bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of flosequinan on ischaemia‐induced arrhythmias and on ventricular cyclic nucleotide content in the anaesthetized rat
Authors: Jones R.B. , Frodsham G. , Dickinson K. , Foster G.A. 
Published: July 2012

Flosequinan, milrinone, isoprenaline and forskolin given intravenously at similarly hypotensive doses have been evaluated in separate studies for their effect on ischaemia‐induced arrhythmias and on ventricular cyclic nucleotide content following coronary artery ligation in the pentobarbitone anaesthetized rat.
Flosequinan did not affect mortality or arrhythmias following coronary artery ligation in either study and no change in ventricular cyclic nucleotide content was observed.
Isoprenaline caused a significant increase in mortality (P < 0.05) in both studies whereas milrinone and forskolin caused a significant increase in mortality in only one of the two studies conducted. All three agents caused significant increases in cyclic AMP which were associated with increased incidence of arrhythmias.
When compared at similarly hypotensive doses, flosequinan, in contrast to milrinone, isoprenaline and forskolin, did not influence ischaemia‐induced arrhythmias or raise ventricular cyclic nucleotide levels in the anaesthetized rat.
Differential changes of adrenoceptor‐ and muscarinic receptor‐linked prostacyclin synthesis by the aorta and urinary bladder of the diabetic rat
Authors: Jeremy J.Y. , Thompson C.S. , Mikhailidis D.P. 
Published: July 2012

The effect of experimental diabetes mellitus (DM; hyperglycaemic, non‐ketototic; 2 months duration) in the rat on receptor‐linked prostacyclin (PGI2) synthesis (measured as 6‐oxo‐PGF1α by radioimmunoassay) was studied in the aorta and urinary bladder using adrenaline, angiotensin II (AII) and acetylcholine (ACh). Signal transduction systems were studied via stimulation of PGI2 synthesis with phorbol ester dibutyrate (PDBU; a protein kinase C activator [PKC]), Ca2+ ionophore A23187 (A23187) and thapsigargin (both elevate intracellular Ca2+, activating phospholipase A2 [PLA2]) and arachidonate (AA; substrate for PGI2 synthesis).
In response to adrenaline, AII and phorbol ester, aortic PGI2 release was markedly reduced (all > 75%) in diabetic rats compared to controls. EC50s of the dose‐response curves for adrenaline, AII and PDBU were also markedly increased in aortae from DM rats compared to controls. Although there was decreased output of PGI2 in response to A23187 by aortae from diabetic rats compared to controls, there was no difference in the EC50s (mean ± s.e.mean: diabetic, 2.7 ± 0.2 × 10−6 M; controls 2 ± 0.18 × 10−6 m). There were no differences in PGI2 release (or in the EC50s) in response to thapsigargin or AA between aortae from diabetic and control rats.
In the urinary bladder, there was a marked increase in PGI2 output in response to ACh and a marked decrease in EC50s for the ACh‐PGI2 dose‐response curves in diabetic rats (EC50= 5.8 ± 0.32 × 10−7 m) compared to controls (EC50 = 2.2 ± 0.15 × 10−6 m). Although there was an increase in PGI2 output in the urinary bladders from diabetic rats in response to A23187, there were no differences in the EC50s (control, 1.8 ± 0.2 × 10−6 m; diabetic, 1.1 ± 0.15 × 10−6 m). In the urinary bladders, there were no differences in PGI2 output (or the EC50s) in response to PDBU, thapsigargin or AA between diabetic or control rats.
These data indicate that: (i) reduced PGI2 synthesis coupled to adrenoceptors and AII receptors in the aortae of diabetic rats may be due to diminished PKC activity and not to changes in receptor density and/or affinity, Ca2+ stores, PLA2, cyclo‐oxygenase or PGI2 synthase; (ii) the diametrically opposite effect of DM on ACh‐stimulated PGI2 synthesis is not due to an increase in PKC activity, but possibly to an increase in muscarine receptor number and/or affinity; (iii) changes in receptor‐linked PGI2 synthesis are not ubiquitous in experimental DM and may be organ‐specific.
Analysis of the CCKB receptor antagonism of virginiamycin in guinea‐pig ileum longitudinal myenteric plexus
Authors: Corsi M. , Pojani G. , Dal Forno G. , Pietra C. , Gaviraghi G. , Trist D. 
Published: July 2012

