bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of NMDA effects on agonist‐stimulated phosphoinositide turnover by memantine in neonatal rat cerebral cortex
Authors: Mistry Rajendra , Wilke Rolf , Challiss R.A. John 
Published: July 2012

The ability of memantine (1‐amino‐3,5‐dimethyladamantane) to antagonize the modulatory effects of N‐methyl‐d‐aspartate (NMDA) on phosphoinositide turnover stimulated by muscarinic cholinoceptor‐and metabotropic glutamate receptor‐agonists has been examined in neonatal rat cerebral cortex slices.
Memantine antagonized the inhibitory effect of NMDA (100 μm) on both total [3H]‐inositol phosphate ([3H]‐InsPx) and inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) mass accumulations stimulated by carbachol (1 mm) with EC50 values of 21 and 16 μm respectively.
Memantine concentration‐dependently antagonized (IC50 24 μm) the ability of NMDA (10 μm) to potentiate [3H]‐InsPx accumulation in response to a sub‐maximal concentration of the metabotropic glutamate receptor agonist, 1S,3R‐ACPD (10 μm).
The small (approx. 3 fold), concentration‐dependent increase in [3H]‐InsPx accumulation stimulated by NMDA was completely antagonized by the prototypic NDMA receptor‐channel blocker, MK‐801 (1 μm) at all concentrations of NDMA studied (1 – 1000 μm). In contrast, antagonism by memantine (100 μm) was observed only at low concentrations of NMDA (1 – 10 μm), whilst [3H]‐InsPx accumulation stimulated by high concentrations of NMDA (300 – 1000 μm) was markedly enhanced by memantine.
Assessment of the incorporation of [3H]‐inositol into inositol phospholipids revealed that memantine (100 μm) caused an approximate 2 fold increase in the labelling of phosphatidylinositol, phos‐phatidylinositol 4‐phosphate and phosphatidylinositol 4,5‐bisphosphate.
H.p.l.c. separation of [3H]‐inositol (poly)phosphates demonstrated that whilst memantine (100 μm) alone had no significant effect on the accumulation of any isomer, it substantially altered the profile of accumulation stimulated by NMDA (1 mm), greatly facilitating accumulation of Ins(1,4,5)P3 and inositol 1,3,4,5‐tetrakisphosphate (Ins(1,3,4,5)P4).
These data provide evidence that memantine can antagonize the actions of NMDA in neonatal rat cerebral cortex slices in a manner consistent with this agent acting as a NMDA receptor‐channel blocker. In addition, at least two further actions of memantine can be proposed. Memantine increases the rate of [3H]‐inositol incorporation into the cellular inositol phospholipid fraction, without significantly stimulating phosphoinositide turnover. Furthermore, memantine can substantially alter patterns of inositol (poly)phosphates stimulated by NMDA, promoting the accumulation of the established and putative second messengers Ins(1,4,5)P3 and Ins(1,3,4,5)P4 which are not increased by NMDA in the absence of memantine. It is unknown whether these latter loci of memantine action contribute to known therapeutic actions of this agent.
Rapid degradation of endothelin‐1 by an enzyme released by the rat isolated perfused mesentery
Authors: Pérez‐Vizcaíno Francisco , Cooper Andrea C. , Corder Roger , Fournier Alain , Warner Timothy D. 
Published: July 2012

