bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of dopamine and noradrenaline release and of intracellular Ca2+ concentration by presynaptic glutamate receptors in hippocampus
Authors: Malva João O. , Carvalho Arsélio P. , Carvalho Caetana M. 
Published: July 2012

We studied the release of [3H]‐dopamine and [3H]‐noradrenaline (NA) from hippocampal synap‐tosomes induced by glutamate receptors and the associated Ca2+ influx through Ca2+ channels. The release of tritiated neurotransmitters was studied by use of superfusion system and the intracellular free Ca2+ concentration ([Ca2+]i) was determined by a fluorimetric assay with Indo‐1 as a probe for Ca2+.
Presynaptic glutamate receptor activation induced Ca2+‐dependent release of [3H]‐dopamine and [3H]‐NA from rat hippocampal synaptosomes. Thus, L‐glutamate induced the release of both neurotransmitters in a dose‐dependent manner (EC50 = 5.62 μm), and the effect of 100 μm L‐glutamate was inhibited by 83.8% in the presence of 10 μm 6‐cyano‐7‐nitroquinoxaline‐2,3‐dioxine (CNQX), but was not affected by 1 μm (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]‐cyclohepten‐5,10‐imine (MK‐801).
Other glutamate receptor agonists also stimulated the Ca2+‐dependent release of [3H]‐dopamine and [3H]‐NA as follows: N‐methyl‐D‐aspartate (NMDA), at 200 μm, released 3.65 ± 0.23% of the total 3H catecholamines, and this effect was inhibited by 81.2% in the presence of 1 μm MK‐801; quisqualate (50 μm), S‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolopropionic acid (AMPA) (100 μm) or kainate (100 μm) released 1.57 ± 0.26%, 1.93 ± 0.17% and 2.09 ± 0.22%, of the total 3H catecholamines, respectively.
The ionotropic glutamate receptor agonist, AMPA, induced an increase in the [Ca2+]i which was inhibited by 58.6% in the presence of 10 μm CNQX. In contrast, the increase in [Ca2+]i due to stimulation by glutamate was not sensitive to CNQX or MK–801.
Nitrendipine, at 1 μm, did not inhibit the neurotransmitter release induced by AMPA, but, both 0.5 μm ω‐conotoxin GVIA (μ‐CgTx) and 100 nm μ‐Aga IVA reduced catecholamine release to 49.03 ± 3.79% and 46.06 ± 10.51% of the control, respectively. In the presence of both toxins the release was reduced to 12.58 ± 4.64% of the control.
The results indicate that activation of presynaptic glutamate receptors of the NMDA and non‐NMDA type induces the release of [3H]‐dopamine and [3H]‐NA from rat hippocampal synaptosomes and that the release induced by AMPA involves the activation of N‐ and P‐type Ca2+ channels which allow the influx of Ca2+ that triggers the 3H catecholamines release.
Stimulation by extracellular ATP and UTP of the mitogen‐activated protein kinase cascade and proliferation of rat renal mesangial cells
Authors: Huwiler Andrea , Pfeilschifter Josef 
Published: July 2012

Extracellular ATP and UTP have been reported to activate a nucleotide receptor that mediates phosphoinositide and phosphatidylcholine hydrolysis by phospholipases C and D, respectively. Here we report that ATP and UTP potently stimulate mesangial cell proliferation.
Both nucleotides stimulate phosphorylation and activation of mitogen‐activated protein kinase and a biphasic phosphorylation of the up‐stream mitogen‐activated protein kinase kinase.
When added at 100 μm, ATPγS, UTP and ATP were the most potent activators of mitogen‐activated protein kinase. βγ‐imido‐ATP was somewhat less active and ADP and 2‐methylthio‐ATP caused a weak induction of enzyme activity. Activation of mitogen‐activated protein kinase by both ATP and UTP is dose‐dependently attenuated by the P2‐receptor antagonist, suramin.
