bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison between the pharmacology of dopamine receptors mediating the inhibition of cell firing in rat brain slices through the substantia nigra pars compacta and ventral tegmental area
Authors: Bowery B. , Rothwell L.A. , Seabrook G.R. 
Published: July 2012

Electrophysiological recordings were made from presumed dopaminergic neurones in the substantia nigra pars compacta and ventral tegmental area of rat brain slices. The ability of selective dopamine receptor agonists to hyperpolarize neurones and inhibit cell firing, as well as the ability of dopamine receptor antagonists to block responses to quinpirole were compared.
Six dopamine receptor agonists were examined for their ability to hyperpolarize neurones within the substantia nigra pars compacta. Of these, the most potent ligand tested was naxagolide with an EC50 value of 20 nm and estimated maximum of 10 mV. The rank order of agonist potency was naxagolide> quinpirole>apomorphine>dopamine.
Quinpirole was more potent at inhibiting cell firing in the substantia nigra pars compacta (pIC50 = 7.65 ± 0.06, n = 35) than in the ventral tegmental area (pIC50 = 7.24 ± 0.06, n = 32; P < 0.01, Student's t test). 7‐Hydroxy‐N,N‐di‐n‐propyl‐2‐aminotetralin (7‐OH‐DPAT), a putative D3 selective agonist, had a comparable potency to quinpirole in both the ventral tegmental area (pIC50 = 7.39 ± 0.26, n = 4), and substantia nigra pars compacta (pIC50 = 7.71 ± 0.20; n = 4).
The inhibition of cell firing by quinpirole was antagonized by haloperidol, S(−)−sulpiride, clozapine, and ritanserin. S(−)‐sulpiride and haloperidol had the highest estimated affinities in the substantia nigra, with pA2 values of 8.97 (slope = 0.85) and 8.20 (slope = 2.09) respectively. The pA2 values for S(−)‐sulpiride and haloperidol in the ventral tegmental area were 8.07 (slope =0.87) and 8.11 (slope= 1.48) respectively. Clozapine had a lower functional affinity than S(−)‐sulpiride and haloperidol in both the substantia nigra (pA2 = 6.47, slope = 1.19) and ventral tegmental area (pA2 = 6.53, slope 0.87). Ritanserin, a 5‐HT2 receptor antagonist that also binds to D2‐like dopamine receptors, caused a slight but significant shift in the concentration‐effect curve to quinpirole with an estimated pKA of 6.97 ± 0.13 (n = 4) in the substantia nigra and pKA of 7.12 ± 0.22 (n = 4) in the ventral tegmental area.
Comparison of these data with the binding affinity for cloned dopamine receptors demonstrates that the responses to quinpirole on dopaminergic neurones in both the A9 (substantia nigra) and A10 (ventral tegmental area) brain areas are consistent with the activation of predominantly D2, and not D3 or D4 dopamine receptors. Furthermore, the similarity in functional affinity of antagonists for these receptors suggest that the mesolimbic selectivity of atypical neuroleptics, like clozapine, may be a consequence of their actions on other receptors or their effects elsewhere in the brain.
The influence of acetazolamide and amlodipine on the intracellular sodium content of rat proximal tubular cells
Authors: Wong Patrick S.K. , Barclay Paul L. , Newman Michael J. , Johns Edward J. 
Published: July 2012