In vivo the effects of endothelin‐1 (ET‐1) are limited by its rapid removal from the circulation and possibly by its metabolism by enzymes such as neutral endopeptidase 24.11, deamidase or carboxypeptidase A. Here, using as a model the isolated perfused mesenteric arterial bed of the rat, we have examined the involvements of these enzymatic activities in the vascular responses to ET‐1.
Samples of Krebs buffer which had been recirculated through the mesenteric arterial bed for 30 min rapidly destroyed the activity of ET‐1 as assessed either by bioassay on rings of rat thoracic aorta or by high performance liquid chromatography (h.p.l.c). For instance, after 15 min incubation with the recirculated‐Krebs solution (recirc‐K) the contraction induced by 3 times 10−9 m ET‐1 was reduced by more than 90%. Contractions induced by sarafotoxin 6b (3 times 10−9 m) were similarly suppressed by preincubation with recirc‐K whereas those to Arg‐vasopressin (3 times 10−9 m) were unaffected.
The degradation of ET‐1 by recirc‐K was prevented by 1,10‐phenanthroline (10−3 m), abolished by heating the recirc‐K solution to 90°C for 15 min, and reduced by EGTA (5 times 10−3 m) or ET‐1(16–21) (10−5 m). For instance, in the presence of ET‐1(16–21) (n = 6) the contraction induced by ET‐1 was reduced by only 40% after 15 min incubation with recirc‐K buffer. Leupeptin (3 times 10−4 m), dichloroisocoumarin (5 times 10−5 m), phenylmethyl‐sulphonyl fluoride (10−3 m), a combination of bacitracin (300 mg ml−1), bestatin (10−5 m), captopril (10−5 m), phosphoramidon (10−4 m) and thiorphan (10−4 m) or Polypep (a proprietary protein digest) did not inhibit the degradation of ET‐1 by recirc‐K.
In experiments examining directly the vascular responses of the isolated perfused mesentery of the rat, the addition of cumulative concentrations of ET‐1 to the recirculating Krebs solution caused small concentration‐dependent increases in perfusion pressure. The inclusion of ET‐1(16–21), ET‐1(17–21), or ET‐1(18–21) (10−5 m) greatly potentiated these responses, but not those to Arg‐vasopressin or methoxamine. The effects of 1, 10‐phenanthroline or EGTA could not be examined in this system because these agents both depressed non‐specifically the vasoconstrictor responses of the mesenteric vascular bed.
Thus, the rat mesentery releases an enzyme that very rapidly destroys ET‐1 or the very closely related peptide, sarafotoxin 6b but not Arg‐vasopressin. This enzyme is most probably a metallo‐peptidase because of its sensitivity to inhibition by 1,10‐phenanthroline or EGTA. It is particularly interesting that a simple vascular bed such as the mesentery produces such a powerful endothelin metabolising enzyme. It is tempting, therefore, to speculate that the endothelin degrading enzyme active at neutral pH that we have found is important in the metabolism of ET‐1 throughout the vasculature.
P2‐purinoceptor‐mediated inhibition of noradrenaline release in rat atria
Authors: von Kügelgen Ivar , Stoffel Daniel , Starke Klaus 
Published: July 2012

We looked for P2‐purinoceptors modulating noradrenaline release in rat heart atria. Segments of the atria were preincubated with [3H]‐noradrenaline and then superfused with medium containing desipramine (1 μm) and yohimbine (1 μm) and stimulated electrically, by 30 pulses/I Hz unless stated otherwise.
The adenosine Al‐receptor agonist, N6‐cyclopentyl‐adenosine (CPA; EC50 9.7 nM) and the nucleotides, ATP (EC50 6.6 μm) and adenosine‐5′‐O‐(3‐thiotriphosphate) (ATPγS; EC50 4.8 μm), decreased the evoked overflow of tritium. The adenosine A2a‐agonist, 2‐p‐(2‐carbonylethyl)‐phenethylamino‐5′‐N‐ethylcarboxamido‐adenosine (CGS‐21680; 0.03‐0.3 μm) and the P2X‐purinoceptor agonist β,γ,‐methylene‐l‐ATP (30 μm) caused no change.
The concentration‐response curve of CPA was shifted to the right by the adenosine Al‐receptor antagonist, 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX; 3 nM; apparent pKB value 9.7) but hardly affected by the P2‐purinoceptor antagonist, cibacron blue 3GA (30 μm). In contrast, the concentration‐response curves of ATP and ATPγS were shifted to the right by DPCPX (3 nM; apparent pKB values 9.3 and 9.4, respectively) as well as by cibacron blue 3GA (30 μm; apparent pKB values 5.0 and 5.1, respectively). Combined administration of DPCPX and cibacron blue 3GA caused a much greater shift of the concentration‐response curve of ATP than either antagonist alone. The concentration‐response curve of ATP was not changed by indomethacin, atropine or the 5′‐nucleotidase blocker α,β‐methylene‐ADP.
Cibacron blue 3GA (30 μm) increased the evoked overflow of tritium by about 70%. The increase was smaller when the slices were stimulated by 9 pulses/100 Hz instead of 30 pulses/I Hz.
The results indicate that the postganglionic sympathetic axons in rat atria possess P2‐purinoceptors in addition to the known adenosine Al‐receptor. Both mediate inhibition of noradrenaline release. Some adenine nucleotides such as ATP and ATPγS act at both receptors. The presynaptic P2‐purinoceptor seems to be activated by an endogenous ligand, presumably ATP, under the condition of these experiments. This is the first evidence for presynaptic P2‐purinoceptors at cardiac postganglionic sympathetic axons.
Subcellular localization and molecular pharmacology of distinct populations of [3H]‐AMPA binding sites in rat hippocampus
Authors: Henley Jeremy M. 
Published: July 2012

