bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synergistic inhibition of thrombin‐induced platelet aggregation by the novel nitric oxide‐donor GEA 3175 and adenosine
Authors: Grenegård M. , Gustafsson M.C. , Andersson R.G.G. , Bengtsson T. 
Published: July 2012

The influence of the novel nitric oxide‐donor GEA 3175 on thrombin‐ and ionomycin‐stimulated human platelets was investigated. The effect of GEA 3175 was compared with that of adenosine, an activator of platelet adenylyl cyclase.
GEA 3175 inhibited thrombin‐induced secretion of ATP but did not affect aggregation; similar results were obtained with adenosine.
Thrombin‐stimulated rises in the cytosolic free Ca2+ concentration, [Ca2+]i, were dose‐dependently inhibited by GEA 3175 and adenosine. GEA 3175 and adenosine maximally reduced the initial rise in [Ca2+]i by 41% and 35%, respectively.
Simultaneous exposure to GEA 3175 and adenosine nearly abolished both the functional responses (i.e. aggregation and degranulation) and the rises in [Ca2+]i in thrombin‐stimulated platelets.
Aggregation and increases in [Ca2+]i triggered in platelets by the Ca2+‐ionophore ionomycin were only marginally affected by a combination of GEA 3175 and adenosine.
GEA 3175 potently increased the guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) content in platelets but did not affect adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels. Adenosine did not increase either the cyclic AMP or the cyclic GMP levels in platelets. However, adenosine and GEA 3175 combined significantly elevated the platelet cyclic AMP content.
The results show that simultaneous exposure to GEA 3175 and adenosine promotes potent anti‐aggregatory properties in platelets in vitro. The findings suggest that blockage of the cytosolic Ca2+‐signal, which is probably mediated by an amplified cyclic nucleotide response, is an important event during the synergistic inhibition of thrombin‐induced aggregation.
Role of sarcoplasmic reticulum in inhibitory junction potentials and hyperpolarizations by nitric oxide donors in opossum oesophagus
Authors: Cayabyab Francisco S. , Daniel Edwin E. 
Published: July 2012

Previous patch clamp studies of oesophageal circular muscle cells showed that nitric oxide (NO) modulated the opening of Ca2+‐activated K+ channels involved in mediating the inhibitory junction potentials (i.j.ps). This study clarified the role of Ca2+ release from the superficial sarcoplasmic reticulum (SR) in the mechanism of i.j.ps or hyperpolarizing responses to NO‐releasing compounds. Electrical and mechanical activities were simultaneously recorded by intracellular microelectrode or double sucrose gap techniques.
The NO‐donors, sydnonimine (SIN‐1) and sodium nitroprusside, each at 500 μm, hyperpolarized oesophageal circular muscle cells by 15–20 mV, like i.j.ps.
The selective inhibitors of SR Ca2+‐ATPase (cyclopiazonic acid 10–30 μm and thapsigargin 5 μm) and the SR Ca2+ release channel activator (ryanodine 30 μm) caused depolarization and spontaneous contractions which were diminished after prolonged (>30 min) incubation with these agents in Ca2+‐containing medium. Moreover, these agents inhibited both the i.j.p. and NO‐donor hyperpolarizations, suggesting that a functional SR Ca2+ uptake is necessary for the response to endogenous or exogenous NO.
These results, along with our previous findings of the dependence of i.j.ps and NO‐donor hyperpolarizations on K+ channel activation and cyclic GMP elevation, support the hypothesis that subplasmalemmal Cai2+ elevation, via vectorial Ca2+ release from superficial SR toward the plasmalemma, may be an important mechanism by which NO, from NO‐liberating compounds or released from inhibitory neurones induces relaxation and i.j.ps in opossum oesophagus.
The effect of insulin treatment and of islet transplantation on the resistance artery function in the STZ‐induced diabetic rat
Authors: Heygate Katherine M. , Davies Joanne , Holmes Michael , James Roger F.L. , Thurston Herbert 
Published: July 2012