Virginiamycin, a macrolide reported to bind selectively to CCKB/gastrin receptors has been studied in a functional test, namely cholecystokinin‐induced contraction of guinea‐pig ileum myenteric plexus (LMMP).
Virginiamycin (1–10 μm) antagonized the selective CCKB agonist cholecystokinin tetrapeptide (CCK‐4). The antagonism appeared not to be competitive as the highest concentration (10 μm) caused a reduction of its maximal effect. An apparent pA2 of 6.64 ± 0.06 (s.e.) could be estimated if this depression was ignored. The selective CCKB antagonist, L‐365,260 (0.01–0.3 μm) antagonized competitively the CCK‐4 induced contraction and a pKB of 8.60 ± 0.16 (s.e.) was estimated.
The combined dose‐ratio analysis for virginiamycin, tested at 3 and 10 μm in association with 0.03 and 0.1 μm L‐365,260, respectively, resulted in observed log dose‐ratios of 1.39 and 1.53. That was consistent with both antagonists acting on the same receptor in LMMP.
These data, represent the first evidence of the antagonism of virginiamycin in a functional assay and they support the hypothesis of homogeneity between CCKB receptors in the CNS and in peripheral tissues.
Production by R‐α‐methylhistamine of a histamine H3 receptor‐mediated decrease in basal vascular resistance in guinea‐pigs
Authors: McLeod Robbie L. , Gertner Sheldon B. , Hey John A. 
Published: July 2012

The effect of the selective histamine H3 receptor agonist, R‐α‐methylhistamine given intravenously (10–100 μg kg−1) was examined on baseline total peripheral resistance (TPR), and cardiovascular haemodynamics in bilaterally vagotomized, anaesthetized guinea‐pigs.
R‐α‐methylhistamine produced a dose‐dependent hypotension and fall in TPR at 30 and 100 μg kg−1. A decrease in heart rate (HR) was observed at a dose of 100 μg kg−1. R‐α‐methylhistamine (10–100 μg kg−1) also produced a dose‐dependent fall in rate pressure product (RPP). There was no effect on cardiac output (CO) or stroke volume (SV) at these doses.
Histamine H1 and H2 blockade in animals pretreated with a combination of chlorpheniramine (0.3 mg kg−1) and cimetidine (3.0 mg kg−1) did not alter the haemodynamic actions of R‐α‐methylhistamine (100 μg kg−1, i.v.). Pretreatment with the selective H3 antagonist, thioperamide (1 mg kg−1), completely blocked the action of R‐α‐methylhistamine on haemodynamic parameters.
To study the mechanism of action of R‐α‐methylhistamine, the vasodilator hydralazine (1 mg kg−1, i.v.) was used. Hydralazine lowered BP, TRP and RPP in guinea‐pigs pretreated with ipratropium (50 μg kg−1, i.v.). Hydralazine had no effect on HR, SV or CO.
R‐α‐methylhistamine (100 μg kg−1) did not affect the vasopressor action and increases in TPR produced by adrenaline (1 and 3 μg kg−1). On the other hand, the vasodilator hydralazine (1 mg kg−1, i.v.) inhibited the effects of adrenaline (3 μg kg−1) on TPR and RPP. The effect of both doses of adrenaline on BP were attenuated by hydralazine. Therefore, the inhibitory effects of R‐α‐methylhistamine are not mediated through a direct action on vascular smooth muscle.
In adrenalectomized guinea‐pigs, R‐α‐methylhistamine (100 μg kg−1) produced a drop in BP and HR. There was no difference between the effects of R‐α‐methylhistamine on blood pressure and heart rate in adrenalectomized and non‐adrenalectomized guinea‐pigs.
These results show that activation of peripheral H3 receptors lowers basal BP, HR and TPR, most likely by a peripheral prejunctional mechanism. The fall in BP and TPR is probably due to a decrease in noradrenaline release from sympathetic effector nerves innervating the resistance blood vessels.
K channel activation by nucleotide diphosphates and its inhibition by glibenclamide in vascular smooth muscle cells
Authors: Beech D.J. , Zhang H. , Nakao K. , Bolton T.B. 
Published: July 2012