The protein kinase C activator 12‐0‐tetradecanoylphorbol 13‐acetate, but not the biologically inactive 4α‐phorbol 12,13‐didecanoate, increased mitogen‐activated protein kinase activity in mesangial cells, suggesting that protein kinase C may mediate nucleotide‐induced stimulation of mitogen‐activated protein kinase.
Down‐regulation of protein kinase C ‐α and‐θ isoenzymes by 4 h or 8 h treatment with phorbol ester partially inhibited ATP‐ and UTP‐triggered mitogen‐activated protein kinase activation. Moreover, a 24 h treatment of mesangial cells with phorbol ester, a regimen that also causes depletion of protein kinase C‐∍ did not further reduce the level of mitogen‐activated protein kinase stimulation.
The specific protein kinase C inhibitor, CGP 41251, which displayed a selectivity for the Ca2+‐dependent isoenzymes, as compared to the Ca2+‐independent isoenzymes did not inhibit nucleotide‐stimulated mitogen‐activated protein kinase phosphorylation, thus implicating the involvement of a Ca2+‐independent protein kinase C isoform.
In summary, these results suggest that ATP and UTP trigger the activation of the mitogen‐activated protein kinase signalling cascade in mesangial cells and this may be responsible for the potent mitogenic activity of both nucleotides.
GABA and glutamate release affected by GABAB receptor antagonists with similar potency: no evidence for pharmacologically different presynaptic receptors
Authors: Waldmeier Peter C. , Wicki Peter , Feldtrauer Jean‐Jacques , Mickel Stuart J. , Bittiger Helmut , Baumann Peter A. 
Published: July 2012

The effects of a series of nine GABAB receptor antagonists of widely varying potencies on electrically stimulated release from cortical slices of [3H]‐GABA in the absence or presence of 10 μm of the GABABagonist, (−)−baclofen and of endogenous glutamate in the presence of (−)−baclofen were compared.
The concentrations of the compounds half maximally increasing [3H]‐GABA release (EC50's) at a stimulation frequency of 2 Hz correlated well with the IC50 values obtained from the inhibition of the binding of the agonist, [3H]‐CGP 27492, to GABAB receptors in rat brain membranes (rank order of potency: CGP 56999 A ≥ CGP 55845 A > CGP 52432 ≥ CGP 56433 A > CGP 57034 A > CGP 57070 A ≥ CGP 57976 > CGP 51176 > CGP 35348).
Likewise, the concentrations causing half‐maximal increases of [3H]‐GABA in the absence or presence of (−)−baclofen, and of endogenous glutamate in the presence of (−)−baclofen, correlated well with each other. Reports in the literature suggesting the CGP 35348 exhibits a 70 fold preference for inhibition of (−)−baclofen's effects on glutamate over [3H]‐GABA release, and that CGP 52432 shows a 100 fold preference in the opposite sense, could not be confirmed in our model.
Therefore, our results suggest that, if there are pharmacological differences between GABAB autoreceptors and GABAB heteroreceptors on glutamatergic nerve endings in the rat cortex, they are not revealed by this series of compounds of widely different potencies.
In particular, our results with CGP 35348 and CGP 52432 do not support the hypothesis that GABAB autoreceptors and GABAB heteroreceptors on glutamatergic nerve endings represent subtypes with different pharmacology.
Display of the characteristics of endothelium‐derived hyperpolarizing factor by a cytochrome P450‐derived arachidonic acid metabolite in the coronary microcirculation
Authors: Bauersachs Johann , Hecker Markus , Busse Rudi 
Published: July 2012

In addition to nitric oxide (NO) and prostacyclin (PGI2) an endothelium‐derived factor, which hyperpolarizes vascular smooth muscle cells via activation of K+ channels, contributes to the dilator effect of bradykinin in different vascular beds. Since this so‐called endothelium‐derived hyperpolarizing factor (EDHF) also seems to play an important role in the coronary circulation, we investigated its nature and mechanism of action in the rat isolated perfused heart (Langendorff preparation).