This study was designed to investigate the influence of insulin treatment and islet transplantation on the smooth muscle contractility and endothelium‐dependent and independent relaxation of resistance arteries in the chemically induced streptozotocin (STZ) diabetic rat after 6–8 weeks, and 12–14 weeks of diabetes, compared to non‐diabetic age‐matched controls.
The morphology, and contractile responses to high potassium physiological salt solution (KPSS), KPSS containing 10−5 m noradrenaline (NAK), and concentration‐response curves to noradrenaline (NA) of mesenteric resistance arteries were recorded, along with the endothelium‐dependent relaxation responses to acetylcholine (ACh) and bradykinin (BK), and endothelium‐independent relaxation to sodium nitroprusside (SNP). Concentration‐response curves were then repeated in the presence of a nitric oxide synthase inhibitor, NG‐nitro‐L‐arginine (L‐NOARG).
Insulin‐treated diabetic rats in the 12 week study demonstrated enhanced vascular contractility to KPSS, NAK and NA, compared to age‐matched non‐diabetic controls.
Incubation with L‐NOARG resulted in both a significant increase in maximum contractile response, and sensitivity (pD2) to NA in the untreated diabetic group (6 weeks). A significant shift in sensitivity was also seen in the insulin‐treated diabetic group. In the 12 week study, incubation with L‐NOARG resulted in an increased maximum contractile response and sensitivity to NA in the insulin‐treated diabetics. An increase in sensitivity was also observed in the untreated diabetic group.
Endothelium‐dependent relaxation to ACh was significantly augmented in the untreated diabetics (6‐weeks), compared to the control group. In the 12‐week study, relaxation to both ACh and BK was not significantly different in any of the experimental groups when compared to the sham‐operated non‐diabetic controls.
Incubation with L‐NOARG resulted in a significant attenuation of the maximum relaxation response to ACh and BK in all of the experimental groups, in the 6‐ and the 12‐week study.
There was no significant difference in the maximum relaxation response or sensitivity to sodium nitroprusside between the diabetic groups and their age‐matched controls in either the 6‐week or the 12‐week study.
The results of this study suggest an enhanced release of nitric oxide in the early stages of diabetes, which is more evident in the untreated diabetic rats than the insulin treated, and appears to normalize as the duration of diabetes progresses. This study also shows that the alteration in vascular reactivity of the resistance arteries can be restored to within normal limits by the transplantation of islets of Langerhans, and that islet transplantation is an effective strategy in the correction of the metabolic abnormalities associated with insulin‐dependent diabetes.
Effects of purinoceptor agonists on cytosolic Ca2+ concentration in swine tracheal smooth muscle cells in culture
Authors: Sawai Hiroko , Wang Ruixia , Yamashita Toshikazu , Kokubun Shinichiro 
Published: July 2012

The effects of various purinoceptor agonists on intracellular Ca2+ concentration ([Ca2+]i) in swine tracheal smooth muscle cells in primary culture were examined to investigate the subtype of purinoceptors in these cells.
ATP (1 μm to 1 mM) concentration‐dependently increased [Ca2+]i which was measured by monitoring the fluorescence signal of fura2.
α, β‐Me ATP at concentrations higher than 10 μm increased [Ca2+]i in the presence of extracellular Ca2+. Responses to the drug were 12 ± 5 and 61 ± 4% of responses to ATP (100 μm) at 100 μm and 1 mM, respectively (n = 7). The response to 100 μm ATP was inhibited by 62% in the presence of 1 mM α, β‐Me ATP (n = 8), though the drug at concentrations lower than that did not affect the response to ATP.
ATP increased [Ca2+]i in the absence of extracellular Ca2+. The response to ATP in this condition was 40% of that in the presence of extracellular Ca2+ (n = 8).
Neither cibacron blue 3GA (10 μm) (n = 8) nor suramin (10 and 100 μm) (n = 10) affected the response to ATP (1 μm to 100 μm).
The rank order of potency in the absence of extracellular Ca2+ was UTP> ATP> adenosine 5′‐o‐(3‐thiotriphosphate)>> ADP = α, β‐methylene adenosine 5′‐triphosphate > 2‐(methylthio)‐adenosine 5′‐(tetrahydrogen triphosphate).
UTP (1 μm to 100 μm) concentration‐dependently increased inositol 1,4,5‐triphosphate (IP3) production.
These results suggest that the increase in [Ca2+]i induced by purinoceptor agonists is mediated mainly via a nucleotide receptor in swine tracheal smooth muscle cells in primary culture.
Effects of cantharidin on force of contraction and phosphatase activity in nonfailing and failing human hearts
Authors: Linck Bettina , Boknik Peter , Knapp Jörg , Müller Frank U. , Neumann Joachim , Schmitz Wilhelm , Vahlensieck Ute 
Published: July 2012