This investigation set out to use 23Na n.m.r. spectroscopy to measure changes in intracellular levels of sodium in isolated suspensions of rat proximal tubules. The effects of temperature, an inhibitor of the sodium pump and known natriuretic drugs on intracellular sodium content of such tubular preparations were measured and compared with calcium channel antagonists where action at this level is unclear.
Rat kidneys were perfused with collagenase, roughly chopped, subjected to mechanical dispersion and washed to remove all traces of the enzyme. The proximal tubules were then purified and concentrated by Percoll density gradient centrifugation and then resuspended in buffer containing dysprosium tripolyphosphate shift reagent.
Distinct peaks corresponding to intracellular and extracellular sodium signals were observed when the tubules were placed into the n.m.r. spectrometer. As the temperature of the suspension rose to 37°C, there was an exponential decrease in sodium content, with a decay constant of 0.15 ± 0.02 min−1, which reached a stable level within 20 to 25 min. Addition of ouabain, 10−3 m, resulted in a significant (P < 0.01) 30% increase in intracellular sodium content within 5 min which peaked at 70% 20 min later. Although acetazolamide (10−3 m) significantly (P < 0.01) increased intracellular sodium content by 45%, amlodipine (10−4m) had no effect.
These data show that changes in the activity of the Na+/K+/ATPase have a considerable influence on the intracellular levels of sodium in proximal tubule cells. Inhibition of carbonic anhydrase activity resulted in a rise in intracellular sodium content which is compatible with its action to reduce the turnover rate of the Na+/(HCO3−)3 symporter. The lack of effect of amlodipine was consistent with the suggestion that it does not have a direct action on the sodium handling processes at the level of the proximal tubule.
Effects of selective ETB‐receptor stimulation on arterial, venous and capillary functions in cat skeletal muscle
Authors: Ekelund Ulf , Adner Mikael , Edvinsson Lars , Mellander Stefan 
Published: July 2012

This paper describes, in quantitative terms, the in vivo effects of two selective ETB‐receptor agonists (IRL 1620 and BQ 3020) on vascular resistance (tone) in the following consecutive sections of the vascular bed of sympathectomized cat skeletal muscle: large‐bore arterial resistance vessels (> 25 μm), small arterioles (< 25 μm) and the veins. The effects on capillary pressure and transcapillary fluid exchange were also recorded.
Both IRL 1620 and BQ 3020, infused i.a. to the muscle preparation, evoked an initial transient dilator response followed by a moderate dose‐dependent constrictor response, both being preferentially confined to the small arterioles. The dilator response was associated with a transient increase, and the constrictor response with a sustained decrease, in capillary pressure, the latter causing net transcapillary fluid absorption. The capillary filtration coefficient decreased during the constrictor response, indicating constriction of terminal arterioles/precapillary sphincters.
The vascular responses to the ETB‐receptor agonists were unaffected by blockade of endothelium‐derived nitric oxide (NG‐nitro‐l‐arginine methyl ester) and by selective ETA‐receptor blockade (FR139317). However, blockade of prostacyclin production with indomethacin decreased the amplitude of the dilator response, and decreased the time required to reach a steady‐state vasoconstrictor response to the ETB‐receptor agonists.
The effect of ETB‐receptor stimulation on vascular tone was also evaluated in vitro on the cat femoral artery and vein. IRL 1620 had no effect on the femoral artery but caused a weak dose‐dependent relaxation in the femoral vein. This large vein relaxation response seemed to be mediated by endothelium‐derived nitric oxide and not by prostacyclin.
It may be concluded that ETB‐receptor stimulation is responsible for the dilator response, and can contribute to the constrictor response, elicited by endothelins in cat skeletal muscle in vivo.
Endothelin‐1‐induced myocardial ischaemia and oedema in the rat: involvement of the ETA receptor, platelet‐activating factor and thromboxane A2
Authors: Filep János G. , Fournier Alain , Földes‐Filep Éva 
Published: July 2012

