bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of neuromuscular blockade induced by phenthonium, a quaternary derivative of (−)–hyoscyamine, in skeletal muscles
Authors: Souccar Caden , Lima‐Landman Maria Teresa R. , Ballejo Gustavo , Lapa Antonio José
Published: January 2005

The mechanisms underlying the postjunctional blockade induced by phenthonium [N‐(4‐phenyl) phenacyl 1‐hyoscyamine] were investigated in mammalian and amphibian muscles. This muscarinic antagonist was previously shown to enhance specifically the spontaneous acetylcholine (ACh) release at concentrations that blocked neuromuscular transmission.

In both rat diaphragm and frog sartorius muscles, phenthonium (Phen, 1–100 μm) depressed the muscle twitches elicited by nerve stimulation (IC50: 23 μm and 5 μm, respectively), and blocked the nerve‐evoked muscle action potential. The neuromuscular blockade was not reversed after incubation with neostigmine.

Equal concentrations of Phen decreased the rate of rise and prolonged the falling phase of the directly elicited action potential in frog sartorius muscle fibres, indicating that the drug also affects the sodium and potassium conductance.

Phen (50 and 100 μm) protected the ACh receptor against α‐bungarotoxin (BUTX) blockade in the mouse diaphragm allowing recording of endplate potentials and action potentials after 5 h wash with physiological salt solution.

Phen (10–100 μm) produced a concentration‐ and voltage‐dependent decrease of the endplate current (e.p.c.), and induced nonlinearity of the current‐voltage relationship. At high concentrations Phen also shortened the decay time constant of e.p.c (τe.p.c.) and reduced its voltage sensitivity.

At the same range of concentrations, Phen also reduced the initial rate of [125I]‐BUTX binding to junctional ACh receptors of the rat diaphragm (apparent dissociation constant = 24 μm), the relationship between the degree of inhibition and antagonist concentration being that expected for a competitive mechanism.

It is concluded that Phen affects the electrical excitability of the muscle fibre membrane, and blocks neuromuscular transmission through a mechanism that affects the agonist binding to its recognition site and ionic channel conductance of the nicotinic ACh receptor.

British Journal of Pharmacology (1998) 124, 1270–1276; doi:10.1038/sj.bjp.0701932
Opposite effects of CCKB agonists in grooming behaviour in rats: further evidence for two CCKB subsites
Authors: Ladurelle Nathalie , Sebret Angélique , Garbay Christiane , Roques Bernard P. , Daugé Valérie
Published: January 2005

The hypothesis of the existence of two CCKB receptor subsites, CCKB1 and CCKB2 corresponding probably to different coupling states of CCKB receptors, was studied by measuring grooming behaviour in rats.

The B1 receptor agonist, BC197 (300 μg kg−1, i.p.) produced a 45–50% decrease in grooming activity, which was prevented by both the CCKB receptor antagonists CI‐988 (20 μg kg−1 i.p.) and L‐365,260 (200 μg kg−1, i.p.).

In contrast, 3, 10 and 30 μg kg−1, i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150–190%). This effect was prevented by previous injection of 75 μg kg−1 of L‐365,260 while higher doses (200 μg kg−1, i.p.) produced only a partial antagonism. Moreover, CI‐988 (20 μg kg−1, i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 μg kg−1 of CI‐988 tended to suppress the increase of grooming induced by BC264.

The effects of BC264 were prevented by the D1 receptor (SCH 23390) and D2 receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems.

This study brings additional evidence for the existence of the two CCKB receptor subsites and suggests that particular attention should be focused on the selectivity of CCKB receptor agonists, notably to explain the fact that some compounds such as Boc‐CCK4 induce anxiogenic‐like effects while others, including BC264, are devoid of these effects.

British Journal of Pharmacology (1998) 124, 1091–1098; doi:10.1038/sj.bjp.0701933
Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats
Authors: Doong Ming‐Luen , Lu Chien‐Chen , Kau Mei‐Mei , Tsai Shiow‐Chwen , Chiao Yu‐Chung , Chen Jiann‐Jong , Yeh Jiun‐Yih , Lin Ho , Huang Seng‐Wong , Chen Tseng‐Shing , Chang Full‐Young , Wang Paulus S.
Published: January 2005

The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats.

Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine.

Plasma CCK levels were increased dose‐dependently by amphetamine.

Proglumide, a CCK receptor antagonist, prevented amphetamine‐induced inhibition of gastric emptying and the decrease in GI transit in male rats.

The selective CCKA receptor antagonist, lorglumide, dose‐dependently attenuated the amphetamine‐induced inhibition of gastric emptying in male rats. In contrast, the selective CCKB receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying.

Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats.

These results suggest that amphetamine‐induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.

British Journal of Pharmacology (1998) 124, 1123–1130; doi:10.1038/sj.bjp.0701937
The nonpeptide B2 receptor antagonist FR173657: inhibition of effects of bradykinin related to its role in nociception
Authors: Griesbacher Thomas , Amann Rainer , Sametz Wolfgang , Diethart Sabine , Juan Heinz
Published: January 2005

The nonpeptide bradykinin B2 receptor antagonist, FR173657 ((E)‐3‐(6‐acetamido‐3‐pyridyl)‐N‐[N‐(2, 4‐dichloro‐3‐[(2‐methyl‐8‐quinolinyl) oxymethyl] phenyl]‐N‐methylaminocarbonylmethyl] acrylamide), was tested in models involving bradykinin‐induced activation of primary afferent neurones in vitro and in vivo.

Bradykinin‐induced contractions of the rabbit isolated iris sphincter muscle mediated by tachykinin release from trigeminal afferent neurones were inhibited in a non‐competitive manner by FR173657. A pKB value of 7.9 was calculated. Effects of substance P were unaffected by FR173657.

Nociceptive behavioural responses following intraplantar injection of bradykinin in unanaesthetized rats were reduced by 0.3 μmol kg−1 FR173657 s.c. (P<0.05), and completely abolished by 3 μmol kg−1 (P<0.05). Peroral administration of 5 μmol kg−1 FR173657 abolished the bradykinin effects (P<0.05); lower doses had no significant effect.

Shortening by intraplantar injection of bradykinin of the paw withdrawal latency in response to radiant heat was abolished by 3 μmol kg−1 FR173657 s.c. (P<0.05), while 300 nmol kg−1 had an intermediate effect. Hyperalgesia induced by prostaglandin E2 remained unaffected by FR173657.

Blood pressure reflexes following i.p. instillation of bradykinin in anaesthetized rats were inhibited by FR173657 s.c. with an ID50 of 1.1 μmol kg−1, while the peptidic B2 antagonist icatibant (Hoe‐140; d‐Arg0‐[Hyp3, Thi5, d‐Tic7, Oic8]‐bradykinin) caused inhibition at significantly lower doses (ID50 8.5 nmol kg−1 P<0.001). Responses to hydrochloric acid i.p. remained unaffected by FR173657.

FR173657 or similar nonpeptide compounds may be useful for the development of drugs for diseases involving pain induced by the release of endogenous kinins, i.e. especially in acute inflammatory conditions.

British Journal of Pharmacology (1998) 124, 1328–1334; doi:10.1038/sj.bjp.0701938
Culture substrate‐specific expression of P2Y2 receptors in distal lung epithelial cells isolated from foetal rats
Authors: Clunes M T. , Collett A , Baines D L. , Bovell D L. , Murphie H , Inglis S K. , McAlroy H L. , Olver R E. , Wilson S M.
Published: January 2005

ATP and UTP did not evoke [Ca2+]i signals in rat foetal lung epithelial cells grown on glass but elicited clear responses in cells grown into functionally polarised epithelia on permeable supports. Moreover, P2Y2 receptor mRNA could not be detected in cells on glass by the polymerase chain reaction but this mRNA species was clearly expressed by polarised cells. P2Y2 receptor expression thus appears to be a feature of the polarised phenotype.
Development of endothelin receptors in perinatal rabbit pulmonary resistance arteries
Authors: Docherty Cheryl , MacLean Margaret R.
Published: January 2005

Contractile responses to endothelin‐1 (ET‐1) and sarafotoxin S6c (S6c) were studied in pulmonary resistance arteries (∼320 μm i.d.) from fetal, 0–24 h, 4 day and 7 day rabbits. The effects of the ETA‐selective antagonist FR139317, the selective ETB receptor antagonist BQ‐788 and the non‐selective ETA/ETB receptor antagonist SB 209670, on these responses, were determined. Acetylcholine‐induced vasodilation and noradrenaline‐evoked contractions were also examined.