The effect of the phosphatase inhibitor, cantharidin (3–300 μm) on force of contraction was studied in isolated electrically driven right ventricular trabeculae carneae from human myocardium.
The positive inotropic effect of cantharidin started at a concentration of 100 μm with a positive inotropic effect to 199% and to 276% of the predrug value in nonfailing and failing human hearts, respectively.
Under basal conditions the contraction time parameters were prolonged in human heart failure vs. nonfailing preparations. However, the positive inotropic effect of cantharidin did not affect contraction time parameters. Thus, time to peak tension, time of relaxation and total contraction time were not shortened by cantharidin in nonfailing and failing preparations.
The phosphatase activity was unchanged in preparations from failing hearts compared to nonfailing hearts.
Cantharidin inhibited phosphatase activity in a concentration‐dependent manner. The IC50 value of cantharidin was about 3 μm in both nonfailing and failing human myocardium.
The positive inotropic effect of cantharidin was similar in nonfailing and failing human hearts, accompanied by a similar inhibitory effect of cantharidin on the phosphatase activity. The positive inotropic effect of cantharidin in failing hearts was as strong as the effect of isoprenaline in nonfailing hearts.
It is concluded that the treatment with a phosphatase inhibitor may offer a new positive inotropic modality for the treatment of human heart failure.
Effects of memantine on recombinant rat NMDA receptors expressed in HEK 293 cells
Authors: Bresink Iris , Benke Timothy A. , Collett Valerie J. , Seal Andy J. , Parsons Chris G. , Henley Jeremy M. , Collingridge Graham L. 
Published: July 2012

The actions of the uncompetitive N‐methyl‐d‐aspartate (NMDA) receptor antagonists, memantine (1‐amino‐3,5‐dimethyladamantane) and (+)‐MK‐801 ((+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine maleate, dizocilpine), on recombinant NMDA receptors has been studied by use of the whole‐cell patch clamp technique.
Human embryonic kidney (HEK) 293 cells were transiently transfected with different NMDA receptor subunit combinations (NR1a/NR2A, NR1a/NR2B and NR1a/NR2D). A mutant form of the green fluorescent protein (GFP) was cotransfected with the NMDA receptor subunits to enable the visualization of transfected cells.
Memantine (0.3–30 μm) blocked L‐glutamate (100 μm)‐mediated currents in a concentration‐dependent manner in NR1a/NR2A, NR1a/NR2B and NR1a/NR2D transfected cells with IC50 values (at −70 mV) of 0.93±0.15 μm, 0.82±0.12 μm and 0.47±0.06 μm (mean±s.e. mean), respectively.
The memantine‐induced block was strongly voltage‐dependent. Alteration of the holding potential from −70 mV to +60 mV resulted in an e‐fold increase in the IC50 values per 30–33 mV change in membrane potential, for all 3 subunit combinations investigated.
The kinetics of the actions of memantine (30 μm) were investigated for the NR1a/2A combination, in 6 cells (13–15 determinations). At −70 mV, the block and recovery from block were both best described by two exponentials with time‐constants of 201±23 ms (81±2%) and 3.9±0.6 s and 597±94 ms (18±1%) and 18.6±2.4 s, respectively. The predominant effect of depolarization was to increase the weight of the faster recovery time‐constant. Kinetic analysis suggests that these results are consistent with previously proposed Markov models.
(+)‐MK‐801 was studied briefly for comparative purposes. (+)‐MK‐801 (200 nM) preferentially blocked NMDA receptor currents (at −70 mV) in NR1a/NR2A and NR1a/NR2B (82±10% and 93±2% depressions) compared to NR1a/NR2D (38±7%) transfected cells. (+)‐MK‐801 appeared to be less voltage‐dependent than memantine on all three receptor combinations.
In conclusion, memantine was a voltage‐dependent antagonist of recombinant rat NMDA receptors expressed in HEK 293 cells but showed little selectivity between the subunits investigated. Its actions on these recombinant receptor combinations are similar to its actions on native NMDA receptors.
Neuropeptide Y Y2 receptor‐mediated attenuation of neurogenic plasma extravasation acting through pertussis toxin‐sensitive mechanisms
Authors: Yu Xian‐Jie , Moskowitz Michael A. 
Published: July 2012