The objectives of the present experiments were to assess the role of ETA receptors in mediating endothelin‐1 (ET‐1)‐induced myocardial ischaemia and oedema and to study the involvement of platelet‐activating factor (PAF) and thromboxane A2 (TxA2) in these actions of ET‐1 in rats.
Intravenous bolus injection of ET‐1 (0.1–2 nmol kg−1) into anaesthetized rats induced ST segment elevation of the electrocardiogram in a dose‐dependent manner without causing arrhythmias. ST segment elevation developed within 20–90 s and persisted for at least 10–20 min following administration of ET‐1.
Pretreatment of the animals with the selective endothelin ETA receptor antagonist, FR 139317 (2.5 mg kg−1, i.v.) inhibited by 86% the ST segment elevation elicited by ET‐1 (1 nmol kg−1). Pretreatment with intravenous administration of BM 13505 (1 mg kg−1), a TxA2 receptor antagonist, OKY‐046 (10 mg kg−1), a thromboxane synthase inhibitor or the specific PAF receptor antagonist, WEB 2086 (1 mg kg−1) or BN 52021 (10 mg kg−1) markedly suppressed ST segment elevation in response to ET‐1. Infusion of indomethacin (3 mg kg−1 bolus plus 2 mg kg−1 h−1) did not significantly affect ET‐1‐induced ST segment elevation.
Bolus injection of ET‐1 (1 nmol kg−1, i.v.) to conscious rats resulted in a prolonged pressor effect preceded by a transient depressor response. Corresponding to changes in blood pressure, a small transient tachycardia was followed by a sustained bradycardia. ET‐1 enhanced albumin leakage by 87 and 120% in the left ventricle and right atrium, respectively, as measured by the extravasation of Evans blue dye.
The selective ETA receptor antagonist, FR 139317 (2.5 mg kg−1) significantly blunted the pressor action of ET‐1 and the accompanying bradycardia without affecting the depressor response. Furthermore, FR 139317 almost completely abolished the permeability effect of ET‐1 in both vascular beds studied.
Pretreatment of the animals with BM 13505 (1 mg kg−1), OKY‐046 (10 mg kg−1), WEB 2086 (1 mg kg−1) or BN 52021 (10 mg kg−1) significantly reduced ET‐1 (1 nmol kg−1)‐induced albumin extravasation both in the left ventricle and right atrium. The PAF receptor antagonists, WEB 2086 and BN 52021 were equally potent inhibitors in the left ventricle, whereas BN 52021 appeared to be a more potent inhibitor than WEB 2086 in the right atrium. Pretreatment with indomethacin (3 mg kg−1 plus 2 mg kg−1 h−1) did not modify the permeability response to ET‐1. None of these compounds affected significantly ET‐1‐induced changes in mean arterial blood pressure and heart rate.
These results indicate that intravenous administration of ET‐1 provokes ST segment elevation and myocardial oedema and suggest that these events are mediated, in part, through release of secondary mediators, such as PAF and TxA2 via the activation of ETA receptors.
Action of niflumic acid on evoked and spontaneous calcium‐activated chloride and potassium currents in smooth muscle cells from rabbit portal vein
Authors: Hogg R.C. , Wang Q. , Large W.A. 
Published: July 2012

The action of niflumic acid was studied on spontaneous and evoked calcium‐activated chloride (ICl(Ca)) and potassium (IK(Ca)) currents in rabbit isolated portal vein cells.
With the nystatin perforated patch technique in potassium‐containing solutions at a holding potential of – 77 mV (the potassium equilibrium potential), niflumic acid produced a concentration‐dependent inhibition of spontaneous transient inward current (STIC, calcium‐activated chloride current) amplitude. The concentration to reduce the STIC amplitude by 50% (IC50) was 3.6 × 10−6 m.
At – 77 mV holding potential, niflumic acid converted the STIC decay from a single exponential to 2 exponential components. In niflumic acid the fast component of decay was faster, and the slow component was slower than the control decay time constant. Increasing the concentration of niflumic acid enhanced the decay rate of the fast component and reduced the decay rate of the slow component.
The effect of niflumic acid on STIC amplitude was voltage‐dependent and at – 50 and + 50 mV the IC50 values were 2.3 × 10−6 m and 1.1 × 10−6 m respectively (cf. 3.6 × 10−6 m at −77 mV).
In K‐free solutions at potentials of – 50 mV and + 50 mV, niflumic acid did not induce a dual exponential STIC decay but just increased the decay time constant at both potentials in a concentration‐dependent manner.
Niflumic acid, in concentrations up to 5 × 10−5 m, had no effect on spontaneous calcium‐activated potassium currents.
Niflumic acid inhibited noradrenaline‐ and caffeine‐evoked ICl(Ca) with an IC50 of 6.6 × 10−6 m, i.e. was less potent against evoked currents compared to spontaneous currents. In contrast niflumic acid (2 × 10−6 m–5 × 10−5 m) increased noradrenaline‐ and caffeine‐induced IK(Ca).
The results are discussed with respect to the mechanism of block of ICl(Ca) by niflumic acid and its suitability as a pharmacological tool for assessing the role of ICl(Ca) in physiological mechanisms.
The effects of chronic imidazoline drug treatment on glial fibrillary acidic protein concentrations in rat brain
Authors: Olmos Gabriel , Alemany Regina , Escriba Pablo V. , García‐Sevilla Jesús A. 
Published: July 2012

