bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of GABA and various allosteric ligands on TBPS binding to cloned rat GABAA receptor subtypes
Authors: Im Wha Bin , Pregenzer Jeffrey F. , Thomsen Darrel R. 
Published: July 2012

[35S]t‐butylbicyclophosphorothionate (TBPS) is a high affinity ligand for the picrotoxin site of GABAA receptors. Here we examined TBPS binding to the cloned receptors made of α1, α3 or α6 in combination with β2 or β2 and γ2 subunits, in the presence of GABA and several allosteric ligands (diazepam, methyl 6,7‐dimethoxy‐4‐methyl‐β‐carboline‐3‐carboxylate (DMCM), 3α,21‐dihydroxy‐5α‐pregnan‐20‐one (5α‐THDOC), pentobarbitone and Zn). The cloned receptors were transiently expressed in SF‐9 insect cells by infecting with recombinant baculoviruses.
In αβ subtypes, GABA at nanomolar concentrations enhanced TBPS binding but inhibited binding at micromolar concentrations. Half maximal GABA concentrations for enhancement or inhibition of TBPS binding were correlated with high and low affinity GABA binding sites, respectively, in individual subtypes. The maximal enhancement of binding also varied according to the α isoform (α3β2>>α1β2>α6β2). In αβγ subtypes, TBPS binding was unaffected by GABA at nanomolar concentrations, but was inhibited by GABA at micromolar concentrations. Addition of γ2 thus appeared to abolish conformational coupling between high affinity GABA sites and TBPS sites, and also altered low affinity GABA sites; in particular, the half maximal GABA concentration for inhibition of TBPS binding changed from > 100 (α6β2) to 1 μm (α6β2γ2).
Allosteric ligands also altered TBPS binding to sensitive GABAA receptor subtypes. For instance, diazepam only in the α1β2γ2 and α3β2γ2 subtypes, and 5α‐THDOC in all the subtypes enhanced TBPS binding in the absence of GABA, and intensified the inhibitory effect of GABA. Pentobarbitone exhibited only the latter effect in all the subtypes we examined.
DMCM and Zn, inhibitors of GABA‐induced Cl currents in αβγ and αβ subtypes, respectively, produced opposite effects to agonists, decreasing TBPS binding in the absence of GABA and attenuating (or eliminating in the case of Zn) the inhibitory effect of GABA on TBPS binding.
These results show that GABA binding sites and their conformational coupling with TBPS sites are differentially affected by the α isoform (particularly α6 as compared to α1 or α3) and by quaternary interactions involving the γ2 subunit. Moreover, changes in TBPS binding by allosteric ligands include not only direct (allosteric) effects on TBPS sites but also indirect effects via GABA sites, and are consistent with their known subtype selectivity and functionality from previous studies.
Antiarrhythmic effects of BN‐063, a newly synthesized adenosine A1 agonist, on myocardial ischaemia in rats
Authors: Lee Yen‐Mei , Chern Ji‐Wang , Yen Mao‐Hsiung 
Published: July 2012

It has been shown that adenosine is able to reduce the severity of arrhythmias induced by myocardial ischaemia. In isolated preparations, the antiarrhythmic effect of adenosine on ventricular myocardium is known to antagonize the catecholamine‐induced stimulation of intracellular cyclic AMP production, an effect mediated via adenosine A1 receptors.
The aim of this study was to evaluate the antiarrhythmic effect of BN‐063 (1‐cyclo‐propylisoguanosine), a newly synthesized selective adenosine A1 agonist, on ventricular arrhythmias in rats.
Arrhythmias were induced by left coronary artery ligation or by administration of isoprenaline (7 mg kg−1) subcutaneously. Pretreatment with BN‐063 (0.25, 0.5 and 1.0 mg kg−1) 10 min prior to occlusion significantly delayed the onset of ventricular arrhythmias, reduced the total number of ventricular premature contraction (VPC) and ventricular tachycardia (VT), decreased the incidence of VT and ventricular fibrillation (VF) and mortality during the first 30 min following left coronary artery ligation. In contrast, pretreatment with 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX), an adenosine A1 antagonist, was arrhythmogenic during the ischaemic period. The rate‐pressure product, an index for indirect measurement of myocardial oxygen consumption, was also significantly reduced by BN‐063 during ligation time.
The incidence of VT, VF and mortality was also significantly reduced when BN‐063 was administered after left coronary artery ligation.
BN‐063 converted the VF induced by isoprenaline to normal sinus rhythm and improved the survival rate.
It is concluded that, through activation of adenosine A1 receptors, BN‐063 can suppress ventricular arrhythmias induced by myocardial ischaemia and catecholamines. The antiarrhythmic actions of BN‐063 may be mediated by reducing heart rate and antagonizing the stimulatory effects of catecholamine in myocardial ischaemia.
Novel histamine H3 receptor antagonists: affinities in an H3 receptor binding assay and potencies in two functional H3 receptor models
Authors: Schlicker E. , Kathmann M. , Reidemeister S. , Stark H. , Schunack W. 
Published: July 2012