Bolus injections of bradykinin (1, 10, and 100 pmol) elicited a transient dose‐dependent dilator response (e.g., 12 ± 2% decrease in coronary perfusion pressure (CPP) at 10 pmol bradykinin, n = 41). Administration of the cyclo‐oxygenase inhibitor, diclofenac (1 μm), augmented the bradykinin‐induced dilation approximately twofold (n = 9 P < 0.01). Combined treatment with the NO synthase inhibitor, NG‐nitro‐L‐arginine (30 μm) and diclofenac (1 μm) significantly reduced the duration, but increased the amplitude of the dilator response to bradykinin (27 ± 2% decrease in CPP, n = 24, P < 0.01).
The abolition of this NG‐nitro‐L‐arginine/diclofenac‐insensitive dilator response to bradykinin by tetrabutylammonium (0.3 μm), an inhibitor of Ca2+‐dependent K+ channels (4 ± 1% decrease in CPP, n = 6, P < 0.01), supports the view that the dilator compound released in the coronary microcirculation is EDHF.
This EDHF‐type dilation was reversibly inhibited by the phospholipase A2 inhibitor, quinacrine (3 μm, 9 ± 3% decrease in CPP, n = 6, P < 0.01) and by the cytochrome P450 inhibitor SKF525a (3 μm, 6 ± 1% decrease in CPP, n = 6, P < 0.01).
Tetrabutylammonium, quinacrine or SKF 525a did not affect the endothelium‐independent dilator response to sodium nitroprusside (1 nmol), indicating that these compounds did not affect smooth muscle relaxation in a non‐specific manner.
These findings suggest that in the coronary microcirculation bradykinin stimulates the release of a cytochrome P450‐derived arachidonic acid metabolite, which exhibits the characteristic features of EDHF.
Cyclic GMP‐mediated inhibition of L‐type Ca2+ channel activity by human natriuretic peptide in rabbit heart cells
Authors: Tohse Noritsugu , Nakaya Haruaki , Kanno Youji Takeda & Morio 
Published: July 2012

Effects of atrial natriuretic peptide (ANP) on the L‐type Ca2+ channels were examined in rabbit isolated ventricular cells by use of whole‐cell and cell‐attached configurations of the patch clamp methods. ANP produced a concentration‐dependent decrease (10–100 nm) in amplitude of a basal Ca2+ channel current.
The inactive ANP (methionine‐oxidized ANP, 30 nm) failed to decrease the current.
8‐Bromo‐cyclic GMP (300 μm), a potent activator of cyclic GMP‐dependent protein kinase (PKG), produced the same effects on the basal Ca2+ channel current as those produced by ANP. The cyclic GMP‐induced inhibition of the Ca2+ channel current was still evoked in the presence of 1‐isobutyl‐3‐methyl‐xanthine, an inhibitor of phosphodiesterase. ANP failed to produce inhibition of the Ca2+ channel current in the presence of 8‐bromo‐cyclic GMP.
In the single channel recording, ANP and 8‐bromo‐cyclic GMP also inhibited the activities of the L‐type Ca2+ channels. Both agents decreased the open probability (NP0) without affecting the unit amplitude.
The present results suggest that ANP inhibits the cardiac L‐type Ca2+ channel activity through the intracellular production of cyclic GMP and then activation of PKG.
Endothelin ETA and ETB mRNA and receptors expressed by smooth muscle in the human vasculature: majority of the ETA sub‐type
Authors: Davenport Anthony P. , O'Reilly Gillian , Kuc Rhoda E. 