Whole‐cell and inside‐out patch recordings were made from single smooth muscle cells that had been isolated enzymatically and mechanically from the rabbit portal vein.
In whole‐cells the inclusion in the recording pipette solution of nucleotide diphosphates (NDPs), but not tri‐ or monophosphates, induced a K‐current that developed gradually over 5 to 15 min. Intracellular 1 mm guanosine 5′‐diphosphate (GDP) induced a slowly developing outward K‐current at − 37 mV that reached a maximum on average of 72 ± 4 pA (n = 40). Half maximal effect was estimated to occur with about 0.2 mm GDP. Except for ADP, other NDPs had comparable effects. At 0.1 mm, ADP was equivalent to GDP but at higher concentration ADP was less effective. ADP induced its maximum effect at 1 mm but had almost no effect at 10 mm.
In 14% of inside‐out patches exposed to 1 mm GDP at the intracellular surface, characteristic K channel activity was observed which showed long (> 1 s) bursts of openings separated by longer closed periods. The current‐voltage relationship for the channel was linear in a 60 mm:130 mm K‐gradient and the unitary conductance was 24 pS.
Glibenclamide applied via the extracellular solution was found to be a potent inhibitor of GDP‐induced K‐current (IK(GDP)) in the whole‐cell. The Kd was 25 nm and the inhibition was fully reversible on wash‐out.
(IK(GDP)) was not evoked if Mg ions were absent from the pipette solution. In contrast the omission of extracellular Mg ions had no effect on outward or inward (IK(GDP)).
Inclusion of 1 mm ATP in the recording pipette solution reduced (IK(GDP)) and also attenuated its decline during long (25 min) recordings.
When perforated‐patch whole‐cell recording was used, metabolic poisoning with cyanide and 2‐deoxy‐d‐glucose induced a glibenclamide‐sensitive K‐current. This current was not observed when conventional whole‐cell recording was used. Possible reasons for this difference are discussed.
These K channels appear similar to ATP‐sensitive K channels but we refer to them as nucleotide diphosphate‐dependent K channels (KNDP) to emphasise what seems to be a primary role for nucleotide diphosphates in their regulation.
Activation of protein kinase C potentiates postsynaptic acetylcholine response at developing neuromuscular synapses
Authors: Fu Wen‐Mei , Lin Jiann‐Liang 
Published: July 2012

Phorbol 12‐myristate 13‐acetate (TPA, 1 μm) and phorbol 12,13‐dibutyrate (PDBu, 2 μm), activators of protein kinase C (PKC), increased the mean amplitude and decay time of the spontaneous synaptic currents of Xenopus nerve‐muscle coculture, whereas, 4α‐phorbol (2 μm) which is an inactive phorbol analogue had no effect.
Staurosporine (0.5 μm) and H‐7 (10 μm), inhibitors of PKC, inhibited the potentiation effects of TPA on the spontaneous synaptic currents.
Effects of TPA on the postsynaptic acetylcholine (ACh) sensitivity were examined by iontophoresis of ACh to the surface of embryonic muscle cells of 1‐day‐old Xenopus cultures. TPA increased both the amplitude and decay time of ACh‐induced whole‐cell currents in isolated myocytes.
TPA concentration‐dependently increased the mean open time of low‐conductance ACh channels but did not affect those of high‐conductance ACh channels. PDBu but not 4α‐phorbol exhibited similar effects to TPA. Staurosporine and H‐7 inhibited the increasing effects of TPA.
These results suggest that activation of PKC might be involved in synaptogenesis at developing neuromuscular synapses by the postsynaptic potentiation of ACh sensitivity.
Repeated administration of desipramine and a GABAB receptor antagonist, CGP 36742, discretely up‐regulates GABAB receptor binding sites in rat frontal cortex
Authors: Pratt Gerard D. , Bowery Norman G. 
Published: July 2012

