5 m and the Hill coefficient was 1.5. Both Str and bicuculline inhibited the GABA‐induced ICl in a concentration‐dependent manner.
Str itself could elicit the current at concentrations over 10−5 m, at which concentrations the GABA response was completely suppressed. The concentration‐response curve for the Str‐induced current was bell‐shaped, and a nearly maximum response occurred at 3 × 10−4 m. A transient ‘hump’ current appeared immediately after the wash‐out of external solution containing high concentrations of Str over
× 10−4 m.
The Str‐induced outward current and a transient ‘hump’ current were augmented by the removal of extracellular K+ and were suppressed by the substitution of intracellular K+ for Cs+. But the current was not sensitive to extracellular Na+, Ca2+ and Cl−.
The reversal potential of Str‐induced current (EStr) was −75 mV, which was close to the K+ equilibrium potential (EK = −76.3 mV). The change of EStr for a ten fold change in extracellular K+ concentration was 58 mV, indicating that the membrane behaves like a K+ electrode in the presence of Str. The reversal potential of the ‘hump’ current was also close to EK.
The Str‐induced outward current was antagonized by K+ channel blockers such as Ba2+, tetraethylammonium (TEA)‐chloride, and 4‐aminopyridine (4‐AP) in a concentration‐dependent manner.
The Str‐induced K+ current was not affected by internal perfusion of bis(γ‐aminophenoxy)ethane‐N,N,N′,N‐tetraacetic acid (BAPTA), indicating that the Str response does not result in the activation of K+ conductance by the intracellular Ca2+.
Calcitonin gene‐related peptide and human epicardial coronary arteries: presence, release and vasodilator effects
Authors: Franco‐Cereceda A. 
Published: July 2012

In the present study, the levels of calcitonin gene‐related peptide (CGRP)‐like immunoreactivity (‐LI) in human cardiopulmonary tissue were determined in combination with studies on CGRP‐LI release from the left anterior descending coronary artery (LAD) and functional effects of CGRP on coronary arterial tone.
The highest levels of CGRP‐LI were found in the LAD followed in declining order by the bronchus, right atrium, pulmonary artery, lung and left ventricle.
Exposure to capsaicin evoked a clear‐cut increase in CGRP‐LI outflow, suggesting release from isolated large specimen of the LAD. This release was Ca2+‐dependent and was markedly attenuated by incubation with the mitochondrial Ca2+‐inhibitor, ruthenium red. Exposure to potassium also released CGRP‐LI in a Ca2+‐dependent fashion from the LAD.
In functional experiments on human epicardial coronary arteries with an inner diameter of 0.4 to 0.8 mm, human CGRP alpha and beta relaxed the potassium‐precontracted arteries equipotently. Substance P (SP) also relaxed these precontracted arteries but the relaxation could be prevented by incubation with methylene blue, an inhibitor of endothelium derived relaxing factor (EDRF)‐mechanisms, which did not influence the effect of CGRP.
Capsaicin evoked a ruthenium red‐sensitive relaxation of the potassium‐precontracted arteries. However, ruthenium red did not affect the relaxations induced by CGRP or SP. Furthermore, the capsaicin effect was not influenced by methylene blue.
It is concluded that CGRP‐LI is present in human cardiopulmonary tissue and can be released upon exposure to high concentrations of capsaicin as well as potassium. CGRP causes relaxation of arteries independently of EDRF activation and closely resembles the vasodilator effects of capsaicin. This supports the view that the coronary vasodilatation observed upon sensory nerve activation is mediated by CGRP. Ruthenium red inhibits capsaicin‐induced CGRP‐LI release and functional effects and may thus serve as an experimental tool in evaluating the function of capsaicin‐evoked stimulation of peripheral nerve terminals.
Characterization of the palytoxin‐induced sodium conductance in frog skeletal muscle
Authors: Ecault Eudes , Sauviat Martin‐Pierre 
Published: July 2012