Published: July 2012

1 We measured the ratio of ETA and ETB sub‐types in the media (containing mainly smooth muscle) of human cardiac arteries (aorta, pulmonary and coronary), internal mammary arteries and saphenous veins.2 In saturation experiments, [125I]‐endothelin‐1 ([125I]‐ET‐1) bound with high affinity to the media of each vessel (n = 3 individuals or homogenate preparations ± s.e.mean): coronary artery, KD = 0.14 ± 0.02 nm, Bmax = 71.0 ± 21.0 fmol mg−1 protein; pulmonary artery, KD = 0.85 ± 0.25 nm, Bmax = 15.2 ± 10.3 fmol mg−1 protein; aorta, KD = 0.51 ± 0.02 nm, Bmax = 9.4 ± 4.4 fmol mg−1 protein; internal mammary artery, KD = 0.34 ± 0.31 nm, Bmax = 2.0 ± 0.5 fmol mg−1 protein and saphenous vein, KD = 0.28 ± 0.05 nm, Bmax = 52.8 ± 1.0 fmol mg−1 protein. In each vessel, over the concentration‐range tested, Hill slopes were close to unity and a one site fit was preferred to a two site model.3 In competition binding assays, the ETA selective ligand, BQ123 inhibited the binding of 0.1 nm [125I]‐ET‐1 to the media in a biphasic manner. In each case, a two site fit was preferred to a one or three site model: coronary artery, KDETA = 0.85 ± 0.03 nm, KDETB = 7.58 ± 2.27 μm, ratio = 89:11%; pulmonary artery, KDETA = 0.27 ± 0.05 nm, KDETB = 24.60 ± 5.34 μm, ratio = 92:8%; aorta, KDETA = 0.80 ± 0.40 nm, KDETB = 2.67 ± 2.60 μm ratio = 89:11%; saphenous vein, KDETA = 0.55 ± 0.17 nm, KDETB = 14.4 ± 0.26 μm, 85:15% (n = 3 individuals or homogenate preparations ± s.e.mean). BQ123 showed up to 18000 fold selectivity for the ETA over the ETB sub‐type. The ETA‐selective ligand, [125I]‐PD151242 labelled 85% of the receptors detected by a fixed concentration of [125I]‐ET‐1 in media of internal mammary artery, measured by quantitative autoradiography. In contrast, the density of ETB receptors detected with [125I]‐BQ3020 was 7.0 ± 1.5 amol mm−2, representing about 8% of [125I]‐ET‐1.4 A single band corresponding to the expected position for mRNA encoding the ETA receptor (299 base pairs) was found in the media in each of the five vessels (n = 3 individuals) using reverse‐transcriptase polymerase chain reaction assays. A single band corresponding to the ETB sub‐type (428 base pairs) was also always detected.5 35S‐labelled antisense probes to ETA and ETB hybridised to the media of epicardial coronary arteries as well as intramyocardial vessels, confirming the presence of mRNA encoding both sub‐types in the vascular smooth muscle of the vessel wall.6 Although mRNA for both receptors was detected, competition binding using BQ123 demonstrated that the majority (at least 85%) of ET receptors present in smooth muscle are the ETA sub‐type. These results provide further support for the hypothesis that the ETA sub‐type is the receptor that must be blocked in humans to produce a beneficial vasodilatation in pathophysiological conditions where there is an increase in peptide concentration or receptor density.
Effects of suramin on contractions of the guinea‐pig vas deferens induced by analogues of adenosine 5′‐triphosphate
Authors: Bailey S.J. , Hourani S.M.O. 