We determined the affinities of ten novel H3 receptor antagonists in an H3 receptor binding assay and their potencies in two functional H3 receptor models. The novel compounds differ from histamine in that the aminoethyl side chain is replaced by a propyl or butyl chain linked to a polar group (amide, thioamide, ester, guanidine, guanidine ester or urea) which, in turn, is connected to a hexocyclic ring or to an alicyclic ring containing an alkyl residue.
The specific binding of [3H]‐Nα‐methylhistamine to rat brain cortex membranes was monophasically displaced by each of the ten compounds at pKi values ranging from 7.56 to 8.68.
Inhibition by histamine of the electrically evoked tritium overflow from mouse brain cortex slices preincubated with [3H]‐noradrenaline was antagonized by the ten compounds and the concentration‐response curve was shifted to the right with apparent pA2 values ranging from 7.07 to 9.20.
The electrically induced contraction in guinea‐pig ileum strips (which was abolished by atropine) was inhibited by the H3 receptor agonists R‐(−)‐α‐methylhistamine (pEC50 7.76), Nα‐methylhistamine (7.90) and imetit (8.18). The concentration‐response curve of R‐(−)‐α‐methylhistamine was shifted to the right by thioperamide (apparent pA2 8.79) and by the ten novel compounds (range of pA2 values 6.64–8.81).
The affinities and potencies were compared by linear regression analysis. This analysis was extended to thioperamide, the standard H3 receptor antagonist, which is also capable of differentiating between H3A and H3B sites. Comparison of the apparent pA2 values in the two functional H3 receptor models yielded a regression coefficient of 0.77 (P < 0.02). When the pA2 of the drugs in the mouse brain cortex were compared to the pKi for H3 sites (ten novel compounds) and for H3A sites (thioperamide), a significant correlation (r = 0.87; P < 0.001) was obtained. There was, however, no significant correlation when the pKi of thioperamide for H3B sites was used instead (r = 0.52). In a similar manner, comparison of the pA2 in the guinea‐pig ileum with the pKi in the binding assay yielded a significant correlation (r = 0.70, P < 0.05) only when the pKi of thioperamide for H3A sites was used but not when its pKi for H3B sites was considered (r = 0.17, NS).
On the basis of these results, structure‐activity relationships for the novel H3 receptor antagonists, and the nature of the H3 receptors in the guinea‐pig ileum and mouse brain, are considered.
Electrophysiological evidence for different release mechanism of ATP and NO as inhibitory NANC transmitters in guinea‐pig colon
Authors: Zagorodnyuk Vladimir , Maggi Carlo Alberto 
Published: July 2012