ET‐1 potency was in the following order (pEC50 values): fetal (8.7) = 0–24 h (8.8) = 4 day (8.6) > 7 day (8.0). The order of potency for S6c was 7 days (11.1) = 4 days (10.8) >0–24 h (9.7) > fetal (8.6). Hence, S6c and ET‐1 were equipotent in the fetus but S6c was increasingly more potent than ET‐1 with increasing age, being some 1000 times more potent by 7 days. By 7 days, responses to ET‐1 were also resistant to both FR139317 and BQ‐788. FR139317 inhibited responses to ET‐1 in vessels from 0–24 h and 4 day, but not fetal, rabbits (pKb: 6.4 in 4 day rabbits). BQ‐788 inhibited responses to ET‐1 at all age points except for 7 days (pKb: 6.7 at 0–24 h; 6.2 at 4 days). BQ‐788 inhibited responses to S6c at all age points (pKb: 8.5 at 4 days). SB 209670 inhibited responses to ET‐1 and S6c at 0–24 h and 4 days (pKb for ET‐1: 8.3 and 8.0 respectively; pKb for S6c: 9.2 and 10.2 respectively).

Acetylcholine (1 μm) induced vasodilation at all age points (inhibited by 100 μm l‐Nω‐nitroarginine methylester) although the degree of vasodilation was significantly reduced (∼75%) at 0–24 h. Noradrenaline induced contraction at all age points except 7 days and its response was significantly enhanced at 0–24 h.

Over the first week of life, the potency of S6c increases whilst that to ET‐1 decreases suggesting differential development of responses to ET‐1 and S6c and heterogeneity of ETA‐ or ‘ETB‐like’ receptor‐mediated responses. There is no synergism between ETA and ETB receptors at birth but this is established by 7 days. Immediately after birth rabbit Pulmonary Resistance Arteries are hyperresponsive to ET‐1 and noradrenaline but exhibit impaired nitric‐oxide dependent vasodilation.

British Journal of Pharmacology (1998) 124, 1165–1174; doi:10.1038/sj.bjp.0701950
Effects of the neuroprotectant lubeluzole on the cytotoxic actions of veratridine, barium, ouabain and 6‐hydroxydopamine in chromaffin cells
Authors: Cano‐Abad María F. , López Manuela G. , Hernández‐Guijo Jesús M. , Zapater Pedro , Gandía Luis , Sánchez‐García Pedro , García Antonio G.
Published: January 2005

Incubation of bovine adrenal chromaffin cells with veratridine (10–100 μm) during 24 h, caused a concentration‐dependent release of the cytosolic lactate dehydrogenase (LDH) into the bathing medium, an indicator of cell death. Lubeluzole or its R(−) enantiomer, R91154, did not enhance LDH release. Both lubeluzole and R91154 (0.3–10 μm) decreased the veratridine‐induced LDH release.

Penfluridol did not increase LDH release at concentrations 0.003–1 μm; 3–10 μm increased LDH release to 50–60%, after 24 h exposure. Penfluridol (0.03–0.3 μm) did not protect against the cytotoxic effects of veratridine; at 1 μm, 15% protection was produced. Higher concentrations (3–10 μm) enhanced the cytotoxic effects of veratridine.

Ba2+ ions caused a concentration‐dependent increase of LDH release. This cytotoxic effect was partially prevented by 3 μm lubeluzole and fully counteracted by 1 μm penfluridol. R91154 was less potent than lubeluzole and only protected against the lesion induced by 0.5 mm Ba2+.