The concentration of the astrocytic marker, glial fibrillary acidic protein (GFAP) was quantitated by immunoblotting (western blotting) in the rat brain after treatment with various imidazoline drugs and other agents.
Chronic (7 days) but not acute (1 day) treatment with the imidazoline drugs, cirazoline (1 mg kg−1, i.p.) and idazoxan (10 mg kg−1, i.p.), but not with the structurally related α2‐adrenoceptor antagonists, RX821002 (2‐methoxy idazoxan) (10 mg kg−1, i.p.) and efaroxan (10 mg kg−1, i.p.), markedly increased (45%) GFAP immunoreactivity in the rat cerebral cortex. Chronic treatment (7 days) with yohimbine (10 mg kg−1, i.p.), a non‐imidazoline α2‐adrenoceptor antagonist, did not significantly modify GFAP immunoreactivity in the cerebral cortex.
Chronic treatment (7 days) with cirazoline and idazoxan did not alter the density of brain monoamine oxidase (MAO)‐B sites labelled by [3H]‐Ro 19–6327 (lazabemide), another relevant astroglial marker. Moreover, these imidazoline drug treatments did not modify the levels of α‐tubulin in the cerebral cortex. These negative results reinforced the specificity of the effects of imidazoline drugs on GFAP.
Irreversible inactivation of brain α2‐adrenoceptors (and other neurotransmitters receptors) after treatment with an optimal dose of the peptide‐coupling agent EEDQ (1.6 mg kg−1, i.p., for 6–24 h) did not alter GFAP immunoreactivity in the cerebral cortex. These results further disproved the involvement of these receptors on astroglial cells in the tonic control of GFAP levels.
The binding of [3H]‐idazoxan in the presence of 10−6 m (–)‐adrenaline was used to quantitate in parallel I2‐imidazoline preferring sites in the rat brain after the same treatments. Chronic treatment (7 days) with cirazoline and idazoxan, but not with RX821002, efaroxan or yohimbine, significantly increased (25%) the density of I2‐sites in the cerebral cortex. The up‐regulation of I2‐sites induced by cirazoline was not observed in the liver, a tissue that also expresses I2‐sites but lacks glial cells.
A strong correlation (r = 0.97) was found when the mean percentage changes in GFAP immunoreactivity were related to the mean percentage changes in I2 imidazoline sites after the various drug treatments.
Together the results suggest a direct physiological function of glial I2‐imidazoline preferring sites in the regulation of GFAP levels.
Routes of delivery of muscarinic acetylcholine receptors to the plasma membrane in NG108‐15 cells
Authors: Koenig Jennifer A. , Edwardson J. Michael 
Published: July 2012