GABAB receptor binding site densities within laminar regions of the rat frontal cortex were examined autoradiographically following repeated administration (21 days) of the antidepressants desipramine, paroxetine and amitriptyline in addition to the GABAB receptor antagonists, CGP 35348 and CGP 36742. β1‐Adrenoceptor autoradiography was studied in parallel with that for GABAB receptor sites.
The effects of these compounds were examined concomitantly on the GABAB receptor‐mediated inhibition of forskolin‐ and enhancement of noradrenaline‐stimulated cyclic AMP production.
GABAB receptor binding was increased by both desipramine (20 mg kg−1, p.o. and 10 mg kg−1, i.p.) and CGP 36742 (100 mg kg−1, i.p.) in the outer laminar region of the frontal cortex by around 50% above control levels. Conversely, no significant changes were mediated by paroxetine, amitriptyline, CGP 35348 or the GABAB receptor agonist, baclofen.
With the exception of paroxetine, all compounds down‐regulated the total β‐adrenoceptor population throughout frontal cortical laminae which was attributable to the β1‐adrenoceptor subtype. In contrast, the reduction in β‐adrenoceptors mediated by CGP 35348 and CGP 36742 did not occur as a consequence of reduced β1‐adrenoceptor numbers.
Protracted treatment with CGP 35348, failed to influence forskolin‐stimulated cyclic AMP production; however, a significant increase in the accumulation of cyclic AMP produced in response to forskolin was seen after treatment with CGP 36742.
Such discretely localized changes in GABAB receptor densities induced by desipramine and CGP 36742 may provide an explanation for the discrepancies reported in membrane binding studies and possibly implicate a role for GABAB receptor antagonists in antidepressant therapy.
Activation of the phospholipase C pathway by ATP is mediated exclusively through nucleotide type P2‐purinoceptors in C2C12 myotubes
Authors: Henning Robert H. , Duin Marry , den Hertog Adriaan , Nelemans Adriaan 
Published: July 2012

The presence of a nucleotide receptor and a discrete ATP‐sensitive receptor on C2C12 myotubes has been shown by electrophysiological experiments. In this study, the ATP‐sensitive receptors of C2C12 myotubes were further characterized by measuring the formation of inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) and internal Ca2+.
The nucleotides ATP and UTP caused a concentration‐dependent increase in Ins(1,4,5)P3 content with comparable time courses (EC50: ATP 33 ± 2 μm, UTP 80 ± 4 μm). ADP was less effective in increasing Ins(1,4,5)P3 content of the cells, while selective agonists for P1‐, P2X‐ and P2Y‐purinoceptors, adenosine, α,β‐methylene ATP and 2‐methylthio ATP, appeared to be ineffective.
Under Ca2+‐free conditions, the basal level of Ins(1,4,5)P3 was lower than in the presence of Ca2+, and the ATP‐ and UTP‐induced formation of Ins(1,4,5)P3 was diminished.
The Ins(1,4,5)P3 formation induced by optimal ATP and UTP concentrations was not additive. ATP‐ and UTP‐induced Ins(1,4,5)P3 formation showed cross‐desensitization, whereas cross‐desensitization was absent in responses elicited by one of the nucleotides and bradykinin.
The change in Ins(1,4,5)P3 content induced by effective nucleotides was inhibited by suramin. Schild plots for suramin inhibition of Ins(1,4,5)P3 formation in ATP‐ and UTP‐stimulated myotubes showed slopes greater than unity (1.63 ± 0.09 and 1.37 ± 0.11, respectively). Apparent pA2 values were 4.50 ± 0.48 and 4.41 ± 0.63 for ATP and UTP, respectively.
Stimulation of the cells with ATP or UTP induced a rapid increase in intracellular Ca2+, followed by a slow decline to basal levels. Ca2+ responses reached lower maximal values and did not show the slow phase in the absence of extracellular Ca2+. The ATP and UTP‐evoked increase in intracellular Ca2+ was not additive and showed cross‐desensitization. Cross‐desensitization was absent in myotubes stimulated with one of the nucleotides and bradykinin.
These results show that ATP‐ and UTP‐induced formation of Ins(1,4,5)P3, Ca2+ release from internal stores and Ca2+‐influx from the extracellular space are mediated exclusively via the nucleotide type P2‐purinoceptor in mouse C2C12 myotubes.
Extracellular ATP and UTP activation of phospholipase D is mediated by protein kinase C‐ε in rat renal mesangial cells
Authors: Pfeilschifter Josef , Merriweather Claire 
Published: July 2012