The effects of neuropeptide Y (NPY) receptor agonists (administered intravenously) were examined on plasma protein ([125I]‐bovine serum albumin) leakage within dura mater evoked by unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min), capsaicin (1 μmol kg−1, i.v.) or substance P (1 nmol kg−1, i.v.) in anaesthetized Sprague‐Dawley rats.
NPY (EC50: 5.6 nmol kg−1) and NPY fragment 13–36 [NPY (13–36)] (ED50: 4.3 nmol kg−1), an NPY Y2 receptor agonist, dose‐dependently attenuated [125I]‐bovine serum albumin extravasation from meningeal vessels when administered 10 min prior to electrical stimulation. [Leu31, Pro34]‐NPY, an NPY Y1 and Y3 receptor agonist, inhibited the response at a higher dose only (23 nmol kg−1) (P < 0.05).
NPY also significantly decreased plasma protein extravasation induced by capsaicin (1 μmol kg−1) but not by substance P (1 nmol kg−1).
Pertussis toxin (20 μg kg−1, administered intracisternally 48 h prior to stimulation) blocked completely the inhibitory effect of NPY and NPY (13–36) but did not inhibit extravasation alone.
We conclude that NPY inhibits neurogenically‐mediated plasma protein extravasation acting through presynaptic pertussis toxin‐sensitive NPY Y2 receptors, possibly by inhibition of neuropeptide release from perivascular trigeminovascular afferents.
Preferential activation of excitatory adenosine receptors at rat hippocampal and neuromuscular synapses by adenosine formed from released adenine nucleotides
Authors: Cunha Rodrigo A. , Correia‐de‐Sá Paulo , Sebastião Ana M. , Ribeiro J. Alexandre 
Published: July 2012

In the present work, we investigated the action of adenosine originating from extracellular catabolism of adenine nucleotides, in two preparations where synaptic transmission is modulated by both inhibitory A1 and excitatory A2a‐adenosine receptors, the rat hippocampal Schaffer fibres/CA1 pyramid synapses and the rat innervated hemidiaphragm.
Endogenous adenosine tonically inhibited synaptic transmission, since 0.5‐2 u ml−1 of adenosine deaminase increased both the population spike amplitude (30 ± 4%) and field excitatory post‐synaptic potential (f.e.p.s.p.) slope (27 ± 4%) recorded from hippocampal slices and the evoked [3H]‐acetylcholine ([3H]‐ACh) release from the motor nerve terminals (25 ± 2%).
a, b̊‐Methylene adenosine diphosphate (AOPCP) in concentrations (100–200 μm) that almost completely inhibited the formation of adenosine from the extracellular catabolism of AMP, decreased population spike amplitude by 39 ± 5% and f.e.p.s.p. slope by 32 ± 3% in hippocampal slices and [3H]‐ACh release from motor nerve terminals by 27 ± 3%.
Addition of exogenous 5′‐nucleotidase (5 u Ml−1) prevented the inhibitory effect of AOPCP on population spike amplitude and f.e.p.s.p. slope by 43–57%, whereas the P2 antagonist, suramin (100 μm), did not modify the effect of AOPCP.
In both preparations, the effect of AOPCP resulted from prevention of adenosine formation since it was no longer evident when accumulation of extracellular adenosine was hindered by adenosine deaminase (0.5‐2 u ml−1). The inhibitory effect of AOPCP was still evident when A1 receptors were blocked by 1,3‐dipropyl‐8‐cyclopentylxanthine (2.5‐5 nM), but was abolished by the A2 antagonist, 3,7‐dimethyl‐1‐propargylxanthine (10 μm).
These results suggest that adenosine originating from catabolism of released adenine nucleotides preferentially activates excitatory A2 receptors in hippocampal CA1 pyramid synapses and in phrenic motor nerve endings.
Evidence for 5‐HT1‐like receptor‐mediated vasoconstriction in human pulmonary artery
Authors: MacLean Margaret R. , Clayton Robin A. , Templeton Alison G.B. , Morecroft Ian 
Published: July 2012