We have examined the routes of delivery of muscarinic acetylcholine receptors to the plasma membrane in unstimulated and agonist‐stimulated NG108‐15 cells. Delivery of receptors to the plasma membrane was measured by irreversibly alkylating receptors already at the cell surface with propyl‐<***>benzilylcholine mustard (PrBCM) and then following the recovery of binding of the polar radioligand [3H]‐N‐methylscopolamine ([3H]‐NMS) in intact cells.
In unstimulated cells, recovery of [3H]‐NMS binding after 2 h of incubation at 37°C was 30% of binding in control cells. Binding affinity of [3H]‐NMS was unchanged. In cells that had been pre‐exposed to carbachol (0.5 mm) for 30 min, initial [3H]‐NMS binding was reduced by 38% but recovery of binding was increased from 30% to 43% of control binding.
When the cells were pre‐incubated for 1 h with the protein synthesis inhibitor cycloheximide (20 μg ml−1), recovery of [3H]‐NMS binding was reduced by similar extents in unstimulated (30% to 9%) and carbachol‐stimulated (43% to 19%) cells. Incubation of the cells at 20°C instead of 37°C reduced recovery of [3H]‐NMS binding from 30% to 9% in unstimulated cells and from 43% to 23% in carbachol‐stimulated cells.
Depletion of cellular ATP by addition of antimycin (50 nm) and deoxyglucose (50 mm), reduced recovery of binding to 12% in unstimulated cells and to 6% in carbachol‐stimulated cells.
These results indicate that in unstimulated NG108‐15 cells, delivery of muscarinic receptors to the plasma membrane is almost exclusively through the synthetic pathway. In agonist‐stimulated cells, receptor sequestration into an intracellular compartment (probably endosomes) occurs. Under these circumstances, delivery of receptors to the plasma membrane along the synthetic route is unaffected but an additional route of delivery (recycling) now operates.
Induction of kinin B1 receptor‐dependent vasoconstriction following balloon catheter injury to the rabbit carotid artery
Authors: Pruneau D. , Luccarini J.M. , Robert C. , Bélichard P. 
Published: July 2012

Balloon catheter injury to the rabbit carotid artery damaged the endothelium and induced neointima formation over 7 days. The area of intima, expressed as a percentage of the media, was 16.2 ± 4.2% and 8.2 ± 0.1% in balloon catheter‐injured and sham‐operated arteries.
Seven days after arterial injury, carotid arteries were isolated and set up as ring preparations in organ baths for isometric tension measurements. Balloon catheter‐injured arteries first contracted with noradrenaline (0.01–0.1 μm), contracted further in a concentration‐dependent manner to bradykinin (BK; pD2, 5.98 ± 0.22; Emax, 41.3 ± 5.2% of KCl) and to des‐Arg9‐BK (pD2, 7.12 ± 0.36; Emax, 46.0 ± 9.9% of KCl). In contrast, vessel segments with endothelium either intact or acutely removed were unresponsive to both BK receptor agonists.
The concentration‐contraction curves for BK and for des‐Arg9‐BK were shifted to the right by the B1 receptor antagonist, [Leu8]des‐Arg9‐BK (3 μm), but not by the selective B2 receptor antagonist, Hoe 140 (1 μm).
Thus, BK and its metabolite, des‐Arg9‐BK act as vasoconstrictor agents following balloon catheter injury. These effects appear to be mediated by activation of B1 receptors.
Stimulation of phospholipase C in cultured microvascular endothelial cells from human frontal lobe by histamine, endothelin and purinoceptor agonists
Authors: Purkiss John R. , West David , Wilkes Leslie C. , Scott Caroline , Yarrow Peter , Wilkinson Graeme F. , Boarder Michael R. 
Published: July 2012

Cultures of endothelial cells derived from the microvasculature of human frontal lobe have been investigated for phospholipase C (PLC) responses to histamine, endothelins and purinoceptor agonists.
Using cells prelabelled with [3H]‐inositol and measuring total [3H]‐inositol (poly)phosphates, histamine acting at H1 receptors stimulated a substantial response with an EC50 of about 10 μm.
Endothelin‐1 also gave a clear stimulation of phosphoinositide‐specific phospholipase C. Both concentration‐response curves and binding curves showed effective responses and binding in the rank order of endothelin‐1>sarafotoxin S6b>endothelin‐3, suggesting an ETA receptor.
Assay of total [3H]‐inositol (poly)phosphates showed no response to the purinoceptor agonists, 2‐methylthioadenosine 5′‐trisphosphate (2MeSATP), adenosine 5′‐O‐(3‐thiotrisphosphate) (ATPγS) or β,γ‐methylene ATP. Both ATP and UTP gave a small PLC response.
Similarly, when formation of [32P]‐phosphatidic acid from cells prelabelled with 32Pi was used as an index of both PLC and phospholipase D, a small response to ATP and UTP was seen but there was no response to the other purinoceptor agonists tested.
Study by mass assay of stimulation by ATP of inositol (1,4,5) trisphosphate accumulation revealed a transient response in the first few seconds, a decline to basal, followed by a small sustained response.
These results show that human brain endothelial cells in culture are responsive to histamine and endothelins in a manner which may regulate brain capillary permeability. Purines exert a lesser influence.
Effect of subthreshold ouabain on the tone of guinea‐pig aortic strips following repeated noradrenaline stimulation
Authors: Bova Sergio , Rossi GianPaolo , Luciani Sisto , Debetto Patrizia , Pessina Achille C. , Cargnelli Gabriella 
Published: July 2012