Published: July 2012

1 Adenosine 5′‐triphosphate (ATP) and some of its analogues contract the guinea‐pig vas deferens, acting via receptors which have been classified as P2X‐purinoceptors. We have recently shown, however, that the effects of ATP are enhanced, rather than inhibited, by the non‐selective P2 antagonist, suramin, and that this enhancement could not easily be explained in terms of inhibition by suramin of the breakdown of ATP. We therefore investigated the effects of suramin on contractions induced by ATP analogues, to define the structure‐activity relationships of the suramin‐resistant response.2 In the absence of suramin, the order of potency for ATP analogues was adenosine 5′‐(α,β‐methylene)triphosphonate (AMPCPP) = P1,P5‐diadenosine pentaphosphate (Ap5A) = adenosine 5′‐tetraphosphate (Ap4) > adenosine 5′‐O‐(3‐thiotriphosphate) (ATPγS) = adenylyl 5′‐(β,γ‐methylene) diphosphonate (AMPPCP)>P1,P5‐diadenosine tetraphosphate (Ap4A) > adenosine 5′‐O‐(2‐thiodiphos‐phate) (ADPβS)>2‐methylthioadenosine 5′‐triphosphate (MeSATP) ≥ ATP > adenosine 5′‐diphosphate (ADP). This is generally in agreement with previously reported structure‐activity relationships in this tissue.3 In the presence of suramin (1 mm), responses to Ap5A, Ap4A, AMPPCP, ADPβS and ADP were abolished or greatly reduced, and contractions induced by AMPCPP, Ap4 and ATPγS were inhibited. Contractions induced by MeSATP however, like those induced by ATP itself, were not reduced, but at concentrations above 100 μm were enhanced. In the presence of suramin (1 mm) the order of potency of analogues was therefore AMPCPP = Ap4 > ATP = MeSATP > ATPγS, with all other analogues tested being essentially inactive at concentrations up to 500 μm.4 Contractile responses of the vas deferens to transmural nerve stimulation (1–50 Hz) in the presence of the α‐adrenoceptor antagonist, phentolamine (10 μm), were abolished by suramin (1 mm). This is in agreement with previous reports that suramin inhibits the excitatory junction potential, a response thought to be mediated by P2 purinoceptors. It is however hard to reconcile the evidence implicating ATP as the non‐adrenergic transmitter responsible for this response with the failure of suramin to inhibit the contractions induced by ATP itself while abolishing nerve‐mediated contractions.5 In conclusion, these results confirm our previous findings of a suramin‐resistant component to the ATP‐induced contraction in the guinea‐pig vas deferens, and show that the structure‐activity relationships of this response are not identical to those of any known P2‐purinoceptor subclass. Although the inhibition by suramin of the breakdown of ATP may contribute to the suramin‐resistance of some of the ATP analogues, it does not appear to provide the full explanation.
Rapid, agonist‐induced desensitization of α2‐autoreceptors modulating transmitter release
Authors: Boehm Stefan , Huck Sigismund , Schwarz Karin , Agneter Ernst , Drobny Helmut , Singer Erast A. 
Published: July 2012

1 The release of previously incorporated [3H]‐noradrenaline was investigated in cultures of dissociated chick or rat sympathetic neurones and in cerebrocortical slices from neonatal or adult rats. Noradrenaline, in the presence of 10 μmol l−1 of the uptake inhibitor, cocaine, or the selective α2‐adrenoceptor agonist, 5‐bromo‐N‐(4,5‐dihydro‐1H‐imidazol‐2‐yl)‐6‐quinoxalinamine (UK 14,304), was applied for different periods of time in order to detect a possible time‐dependence of the α2‐adrenoceptor‐mediated inhibition of electrically evoked tritium outflow.2 In chick sympathetic neurones, stimulation‐evoked overflow was reduced to 30%, 42%, or 56% of control when noradrenaline (1 μmol l−1) was present for 2, 8, or 16 min, respectively. Likewise, UK 14,304 (1 μmol l−1) present for these periods of time reduced 3H overflow to 35%, 51%, and 53% of control, respectively. Addition of 1 nmol l−1 to 10 μmol l−1 UK 14,304 for either 2 or 16 min did not produce significantly different IC50 values, but the inhibitory effects were smaller with 16 min as compared to 2 min exposure at concentrations ≥ 10 nmol l−1.3 In rat sympathetic neurones, noradrenaline (100 nmol l−1) reduced stimulation‐evoked overflow to 33%, 56%, or 57% of control, when present for 2, 8, or 16 min, respectively. Addition of UK 14,304 (1 μmol l−1) for these periods of time caused inhibition to 11%, 41%, and 46% of control. Applying UK 14,304 for either 2 or 16 min did not result in significantly different IC50 values, but the inhibition induced by 16 min as compared to 2 min exposure was smaller at concentrations ≥ 10 nmol l−1.4 In cerebrocortical slices from either neonatal or adult rats, exposure to 0.1 to 1.0 μmol l−1 UK 14,304 for 16 min never caused a smaller inhibition than a corresponding 3 min exposure, although various experimental conditions were investigated.5 The results demonstrate that α2‐adrenoceptors which regulate noradrenaline release from sympathetic neurones undergo agonist‐induced desensitization within minutes. Such rapid desensitization of α2‐autoreceptors was not detected in brain slice preparations.