The effect of the P2‐purinoceptor antagonist, suramin, the specific N‐type voltage‐dependent calcium channel blocker, ω‐conotoxin GVIA (ω‐CgTx) and the δ‐opioid receptor agonist [d‐Pen2, d‐Pen5] enkephalin (DPDPE) on the apamin‐sensitive and apamin‐resistant inhibitory junction potentials (i.j.ps) produced by electrical field stimulation (EFS) were investigated by means of a sucrose‐gap technique in the circular muscle of the guinea‐pig colon.
After incubation of muscle strips in either atropine (1 μm), guanethidine (3 μm) and NG‐nitro‐l‐arginine (l‐NOARG, 30 μm) or atropine, guanethidine and apamin (0.3 μm), the addition of the NK1 receptor antagonist, SR 140,333 (1 μm) abolished the non‐adrenergic, non‐cholinergic (NANC) excitatory junction potential (e.j.p.) and unmasked a pure apamin‐sensitive i.j.p. (in the presence of l‐NOARG) or a pure apamin‐resistant i.j.p. (in the presence of apamin). Both types of i.j.p. were abolished by tetrodotoxin.
Suramin (30–300 μm) concentration‐dependently inhibited the apamin‐sensitive i.j.p., while the apamin‐resistant i.j.p. was not significantly affected by suramin (up to 300 μm). l‐NOARG (30 μm) markedly reduced the apamin‐resistant i.j.p.
The δ‐opioid receptor agonist, DPDPE (0.03–3 μm) concentration‐dependently reduced the apamin‐sensitive i.j.p., while leaving the apamin‐resistant i.j.p. unaffected. Naloxone (1 μm) prevented the i.j.p. inhibition evoked by DPDPE (0.3 μm).
ω‐CgTx (0.3 μm) markedly reduced the apamin‐sensitive but not the apamin‐resistant i.j.p. The application of DPDPE (3 μm), after development of a steady state inhibitory effect by ω‐CgTx, evoked further inhibition of the apamin‐sensitive i.j.p., similar to the effect produced by DPDPE alone. The L‐type calcium channel blocker, nifedipine (1 μm) did not significantly affect either the apamin‐sensitive or the apamin‐resistant i.j.ps.
These findings support the purinergic origin of the fast, apamin‐sensitive i.j.p. produced by EFS in the circular muscle of the guinea‐pig colon and strongly suggest that the apamin‐sensitive and the apamin‐resistant components of the evoked i.j.p. utilize different mechanisms for the secretion of the NANC transmitters, ATP and NO, respectively.
Investigation of the role of 5‐HT3 and 5‐HT4 receptors in ascending and descending reflexes to the circular muscle of guinea‐pig small intestine
Authors: Yuan S.Y. , Bornstein J.C. , Furness J.B. 
Published: July 2012

The present study was undertaken to ascertain whether 5‐hydroxytryptamine (5‐HT) acting at either 5‐HT3 or 5‐HT4 receptors plays a significant role in motility reflexes in the guinea‐pig small intestine.
An isolated segment of small intestine was opened along its mesenteric border and pinned, mucosa uppermost, in a three chambered organ bath so that the oral, middle and anal regions of a single preparation could be separately superfused.
Conventional intracellular recording methods were used to monitor the responses of the circular muscle in the oral or the anal end chambers when distension was applied in either of the other two chambers or the mucosal villi were compressed in the middle chamber. Drugs were added to the middle chamber.
5‐HT3 receptor antagonists (tropisetron, 0.1–10 μm; granisetron, 1 μm and BRL 46470, 1 μm) depressed the ascending excitatory reflex evoked by these stimuli but had no effect on the descending inhibitory reflex. The depression of the excitatory reflex was observed whether the reflex was evoked from the chamber containing the drug or was simply conducted, via interneurones, through this chamber.
The 5‐HT4 receptor antagonist, SDZ 205–557 (1 μm), had no significant effect on either the ascending or descending reflex pathways. However, 5‐HT4 receptors were present as cisapride (0.1 μm) significantly enhanced the ascending excitation without affecting the descending inhibition. This effect of cisapride was converted to a significant depression of the ascending reflex by SDZ 205–557.
The results suggest that 5‐HT3, but not 5‐HT4, receptors play an important role in the ascending excitatory reflex and that these receptors may be on interneurones in the reflex pathway.
Role of cyclic AMP‐induced Cl conductance in aqueous humour formation by the dog ciliary epithelium
Authors: Chen Shan , Inoue Ryuji , Inomata Hajime , Ito Yushi 
Published: July 2012