We have studied whether a nucleotide receptor mediates the effects of extracellular ATP and UTP on phosphatidylcholine metabolism in rat cultured glomerular mesangial cells.
ATP and UTP stimulated a biphasic 1,2‐diacylglycerol (DAG) formation in [3H]‐arachidonic acid‐labelled mesangial cells. In contrast, in cells labelled with [3H]‐myristic acid, a tracer that preferentially marks phosphatidylcholine, both nucleotides induced a delayed monophasic production of DAG with a concomitant increase in phosphatidic acid and choline formation.
A phospholipase D‐mediated phosphatidylcholine hydrolysis was further suggested by the observation that ATP and UTP stimulate the accumulation of phosphatidylethanol, when ethanol was added to mesangial cells.
The rank order of potency of a series of nucleotide analogues for stimulation of phosphatidylethanol formation was UTP = ATP > ITP > ATPγS > βγ‐imido‐ATP = ADP > 2‐methylthio‐ATP = βγ‐methylene‐ATP = ADPβS, while AMP, adenosine, CTP and GTP were inactive, indicating the presence of a nucleotide receptor.
Elevation of cytosolic free Ca2+ by the calcium ionophore A23187 (1 μm) or the Ca2+‐ATPase inhibitor, thapsigargin (200 nm) slightly increased phosphatidylethanol formation. However, chelation of cytosolic Ca2+ with high concentrations of Quin 2 did not attenuate ATP‐ and UTP‐induced phosphatidylethanol production, thus suggesting that Ca2+ is not crucially involved in agonist‐stimulated phospholipase D activation.
The protein kinase C (PKC) activator, phorbol 12‐myristate 13‐acetate (PMA), but not the biologically inactive 4α‐phorbol 12,13‐didecanoate, increased phospholipase D activity in mesangial cells, suggesting that PKC may mediate nucleotide‐induced phosphatidylcholine hydrolysis.
Down‐regulation of PKC‐α and ‐δ isoenzymes by 8 h PMA treatment still resulted in full phospholipase D activation. In contrast, a 24 h treatment of mesangial cells with PMA, a regimen that also causes depletion of PKC‐ε, markedly attenuated nucleotide‐evoked phosphatidylethanol formation. In addition, the selective PKC inhibitor, calphostin C attenuated ATP‐ and UTP‐induced phosphatidylethanol production.
In summary, these data suggest that extracellular ATP and UTP use a common nucleotide receptor to activate phospholipase D‐mediated phosphatidylcholine hydrolysis. Stimulation of phospholipase D appears to involve the PKC‐ε isoenzyme, activated by DAG derived from phosphoinositide hydrolysis by phospholipase C.
Eicosanoid‐induced Ca2+ release and sustained contraction in Ca2+‐free media are mediated by different signal transduction pathways in rat aorta
Authors: Kurata Ryuichi , Takayanagi Issei , Hisayama Tetsuhiro 
Published: July 2012