The subcellular distributions of [3H]‐α‐amino‐3‐hydroxy‐5‐methylisoxazolepropionate ([3H]‐AMPA) and [3H]‐kainate binding sites in rat hippocampus were investigated by cell fractionation techniques.
Two major populations of [3H]‐AMPA sites were detected with the majority of binding located intracellularly in the microsomal (P3) fraction. Most of the remaining sites were in the synaptosomal membrane fraction but some were also present in the nuclear fraction. In contrast, essentially all of the [3H]‐kainate binding sites were in the synaptosomal membrane fraction.
Saturation binding analysis yielded KD and Bmax values for [3H]‐AMPA of 147 nM and 2.6 pmol mg−1 protein respectively for the synaptosomal membrane‐associated sites and 129 nM and 5.3 pmol mg−1 protein respectively for the microsomal sites.
Both main populations of [3H]‐AMPA sites displayed the same rank order of inhibition by competitive ligands, the apparent Mr values of GluR1 subunits were equivalent, suggesting the same degree of post‐translational modification and the hydrodynamic properties of the receptor complexes were identical.
These data are consistent with the hypothesis that the movement of AMPA receptors between cellular compartments in the postsynaptic neurone could constitute one mechanism underlying long‐term potentiation in the hippocampus.
Modulatory effect of bradykinin on the release of noradrenaline from rat isolated atria
Authors: Chulak Chantal , Couture Réjean , Foucart Sylvain 
Published: July 2012

We investigated the modulation by bradykinin (BK) of electrically induced noradrenaline release in rat isolated atria preincubated with [3H]‐noradrenaline.
BK (1‐100nM) enhanced significantly the stimulation‐induced outflow of radioactivity in a concentration‐dependent manner with a calculated EC50 of 0.58 nM.
Des‐Arg9‐BK (0.1‐100nM), a selective B1 receptor agonist, did not modify the stimulation‐induced outflow of radioactivity. Hoe 140 (10 nM), a selective B2 receptor antagonist, but not [Leu8]‐des‐Arg9‐BK (100 nM), a selective B1 receptor antagonist, blocked the facilitatory effect of BK.
The effect of BK was not affected by diclofenac (1 μm), a cyclo‐oxygenase inhibitor. Bisindolyl‐maleimide (1 μm), a protein kinase C inhibitor, significantly reduced the facilitatory effect of BK (10 nM), angiotensin II (0.3 μm) and phorbol dibutyrate (0.1 and 1 μm) but not of fenoterol (1 μm).
The results suggest that BK enhances noradrenaline release via a prejunctional B2 kinin receptor in the rat atrium. The effect appears to involve protein kinase C as a second messenger.
Renal vasodilatation by dopexamine and fenoldopam due to α1‐adrenoceptor blockade
Authors: Martin S.W. , Broadley K.J. 
Published: July 2012