The 5‐hydroxytryptamine (5‐HT) receptors mediating contraction of human isolated pulmonary artery rings were investigated. Responses to the agonists 5‐carboximidotryptamine (5‐CT, non‐selective 5‐HT1 agonist), sumatriptan (5‐HT1D‐like receptor agonist), 5‐HT and 8‐hydroxy‐2‐(di‐n‐propylamino)‐tetralin (8‐OH‐DPAT, 5‐HT1A receptor agonist) were studied. Responses to 5‐HT and sumatriptan in the presence of the antagonists, methiothepin (non‐selective 5‐HT1+2‐receptor antagonist), ketanserin (5‐HT2A receptor antagonist) and the novel antagonist, GR55562 (5‐HT1D receptor antagonist) were also studied.
All agonists contracted human pulmonary artery ring preparations in the following order of potency 5‐CT > 5‐HT = sumatriptan > 8‐OH‐DPAT. Maximum responses to 5‐HT, 5‐CT and sumatriptan were not significantly different.
Methiothepin 1 nM and 10 nM, but not 0.1 nM reduced the maximum contractile responses to 5‐HT but did not alter tissue sensitivity to 5‐HT. Methiothepin 0.1 nM, 1 nM and 10 nM had a similar effect on responses to sumatriptan.
The 5‐HT2A receptor antagonist ketanserin (10 nM, 100 nM and 1 μm) also reduced the maximum contractile response to both 5‐HT and sumatriptan without affecting tissue sensitivity to these agonists.
The novel 5‐HT1D receptor antagonist, GR55562, inhibited responses to 5‐HT and sumatriptan in a true competitive fashion.
The results suggest that the human pulmonary artery has a functional population of 5‐HT1D‐like receptors which are involved in the contractile response to 5‐HT.
Pharmacological characterization of the 5‐hydroxytryptamine receptor mediating relaxation in the rat isolated ileum
Authors: Tuladhar B.R. , Costal B. , Naylor R.J. 
Published: July 2012