The effect of ouabain at a concentration (0.8 μm) that does not induce contractile response in guinea‐pig aortic strips has been studied on endothelium‐denuded strips repeatedly stimulated with 1 μm noradrenaline or 60 mm K+applied for 5 min every 30 min.
The resting tone (i.e. the tone between one noradrenaline stimulation and the following) of the aortic strips exposed to ouabain increased progressively, whereas the control strips (no ouabain) completely relaxed on washout of the agonist. In the aortic strips stimulated by 60 mm K+, the resting tone did not increase.
The calcium antagonist, verapamil, did not affect the increase in tone, that was nevertheless strictly dependent on external calcium, since the contracted strips completely relaxed on calcium removal and promptly contracted again on calcium readdition. This finding indicates a mechanism independent of voltage‐gated calcium channels.
Caffeine‐induced contractions, taken as a measure of sarcoplasmic reticulum calcium content, were amplified by the presence of ouabain in aortic strips either stimulated by noradrenaline or unstimulated, with a larger increase in the former.
These results suggest that the repeated stimulation of guinea‐pig aortic strips by noradrenaline in the presence of ouabain, by raising both intracellular Na+and Ca2+, decreases the ouabain threshold concentration required for contraction, thus increasing the responsiveness of vascular smooth muscle to the glycoside.
Effect of the putative cognitive enhancer, linopirdine (DuP 996), on quantal parameters of acetylcholine release at the frog neuromuscular junction
Authors: Provan Spencer D. , Miyamoto Michael D. 
Published: July 2012

The subcellular mechanism and site of action of linopirdine or DuP 996 (3,3‐bis(4‐pyridinylmethyl)‐1‐phenylindolin‐2‐one) was investigated at the frog neuromuscular junction, using miniature endplate potential (m.e.p.p.) counts and a new method for obtaining unbiased estimates of n (number of functional release sites), p (probability of release), and varsp (spatial variance in p).
DuP 996 produced an increase in m (no. of quanta released), which was due to an increase in n and p. The increase in m was concentration‐dependent over a range of 0.1–100 μm and completely reversible with 15 min of wash. There was a saturation in the increase in p, but not in the increase in m and n, for [DuP 996] >10 μm. By contrast, there was no major change in varsp.
Block of presynaptic Na+‐ and Ca2+‐channels with 3 μm tetrodotoxin and 1.8 mm Co2+prevented the m.e.p.p. frequency increase to DuP 996, and this effect was completely reversed by washing.
Application of the neuronal Ca2+‐channel blocker, ω‐conotoxin GVIA (1 μm) brought about a rapid and profound decrease in the m.e.p.p. frequency increase produced by DuP 996. The effect of the toxin was not reversed by prolonged washing.
Block of voltage‐gated K+‐channels with 100 μm 4‐aminopyridine (4‐AP) resulted in only a small (28%) increase in m. The combination of 4‐AP (100 μm) and DuP 996 (10 μm) produced an increase in m (189%) which was much greater than the sum of the responses to each agent alone. This increase in m was due solely to an increase in n, as p and varsp were unchanged.
For [DuP 996] up to 100 μm, there was no apparent change in the mean size, amplitude distribution, or time course of m.e.p.ps, signifying that it had no anticholinesterase activity.
It is concluded that DuP 996 increases the release of quantal transmitter but not the postsynaptic response to the quanta. This appears to involve an effect at the nerve terminal membrane, most likely an increase in Ca2+‐conductance, and not an action to block K+‐conductance or to release Ca2+from intraterminal organelles.