The renal vascular responses of the rat isolated perfused kidney to the dopamine D,‐receptor agonists, dopexamine and fenoldopam, were examined.
Both kidneys were perfused in situ at constant flow rate (11ml min−1) with Krebs‐bicarbonate solution at 37°C. The perfusion pressure was monitored and to enable vasodilator responses to be measured, the resting perfusion pressure was raised by infusing noradrenaline (6 × 10−9 m).
Dose‐related vasodilator responses to bolus doses of dopexamine and fenoldopam were obtained. However, these were not antagonized by the D1‐receptor antagonist, SCH 23390, indicating that D1‐receptors were not involved.
Bolus doses of the α1‐adrenoceptor antagonist, prazosin, caused similar dose‐related vasodilator responses indicating the possibility that α1‐adrenoceptor blocking properties of dopexamine and fenoldopam were responsible for the vasodilatation.
α‐Adrenoceptor blockade by dopexamine and fenoldopam was confirmed by the parallel displacement of dose‐response curves for the vasopressor responses to noradrenaline. pA2 values were determined by Schild analysis for dopexamine, fenoldopam and prazosin antagonism of noradrenaline in the presence of neuronal (cocaine, 10−5 m) and extraneuronal uptake blockade (metanephrine, 10−5 m). The values were 6.23, 6.02 and 8.91, respectively. Schild plot slopes of unity were obtained for dopexamine and fenoldopam indicating competitive antagonism. A slope of greater than unity for prazosin may be explained by the lack of equilibrium conditions associated with bolus doses of noradrenaline, the responses of which are affected more by the high affinity antagonist, prazosin, than the two lower affinity antagonists.
This study has demonstrated that renal vasodilator responses to the D1‐receptor agonists, dopexamine and fenoldopam, are due to a brief antagonism of the α‐adrenoceptor‐mediated vasoconstriction induced by noradrenaline. This presumably masks any direct D1‐receptor‐mediated vasodilatation.
Stimulation of two vascular smooth muscle‐derived cell lines by angiotensin II: differential second messenger responses leading to mitogenesis
Authors: Morton Clare , Baines Richard , Masood Imran , Ng Leong , Boarder Michael R. 
Published: July 2012

We show here that angiotensin II (All) and endothelin‐l (ET‐1) stimulate [3H]‐thymidine incorporation in a smooth muscle cell line derived from aortae of spontaneously hypertensive rats (SHR), but not in cells derived from normotensive controls (WKY). We have used the differential response of the two cell lines to investigate the relationship between second messenger systems and the mitogenic response.
All produced an increase in accumulation of inositol 1,4,5‐triphosphate which was greater in the SHR‐derived cell line than in the WKY cells.
All gave an increase in cytosolic Ca2+ in each of the cell lines, with both a larger peak (15–30 s) and plateau response (2min) in the SHR cells. ET‐1 gave an enhanced response in the SHR‐derived cells with respect to the peak but not the plateau of cytosolic Ca2+.
Phospholipase D activity was studied by monitoring the formation of [3P]‐phosphatidylbutanol in 32Pi prelabelled cells. All stimulation gave a larger phospholipase D response in SHR‐derived cells, while ET‐1 gave a larger response in WKY‐derived cells.
Stimulation of SHR‐derived cells with 100 nM All for 1 h, followed by 19 h in the absence of agonist, stimulated [3H]‐thymidine incorporation over the next 4 h. When the 1 h stimulation with All was in the presence of increasing concentrations of butanol, which diverts the product of the phospholipase D pathway, there was a loss of stimulated [3H]‐thymidine incorporation which was significant at 10 mM butanol and at 30‐50mM reached a maximum loss of 40%.
Contrasting with this there was no apparent loss of ET‐1‐stimulated thymidine incorporation when butanol was present at concentrations up to 40 mM. 7 These results suggest that phospholipase D is one of several pathways in the mitogenic response of SHR‐derived vascular smooth muscle cells to All.
Effect of illuminated nifedipine, a potent antioxidant, on intestinal and vascular smooth muscles
Authors: Bauer V. , Rekalov V.V. , Juranek I. , Gergel D. , Bohov P. 
Published: July 2012