A novel enhancing effect of clofilium on transient outward‐type cloned cardiac K+ channel currents
Authors: Kobayashi Tsutomu , Mikala Gabor , Yatani Atsuko 
Published: July 2012

1 The antiarrythmic drug, clofilium, has been shown to block several types of K+ channel currents. To investigate the effects of clofilium on the transient outward K+ current (Ito), a cloned Ito‐type cardiac K+ channel (RHK1) was expressed in Xenopus oocytes and the drug effects were examined on whole cell currents.2 Extracellular application of clofilium slightly inhibited the current at + 60 mV from a holding potential of −80 mV. However, it unexpectedly enhanced the current from a holding potential of −60 mV in a dose‐dependent manner (219 ± 39% of control at 100 μm).3 This enhancement is probably due to an increase in the ratio of channels in the resting state during steady depolarization, since clofilium shifted the inactivation curve in the depolarizing direction.4 LY97119, a tertiary ammonium analogue of clofilium, did not exhibit this enhancing effect but only inhibited the current.5 Clofilium may be useful for the study of channel inactivation because this type of phenomenon has not been reported for any other drug.
Delayed circulatory failure due to the induction of nitric oxide synthase by lipoteichoic acid from Staphylococcus aureus in anaesthetized rats
Authors: De Kimpe Sjef J. , Hunter Melanie L. , Bryant Clare E. , Thiemermann Christoph , Vane John R. 
Published: July 2012

1 This study investigates the effect of lipoteichoic acid (LTA) from the cell wall of Staphylococcus aureus, a micro‐organism without endotoxin, on haemodynamics and induction of nitric oxide synthase (iNOS) in the anaesthetized rat.2 Intravenous injection of LTA (10 mg kg−1) resulted in a decrease in blood pressure from 123 ± 1 mmHg to 83 ± 7 mmHg after 270 min (P< 0.001) and a reduction of the pressor response to noradrenaline (1 μg kg−1) from 33 ± 1 mmHg.min to 23 ± 3 mmHg.mm after 270 min (P>0.05).3 The delayed circulatory failure (hypotension and vascular hyporeactivity) caused by LTA was prevented by pretreatment of rats with dexamethasone (10 mg kg−1, 60 min prior to LTA) or the nitric oxide synthase inhibitor NG‐monomethyl‐l‐arginine (l‐NMMA, 10 mg kg−1h−1, i.v. infusion starting 30 min prior to LTA).4 In contrast, treatment of rats with polymyxin B (0.05 mg kg−1), an agent which binds endotoxin (lipopolysaccharides, LPS), did not affect the delayed circulatory failure caused by LTA. Polymyxin B, however, attenuated the hypotension and vascular hyporeactivity to noradrenaline afforded by endotoxaemia (2 mg kg−1 LPS, i.v.) for 270 min.5 The delayed circulatory failure caused by LTA was associated with a time‐dependent increase in (i) the expression of iNOS protein in the lung (Western blot analysis), and (ii) iNOS activity. This increase in iNOS protein and activity was prevented by pretreatment of LTA‐rats with dexamethasone (10 mg kg−1).6 Intravenous injection of LTA resulted in an increase in serum tumour necrosis factor (TNF)‐α (maximum at 90 min after LTA), which was attenuated by pretreatment of rats with dexamethasone (10 mg kg−1, 60 min prior to LTA). The magnitude of the rise in TNF‐α caused by LTA was similar to the one elicited by LPS (10 mg kg−1, i.v.).7 Thus, an enhanced formation of nitric oxide following the induction of iNOS contributes importantly to the delayed vascular failure (hypotension and vascular hyporeactivity) caused by LTA in the anaesthetized rat. We suggest that the endogenous release of TNF‐α contributes to the induction of iNOS caused by LTA in vivo.