The effects of 12‐O‐tetradecanoyl 4β‐phorbol 13‐acetate (β‐TPA) on the inositol 1,4,5‐trisphosphate (IP3) production, Ca2+ release from the intracellular Ca2+ stores and sensitization of contractile apparatus, induced by prostaglandin F2α (PGF2α) and U46619, a thromboxane A2‐mimetic, were studied, using fura‐2‐loaded and ‐unloaded rat thoracic aortic strips.
Both eicosanoids had characteristic patterns of responses in Ca2+‐free, 2 mm EGTA‐containing solution (Ca2+‐free solution). They induced transient increases in intracellular Ca2+ concentration ([Ca2+]i) without corresponding transient contraction, but produced delayed, sustained contraction, where [Ca2+]i was returned to the basal level.
Treatment with β‐TPA for 60 min reduced the eicosanoids‐induced IP3 production, suggesting that the treatment inhibits PIP2 breakdown.
The treatment also attenuated [Ca2+]i transient induced by the eicosanoids, but not by caffeine (an IP3‐independent releaser of stored Ca2+), in fura‐2‐loaded preparations incubated in Ca2+‐free solution.
In contrast in the presence of β‐TPA, the sustained contractions evoked by the eicosanoids in Ca2+‐free solution were potentiated, suggesting that the sites of actions of β‐TPA and the eicosanoids may differ from each other.
PGF2α and U46619 utilize different and parallel signal transduction pathways to release Ca2+ by IP3 produced by PIP2 breakdown (β‐TPA‐sensitive), and to increase the sensitivity of contractile apparatus, in which protein kinase C may not be involved (β‐TPA‐insensitive).
Pro‐inflammatory activities in elapid snake venoms
Authors: Tambourgi Denise V. , dos Santos Maria Cristina , Furtado Maria de Fátima D. , de Freitas Maria Cristina W. , Dias da Silva Wilmar , Kipnis Thereza L. 
Published: July 2012

Snake venoms from the genera Micrurus (M. ibiboboca and M. spixii) and Naja (N. naja, N. melanoleuca and N. nigricollis) were analysed, using biological and immunochemical methods, to detect pro‐inflammatory activities, cobra venom factor (COF), proteolytic enzymes, thrombin‐like substances, haemorrhagic and oedema‐producing substances.
The venoms of the five snake species activate the complement system (C) in normal human serum (NHS) in a dose‐related fashion, at concentrations ranging from 5 μg to 200 μg ml−1 serum. Electrophoretic conversion of C3 was observed with all venoms in NHS containing normal concentrations of Ca2+ and Mg2+, but only by venoms from N. naja and N. melanoleuca when Ca2+ was chelated by adding Mg2+‐EGTA.
Purified human C3 was electrophoretically converted, in the absence of other C components, by the venoms from N. naja, N. nigricollis and M. ibiboboca. However, only the venoms from N. naja and N. melanoleuca contained a 144 kDa protein revealed in Western blot with sera against COF or human C3.
All venoms, at minimum concentrations of 30 ng ml−1, were capable of lysing sheep red blood cells, also in a dose‐related fashion, when incubated with these cells in presence of egg yolk as a source of lecithin. Although the venoms from M. spixii and N. nigricollis showed detectable thrombin‐like activity, these and the other venoms were free of proteolytic activity when fibrin, gelatin and casein, were used as substrates.
When tested on mice skin, all five venoms were capable of inducing an increase in vascular permeability and oedema, but were devoid of haemorrhagic producing substances (haemorrhagins).
These data provide evidence indicating that Elapidae venoms contain various pro‐inflammatory factors which may be important in the spreading of neurotoxins throughout the tissues of the prey or human victim.
Mepacrine‐induced inhibition of the inward current mediated by 5‐HT3 receptors in rat nodose ganglion neurones
Authors: Fan Ping 
Published: July 2012

With the whole‐cell patch clamp technique, the effect of the antimalarial drug, mepacrine (quinacrine) on the inward current mediated by 5‐HT3 receptors (5‐hydroxytryptamine (5‐HT)‐induced current) was investigated in isolated nodose ganglion neurones of the rat.
5‐HT and the selective 5‐HT3 receptor agonists, 2‐methyl‐5‐HT and m‐chlorophenylbiguanide elicited an inward current which reversed at around 0 mV and quickly desensitized to a steady state level.
Mepacrine dose‐dependently inhibited the peak current induced by 5‐HT with an IC50 of 2.1 μm and an apparent Hill coefficient of 0.99.
Mepacrine increased the decay rate of the 5‐HT‐induced current.
The effect of mepacrine on the 5‐HT‐induced current was reversible and not dependent on membrane potential. The reversal potential of the 5‐HT‐induced current was not affected.
Intracellular mepacrine had no significant effect on the 5‐HT‐induced current and did not block the extracellular action of mepacrine.
Concentration‐response curves in the presence and absence of mepacrine suggest a non‐competitive inhibition of 5‐HT‐induced current by mepacrine.