The effects of nifedipine (Nif) and its illuminated nitroso product nitrosopine (NTP) were investigated on lipid peroxidation, KC1 elevated smooth muscle tension, and ionic currents of single smooth muscle cells.
Illumination of Nif at 400–700 nm within 24–48 h changed it completely to a potent antioxidant, NTP.
Nif relaxed the KCl‐induced contractions of guinea‐pig taenia caeci and rat aorta and reduced the amplitude of the evoked inward Ca2+ current of taenia caeci cells in a concentration‐dependent manner. NTP (up to 100 μm) was ineffective in this respect. Pretreatment by NTP (10 μm) did not affect the actions of Nif.
The evidence suggests that NTP, generated by day‐light illumination from Nif, exerts antioxidant activity but is devoid of voltage‐dependent Ca2+ channel (VDC) blocking property and does not interfere with the action of Nif on the smooth muscle cell membrane VDC.
Substance P‐induced relaxation and hyperpolarization in human cerebral arteries
Authors: Petersson Jesper , Zygmunt Peter M. , Brandt Lennart , Högestätt Edward D. 
Published: July 2012

Vascular effects of substance P were studied in human isolated pial arteries removed from 14 patients undergoing cerebral cortical resection.
Substance P induced a concentration‐dependent relaxation in the presence of indomethacin. No relaxation was seen in arteries where the endothelium had been removed.
Nω–nitro‐L‐arginine (l‐NOARG, 0.3 mM) abolished the relaxation in arteries from six patients. The relaxation was only partially inhibited in the remaining eight patients, the reduction of the maximum relaxation being less than 50% in each patient.
The L‐NOARG‐resistant relaxation was abolished when the external K+ concentration was raised above 30 mM.
Substance P caused a smooth muscle hyperpolarization (in the presence of L‐NOARG and indomethacin), but only when the artery showed an L‐NOARG‐resistant relaxation.
The results indicate that nitric oxide is an important mediator of endothelium‐dependent relaxation in human cerebral arteries. Furthermore, another endothelium‐dependent pathway, causing hyperpolarization and vasodilatation, was identified in arteries from more than half the population of patients.
Labelling with [125I]‐SB 207710 of a small 5‐HT4 receptor population in piglet right atrium: functional relevance
Authors: Kaumann Alberto J. , Lynham James A. , Brown Anthony M. 
Published: July 2012

We investigated the affinity of SB 207710 for sinoatrial 5‐HT4 receptors and the density of right atrial 5‐HT4 receptors with [125I]‐SB 207710 in right atria of new‐born piglets.
SB 207710 (1–100 nM) antagonized the 5‐HT‐evoked tachycardia surmountably with a pKB of 9.8.
[125I]‐SB 207710 (5–1500 pM) labelled a small population of saturable binding sites with a pKD of 10.1 and with 5‐HT4 receptor characteristics. The density of atrial binding sites with 5‐HT4 receptor characteristics was 174 and 22 times lower respectively than those of atrial β1 and β2‐adrenoceptors, labelled with (−)−[125I]‐cyanopindolol.
We suggest that the small 5‐HT4 receptor population may in part explain why the maximal tachycardia caused by 5‐HT is smaller than that caused by catecholamines.
Characterization of an α1D‐adrenoceptor mediating the contractile response of rat aorta to noradrenaline
Authors: Kenny B.A. , Chalmers D.H. , Philpott P.C. , Naylor A.M. 
Published: July 2012