The effects of isoprenaline, a forskolin derivative NKH‐477, and dibutyryl cyclic AMP (db cyclic AMP) on the membrane potential, conductance and cell volume of the dog non‐pigmented ciliary epithelium (NPE) were investigated by intracellular potential recording, nystatin‐perforated patch clamp technique and videomicroscopic cytometry.
The resting membrane potential of NPE was about − 70 mV in physiological saline and was depolarized by isoprenaline in a dose‐dependent manner with an ED50 of about 3 nM. This depolarization was competitively antagonized by the β‐adrenoceptor antagonist, timolol (pA2 = ca. 9) and almost completely blocked by the Cl transport blocker, DIDS.
In single dissociated NPE cells, 10 μm isoprenaline induced an inward current and caused a concomitant decrease in cell volume. The reversal potential measurement indicated that this inward current was carried mainly by Cl ion. DIDS (10 μm) abolished both the current and cell volume decrease.
NKH‐477 (10 μm) or db cyclic AMP (1 mM) also induced an inward current together with a cell volume decrease, the properties of which were similar to those caused by isoprenaline.
These results suggest that β‐adrenoceptor stimulation in NPE leads to an increased rate of aqueous humour production by increasing Cl− efflux via an elevation of cyclic AMP and this effect is efficiently blocked by timolol.
Effects of bradykinin B2 receptor antagonism on the hypotensive effects of ACE inhibition
Authors: Bouaziz Herve , Joulin Yves , Safar Michel , Benetos Athanase 
Published: July 2012

The aim of this study was to determine the participation of endogenous bradykinin (BK) in the antihypertensive effects of the angiotensin converting enzyme inhibitor (ACEI), perindoprilat, in the spontaneously hypertensive rat (SHR) on different salt diets.
Conscious SHRs receiving either a low or a high NaCl diet were used in order to evaluate the respective roles of angiotensin II suppression and bradykinin stimulation in the acute hypotensive effects of perindoprilat. Two different B2 receptor antagonists (B 4146 and Hoe 140) were used after bolus administration of 7 mg kg−1 of the ACEI, perindoprilat. In separate animals, Hoe 140 was administered before the injection of perindoprilat. In other experiments, the effects of Hoe 140 on the hypotensive effects of the calcium antagonist, nicardipine, were tested.
The different NaCl diets had no effect on baseline blood pressure. Hoe 140 injection before ACE inhibition did not modify blood pressure. Perindoprilat caused more marked hypotension in the low salt‐fed rats than in the high salt animals (P < 0.01). Administration of Hoe 140 or B4146 after perindoprilat significantly reduced the antihypertensive effects of perindoprilat in the different groups, but this effect was more pronounced in high salt‐fed rats. However, in SHRs receiving Hoe 140 before perindoprilat, the antihypertensive effect of perindoprilat was completely abolished in both high or low salt diet rats. In separate experiments we confirmed that Hoe 140 did not affect the hypotensive efficacy of the calcium antagonist, nicardipine.
Our study shows that inhibition of endogenous bradykinin degradation participates in the acute antihypertensive effects of perindoprilat in SHRs. The role of bradykinin is more pronounced following exposure to a high salt diet i.e., when the renin‐angiotensin system is suppressed. Blockade of bradykinin B2 receptors by Hoe 140 before administration of perindoprilat completely abolished the hypotensive effect of perindoprilat suggesting an increased role of bradykinin in the onset of hypotensive action of ACE inhibitors. However, the exact mechanism of this interaction remains unclear.
Role of interleukin‐5 in enhanced migration of eosinophils from airways of immunized guinea‐pigs
Authors: Coéffier Eliane , Joseph Danielle , Vargaftig B. Boris 
Published: July 2012