The effects of palytoxin (PTX) on transmembrane potentials and currents of frog skeletal muscle were analyzed by intracellular microelectrode techniques and the double sucrose‐gap voltage clamp method.
PTX irreversibly depolarized the membrane. The depolarization was Na‐sensitive.
Under voltage clamp, PTX induced an inward resting current which did not inactivate, was inhibited by external Na+ removal and was a function of external Na concentration.
This resting current could be carried either by Na+, Li+, K+ or by guanidinium according to the permeability sequence K+ < Li+ < Na+ < Gua+.
The PTX‐induced current was only weakly sensitive to tetrodotoxin. It was reversibly and dose‐dependently inhibited by amiloride with a one to one stoichiometry and a KD of 0.3 mm.
Acidic pH partially inhibited the current induced by PTX which was also highly sensitive to external Cd2+ and La3+. The inhibitory sequence for divalent cations was: Mg2+ < Ca2+ = Ba2+ = Mn2+ < Cd2+; with La3+ > Cd2+.
The amplitude of the PTX‐induced Irest was markedly reduced in the absence of external Ca2+.
PTX induced a Na+ resting conductance in frog skeletal muscle. The size of the channel induced by PTX is larger than the guanidinium ion. External membrane Ca2+ might be a cofactor involved in the mode of action of PTX.
Influence of lorcainide on microsomal Na+, K+‐ATPase in guinea‐pig isolated heart preparations
Authors: Almotrefi Abdulrahman A. , Dzimiri Nduna 
Published: July 2012

The effects of lorcainide on the myocardial Mg2+‐dependent, Na+ and K+‐activated adenosine triphosphatase (Na+, K+‐ATPase) were compared in guinea‐pig heart preparations with those of ouabain, a specific inhibitor of the enzyme activity.
Both ouabain and lorcainide inhibited the microsomal Na+, K+‐ATPase activity in a concentration‐dependent fashion. Their inhibitory effective ranges were 0.05–100 μm and 0.15–125 μm respectively, and the concentrations for half maximal inhibition (IC50 values) were 2.1 ± 0.3 and 33.5 ± 7.3 μm, respectively.
In a second series of experiments, the combined effects of the two drugs on the enzyme activity were studied. In these experiments, lorcainide produced a concentration‐dependent potentiation of the inhibitory effects of ouabain on Na+, K+‐ATPase activity.
The present study demonstrates that lorcainide is a potent inhibitor of myocardial Na+, K+‐ATPase.
Chemosensitive cardiopulmonary afferents and the haemodynamic response to simulated haemorrhage in conscious rabbits
Authors: Evans Roger G. , Ludbrook John 
Published: July 2012

We set out to test whether the signal from the heart that initiates the decompensatory phase of acute central hypovolaemia in conscious rabbits is conveyed by chemosensitive afferents.
Haemorrhage was simulated by inflating an inferior vena caval cuff so that cardiac output fell at a constant rate of 8% of its baseline level per min. After sham or vehicle treatments the haemodynamic response had two phases. In the first, sympathoexcitatory, phase systemic vascular conductance fell in proportion to cardiac output so that mean arterial pressure fell by only 13 mmHg. When cardiac output had fallen by ∼50% a second, sympathoinhibitory, phase supervened. There was an abrupt rise of systemic vascular conductance and an abrupt fall of mean arterial pressure, to ∼40 mmHg.
The sympathoinhibitory phase was prevented by injection of the δ‐opioid antagonist ICI 174864 (100–300 nmol) or the μ‐opioid agonist H‐Tyr‐d‐Ala‐Gly‐MePhe‐NH(CH2)2OH (DAMGO) (100–300 pmol) into the fourth cerebral ventricle.
5‐HT3 receptors on myocardial or pulmonary afferents were excited by injection of ascending doses of phenylbiguanide (6.25–400 μg) into the left or right atrium respectively. Neuronal‐type nicotinic cholinoceptors in the epicardium were excited by injecting ascending doses of nicotine bitartrate (6.25–400 μg) into the pericardial sac. Each of these treatment regimens caused a reproducible, dose‐dependent, fall in mean arterial pressure. Intravenous injection of the 5‐HT3 antagonist MDL 72222 (1.0 mg kg−1) markedly attenuated the responses to phenylbiguanide. Intrapericardial injection of the neuronal‐type nicotinic cholinoceptor antagonist mecamylamine HCl (0.1 mg kg−1) abolished the effects of intrapericardial nicotine. Neither of these treatments affected the haemodynamic response to simulated haemorrhage.
Injection into the fourth ventricle of ICI 174864 (100–300 nmol) or DAMGO (100–300 pmol) had no effects on the dose‐response relationships for phenylbiguanide or nicotine.
We conclude that the cardiac afferents responsible for initiating the sympathoinhibitory phase of simulated haemorrhage in conscious rabbits do not correspond to the populations of phenylbiguanide‐sensitive cardiopulmonary afferents, nor to the population of nicotine‐sensitive epicardial afferents. We also conclude that the reflex haemodynamic responses to atrial phenylbiguanide and intrapericardial nicotine do not depend on an endogenous δ‐opioid receptor mechanism in the brainstem, and are not affected by exposure of the brainstem to exogeneous DAMGO.