The affinities of a number of α1 ‐adrenoceptor antagonists were determined by displacement of [3H]‐prazosin binding from cloned human α1A‐adrenoceptors (previously designated cloned α1c subtype), α1B α1D and rat α1D‐adrenoceptors, stably expressed in rat‐1 fibroblasts. Functional affinity estimates for these compounds were also determined from noradrenaline‐mediated contractions of rat aorta.
BMY 7378 displayed high affinity for cloned human α1D‐adrenoceptors (pKi = 8.2 ±0.10) and was selective over α1A (pAi = 6.2 ±0.10) and α1B subtypes (6.7 ± 0.11). WB 4101, benoxathian and phentolamine displayed high affinity for α1A and α1D adrenoceptors compared to the α1B subtype. Spiperone displayed high affinity and selectivity for α1B adrenoceptors (pKi 8.8 ±0.16). 5‐Methyl‐urapidil was selective for cloned α1A adrenoceptors.
Comparative binding affinities (pKi for compounds at cloned human and rat1D adrenoceptors were almost identical (r = 0.99, slope =1.08).
Prazosin, doxazosin and 5‐methyl‐urapidil were potent, competitive antagonists of noradrenaline‐mediated contractions of rat aorta (pA2 values of 9.8, 8.8 and 7.8 respectively). The selective α1D antagonist BMY 7378 was also a potent antagonist on rat aorta (pKB = 8.3±0.1) but the interaction of this compound was not consistent with competitive antagonism at a single population of receptors.
Functional affinities for compounds determined against noradrenaline‐mediated contractions of rat aorta correlated well with binding affinities at cloned α1D‐adrenoceptors (r = 0.96), but not with α1A (r = 0.61) or α1B (r = 0.46) subtypes.
Noradrenaline‐mediated contractions of rat aorta were sensitive to the alkylating effects of chlorethylclonidine (CEC). CEC (10 μm) caused a small rightward shift in the noradrenaline concentration‐response curve. CEC at 100 μm caused a further shift and suppression of the maximum response to noradrenaline.
The results of this study suggest that noradrenaline predominantly, but not exclusively, mediates contraction of rat aorta through the activation of an α1D‐adrenoceptor.
Endothelial modulation of vasoconstrictor responses to endothelin‐1 in human placental stem villi small arteries
Authors: Sabry S. , Mondon F. , Levy M. , Ferre F. , Dinh‐Xuan A.T. 
Published: July 2012

The aim of this study was to assess the role of endothelial cells in the modulation of vasocontractile responses to endothelin‐1 (ET‐1) of human placental vasculature.
Isolated stem villi small arteries (diameter =170–250 μm) were obtained from healthy parturients who underwent caesarean surgery during the 39th week of pregnancy for cephalo‐pelvic disproportion. Isometric tension was measured in vascular rings mounted in a myograph system and challenged with ET‐1 (10−12 to 10−6m).
The vasocontractile response to ET‐1 was significantly (P< 0.0001) increased in endothelial‐denuded (active tension = 1156 ±214 mN mm−1) as compared with endothelial‐preserved vascular rings (active tension = 458 ± 48 mN mm−1). This difference was significantly (P<0.05) but only partly abolished by the NO synthase inhibitor NΩ‐nitro‐L‐arginine (l‐NOARG, 10−4 m).
In endothelial‐preserved rings submaximally precontracted with 5‐hydroxytryptamine (10−6 m), ET‐1 (10−12 to 10−9 m) induced dose‐dependent relaxation (maximum relaxation = 70 ±7%) at 10−9 m, which was followed, at higher doses (10−8 to 10−6 m), by a contraction. In contrast, no relaxation was seen in endothelial‐denuded rings. The relaxation in rings with endothelium was significantly (P< 0.001) reduced by l‐NOARG (10−4 m). Moreover, it was totally abolished by combined pretreatment with L‐NOARG (10−4 m) and the sulphonylurea glibenclamide (10−5 m).
In conclusion, endothelial cells modulate the vascular responses to ET‐1 through the release of NO and a substance acting on the ATP‐sensitive K+ channel of smooth muscle of stem villi small arteries from healthy parturients.