Platelet activating factor (PAF), leukotriene B4 (LTB4) and interleukin‐5 (IL‐5) are potent chemoatt‐ractants for guinea‐pig eosinophils, which may be involved in eosinophil recruitment and up‐regulation in allergic diseases. Eosinophils from the bronchoalveolar lavage fluid (BALF) of ovalbumin‐sensitized guinea‐pigs were collected 24 h after antigen provocation and migration induced by PAF, LTB4 and rhIL‐5 was studied.
Total BALF content and distribution of eosinophils were greater in immunized, ovalbumin‐challenged guinea‐pigs (5.0 ± 0.8 × 106/guinea‐pig; 12 ± 1%) than in immunized, saline‐challenged animals (3.0 ± 0.7 × 106/guinea‐pig; 7 ± 1%).
The chemoattraction of eosinophils isolated on a metrizamide gradient was studied in micro‐Boyden chambers, results being expressed as the number of migrating cells (mean ± s.e.mean). PAF and LTB4‐induced migration of eosinophils from immunized and OA‐challenged guinea‐pigs were significantly enhanced, as compared to immunized and saline‐challenged animals (170 ± 36 vs 35 ± 9 migrating eosinophils for 10 nm PAF; 271 ± 60 vs 110 ± 19 for 1 nm LTB4).
The IL‐5 antibody TRFK‐5, in vivo, reduced eosinophil recruitment in BALF of antigen‐challenged immunized animals as well as the enhanced responsiveness of eosinophils from the challenged animals, suggesting a role for IL‐5 in the priming of eosinophils in vivo.
In contrast to TRFK‐5, nedocromil sodium reduced to a similar extent eosinophil, macrophage and lymphocyte recruitment into the BALF of antigen‐challenged, but failed to down‐regulate the enhanced responsiveness of eosinophils from the challenged animals.
The increased eosinophil content in lungs from antigen‐challenged guinea‐pigs is thus selectively reduced by the anti‐IL‐5 antibody, which also attenuates the concomitant enhancement of the eosinophil responsiveness, supporting the concept that IL‐5 is essential for recruitment and priming of eosinophils in vivo. In contrast, nedocromil sodium reduced non‐selectively the total cell recruitment to the airways, but failed to attenuate the enhanced responsiveness of those eosinophils which migrated, indicating that its effects involve a different target.
Dual effects of tetrandrine on cytosolic calcium in human leukaemic HL‐60 cells: intracellular calcium release and calcium entry blockade
Authors: Leung Yuk‐Man , Kwan Chiu‐Yin , Loh Tatt‐Tuck 
Published: July 2012

Tetrandrine (TET, a Ca2+ antagonist of Chinese herbal origin) and thapsigargin (TSG, an endoplasmic reticulum Ca2+ pump inhibitor) concentration‐dependently mobilized Ca2+ from intracellular stores of HL‐60 cells, with EC50 values of 20 μm and 0.8 nm, respectively. After intracellular Ca2+ release by 30 nm TSG, there was no more discharge of Ca2+ by TET (100 μm), and vice versa.
Pretreatments with 100 nm rauwolscine (α2‐adrenoceptor antagonist), 100 nm prazosin (α1‐adreno‐ceptor antagonist), 10 nm phorbol myristate acetate (PMA, a protein kinase C activator) or 100 nm staurosporine (a protein kinase C inhibitor) had no effect on 100 μm TET‐induced intracellular Ca2+ release.
After intracellular Ca2+ release by 30 nm TSG in Ca2+‐free medium, readmission of Ca2+ caused a substantial and sustained extracellular Ca2+ entry. The latter was almost completely inhibited by 100 μm TET (IC50 of 20 μm) added just before Ca2+ readmission. In Ca2+‐containing medium, 30 nm TSG caused a sustained phase of cytosolic Ca2+ elevation, which could be abolished by 100 μm TET. TET was also demonstrated to retard basal entry of extracellular Mn2+ and completely inhibit TSG‐stimulated extracellular Mn2+ entry.
TSG‐induced extracellular Ca2+ entry was insensitive to the L‐type Ca2+ channel blocker, nifedipine (1 μm), but was completely inhibited by the non‐selective Ca2+ channel blocker La3+ (300 μm). Depolarization with 100 mm KCl did not raise the cytosolic Ca2+ level.
These data suggest that (a) TET and TSG mobilized the same Ca2+ pool and TET‐induced intracellular Ca2+ release was independent of protein kinase C activity and a‐adrenoceptor activation, and (b) TET blocked the voltage‐insensitive Ca2+ entry pathway activated by TSG. These dual effects on HL‐60 cells were also observed with hernandezine (HER), a TET‐like compound and in another cell type, murine B lymphoma M12.4 cells.
Antagonism by (R)‐ and (S)‐trihexyphenidyl of muscarinic stimulation of adenylyl cyclase in rat olfactory bulb and inhibition in striatum and heart
Authors: Onali Pierluigi , Aasen Arne J. , Olianas Maria C. 
Published: July 2012