The aim of the present study was to investigate a 5‐HT4 receptor involvement in the mediation of a 5‐HT‐induced relaxation response in the rat isolated ileum in vitro.
Ileal segments were taken at regular intervals from the ileo‐caecal junction to duodenum. 5‐HT (1 μm) induced a relaxation or contraction response in segments taken from the terminal ileum: the relaxation decreased and finally disappeared as contractions dominated in the proximal tissues. The 5‐HT‐induced relaxations were enhanced in the terminal segments and the contractions attenuated in both terminal and proximal segments, in the presence of methysergide (1 μm) and atropine (0.1 μm).
In the presence of methysergide (1 μm) and atropine (0.1 μm), a cumulative addition of 5‐HT (0.01‐1 μm) induced a concentration‐dependent relaxation in the terminal (1–20 cm from the ileo‐ceacal junction) ileal segments which at higher concentrations of 5‐HT (3–30 μm) reverted to contraction.
The rank order of potency of indole agonists in inducing a concentration‐related relaxation response in tissues of the terminal ileum (pretreated with pargyline (100 μm) and in the presence of methysergide (1 or 100 μm) and atropine (0.1 μm)) was 5‐hydroxytryptamine (6.97 ± 0.06), 5‐methoxytryptamine (6.50 ± 0.07), α‐methyl‐5‐hydroxytryptamine (5.53 ± 0.17), 5‐carboxamidotryptamine (5.51 ± 0.12) and 2‐methyl‐5‐hydroxytryptamine (< 5), the pEC50 values (mean ± s.e.mean) being shown in parentheses.
Pretreatment of tissues with pargyline (100 μm) selectively enhanced the potency of 5‐methoxytryptamine by a factor of 19 but failed to modify the potency of the other indole agonists.
The 5‐HT4 receptor antagonists, tropisetron, SDZ 205–557 and GR 113808 antagonized the relaxation response to 5‐HT (in the presence of methysergide (1 or 10 μm) and atropine (0.1 μm)) with pKB values (95% CL) of 6.09 (5.94‐6.24), 7.0 (6.9‐7.09) and 8.95 (8.81‐9.1) respectively. Apparent pKB values estimations for tropisetron (1 μm) and GR 113808 (10 nM) using the agonists 5‐methoxytryptamine and 5‐carboxamidotryptamine were 6.37 ± 0.31, 5.91 ± 0.38 and 8.83 ± 0.11, 8.82 ± 0.22 respectively.
Tropisetron (10 μm), SDZ 205–557 (3 μm) and GR 113808 (10–100 nM) caused an increase in basal tone of the rat terminal ileum when administered in the presence of methysergide and atropine.
The relaxation response to 5‐HT in the rat terminal ileum was not antagonized by ritanserin (1 μm), ondansetron (1 μm) or Nω‐nitro‐l‐arginine methyl ester (100 μm) and with only a twofold dextral shift of the concentration‐response curve by tetrodotoxin (1 μm).
It is concluded that the relaxant response to 5‐HT in the terminal region of the ileum is mediated directly at the smooth muscle; a ranked indole agonist potency and selective antagonism by 5‐HT4 receptor antagonists tropisetron, SDZ 205–557 and GR 113808 indicate a 5‐HT4 receptor involvement in the relaxation response.
The increase in human plasma immunoreactive endothelin but not big endothelin‐1 or its C‐terminal fragment induced by systemic administration of the endothelin antagonist TAK‐044
Authors: Plumpton Christopher , Ferro Charles J. , Haynes William G. , Webb David J. , Davenport Anthony P. 
Published: July 2012

We examined the effects of systemic infusion, in healthy human volunteers, of the endothelin antagonist TAK‐044 on the plasma concentrations of mature endothelin, big endothelin‐1 and the C‐terminal fragment of big endothelin‐1, by selective solid‐phase extraction and specific radioimmunoassays.
Unlabelled TAK‐044 competed with specific [125I]‐endothelin‐1 binding to human left ventricle tissue in a biphasic manner giving KD values of 0.11 nM and 26.8 nM at the ETA and ETB receptor subtypes, respectively, indicating a 244 fold selectivity for the ETA receptor subtype.
A 15 min intravenous infusion of placebo or 30 mg TAK‐044 (giving a serum concentration of 2 nM, calculated to block > 95% of ETA but <5% ETB receptors) had no effect on the immunoreactive plasma concentrations of the three peptides.
At the higher dose of 750 mg TAK‐044 (giving a serum concentration of 80 nM, calculated to block > 99% of ETA and > 75% ETB receptors), the immunoreactive plasma endothelin concentrations were increased 3.3 fold over basal levels (P < 0.01). The concentrations of big endothelin‐1 or C‐terminal fragment of big endothelin‐1 were unchanged.
At both doses of TAK‐044, there were significant decreases in diastolic blood pressure, and peripheral vascular resistance, with corresponding increases in cardiac index and stroke index. There were no changes in systolic or mean arterial blood pressures or heart rate.
Since only the concentrations of the mature peptide were increased, we conclude that the most likely sources of endothelin contributing to the observed rise were displacement of receptor‐bound peptide and reduction in plasma clearance rather than peptide synthesis.