Activation of muscarinic receptors in rat olfactory bulb stimulates adenylyl cyclase activity. This response was competitively antagonized by the (R)‐ and (S)‐enantiomers of trihexyphenidyl with pA2 values of 8.84 and 6.09, respectively.
Similarly, in rat striatal homogenates, muscarinic inhibition of adenylyl cyclase activity was antagonized by the (R)‐ and (S)‐enantiomers with pA2 values of 8.75 and 6.12, respectively.
In contrast, in rat myocardium the muscarinic inhibition of the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) formation was more weakly antagonized by trihexyphenidyl, with a particularly marked loss (15 fold) in activity of the (R)‐enantiomer. The (R)‐ and (S)‐enantiomers had pA2 values of 7.64 and 5.72, respectively.
Each muscarinic response was completely antagonized by increasing concentrations of (R)‐trihexyphenidyl with a Hill coefficient not significantly different from unity.
The present study shows that the muscarinic receptors coupled to stimulation of adenylyl cyclase in the olfactory bulb display high stereoselectivity for the enantiomers of trihexyphenidyl. The affinities of these receptors for the antagonists are similar to those shown by the striatal receptors. This finding supports the hypothesis that both the muscarinic stimulation of adenylyl cyclase in the olfactory bulb and the muscarinic inhibition of the enzyme in striatum are mediated by activation of a receptor subtype pharmacologically equivalent to the m4 gene product. On the other hand, the weaker affinities and the lower stereoselectivity for the trihexyphenidyl enantiomers exhibited by the muscarinic inhibition of adenylyl cyclase in the heart are consistent with the involvement of M2 receptors in this response.
Agonist‐induced desensitization of histamine Hi receptor‐mediated inositol phospholipid hydrolysis in human umbilical vein endothelial cells
Authors: McCreath G. , Hall LP. , Hill S.J. 
Published: July 2012

The regulation of histamine‐induced [3H]‐inositol phosphate formation was studied in human cultured umbilical vein endothelial cells (HUVEC).
Histamine (EC50 4.8 μm) produced a 12.7 fold increase in [3H]‐inositol phosphate formation over basal levels. Prior exposure to 0.1 mm histamine (2h) produced a 78% reduction in the response to subsequent histamine (0.1 μm) challenge. The IC50 for this histamine‐induced desensitization was 0.9 μm.
The inositol phosphate response to histamine (0.1 μm) was inhibited by phorbol dibutyrate (IC50 40 nm; maximal reduction 64%). This effect was antagonized by both staurosporine (100 nm) and Ro 31–8220 (10 μm). However, the histamine‐induced desensitization of the H1‐receptor‐mediated inositol phosphate response was insensitive to the protein kinase inhibitors, staurosporine, Ro 31–8220, K252a and KN62.
Prior exposure to sodium nitroprusside (100 μm), forskolin (10 μm) or dibutyryl cyclic AMP (1 μm) had no effect upon histamine‐induced [3H]‐inositol phosphate formation.
NaF (20 μm) and thrombin (EC50 0.4 u ml−1) also induced inositol phosphate formation in HUVEC. Histamine pretreatment (0.1 mm, 10‐120min) failed to modify the inositol phosphate response to a subsequent NaF or thrombin challenge.
We conclude that the desensitization of histamine Hrreceptor‐mediated [3H]‐inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activation of protein kinase A, G, or C, or calcium calmodulin‐dependent protein kinase II.