Ouabain (10 μm during 24 h) increased LDH release to about 30%. Both lubeluzole (0.3–10 μm) and the lower concentrations of penfluridol (0.003–0.3 μm) prevented the ouabain cytotoxic effects. At higher concentrations (3 μm), penfluridol increased drastically the ouabain cytotoxic effects.

6‐Hydroxydopamine (6‐OHDA) caused significant cytotoxic effects at 30 and 100 μm. Lubeluzole (3–10 μm) or penfluridol (0.03–0.3 μm) had no cytoprotective effects against 6‐OHDA.

Lubeluzole (3 μm), R91154 (3 μm) and penfluridol (1 μm) blocked the current through Na+ channels in voltage‐clamped chromaffin cells (INa) by around 20–30%. Ca2+ current through Ca2+ channels (ICa) was inhibited 57% by lubeluzole and R91154 and 50% by penfluridol. The effects of penfluridol were not washed out, but those of lubeluzole and R91154 were readily reversible.

Lubeluzole (3 μm) induced reversible blockade of the oscillations of the cytosolic Ca2+, [Ca2+]i, in fura‐2‐loaded cells exposed to 30 or 100 μm veratridine. Penfluridol (1 μm) inhibited those oscillations in an irreversible manner.

The results suggest that lubeluzole and its R‐isomer caused cytoprotection against veratridine cell damage, by blocking the veratridine stimulated Na+ and Ca2+ entry, as well as the [Ca2+]i oscillations. The Ba2+ and ouabain cytotoxic effects were prevented more efficiently by penfluridol, likely by blocking the plasmalemmal Na+/Ca2+ exchanger. It remains dubious whether these findings are relevant to the reported neuroprotective action of lubeluzole in stroke; the doubt rests in the stereoselective protecting effects of lubeluzole in in vivo stroke models, as opposed to its lack of stereoselectivity in the in vitro model reported here.

British Journal of Pharmacology (1998) 124, 1187–1196; doi:10.1038/sj.bjp.0701955
The effects of brucine and alcuronium on the inhibition of [3H]acetylcholine release from rat striatum by muscarinic receptor agonists
Authors: Doležal Vladimír , Tuček Stanislav
Published: January 2005

Radioligand binding experiments indicate that the affinity of muscarinic receptors for their agonists may be enhanced by allosteric modulators. We have now investigated if brucine can enhance the inhibitory effects of muscarinic receptor agonists on the electrically evoked release of [3H]acetylcholine ([3H]ACh) from superfused slices of rat striatum.

The evoked release of [3H]ACh was inhibited by all agonists tested (i.e., furmethide, oxotremorine‐M, bethanechol and oxotremorine).

Brucine enhanced the inhibitory effects of furmethide, oxotremorine‐M and bethanechol on the evoked [3H]ACh release without altering the inhibitory effect of oxotremorine.

Alcuronium was applied for comparison and found to diminish the inhibitory effect of furmethide on the evoked [3H]ACh release.

The results demonstrate that it is possible both to enhance and diminish the functional effects of muscarinic receptor agonists by allosteric modulators.

The direction of the observed effects of brucine and alcuronium on [3H]ACh release fully agrees with the effects of these modulators on the affinities of human M4 receptors for furmethide, oxotremorine‐M, bethanechol and oxotremorine, as described by Jakubík et al. (1997). This supports the view that the presynaptic muscarinic receptors responsible for the autoinhibition of ACh release in rat striatum belong to the M4 muscarinic receptor subtype.

British Journal of Pharmacology (1998) 124, 1213–1218; doi:10.1038/sj.bjp.0701966
Modulation of relaxation to levcromakalim by s‐nitroso‐n‐acetylpenicillamine (SNAP) and 8‐bromo cyclic GMP in the rat isolated mesenteric artery
Authors: White Richard , Hiley C. Robin
Published: January 2005

Levcromakalim caused concentration‐dependent relaxations of methoxamine‐induced tone in both endothelium‐denuded and intact vessels. Its potency was reduced by the nitric oxide donor, S‐nitroso‐N‐acetylpenicillamine (SNAP; 0.1 μm or 1 μm) in both denuded and intact vessels. The maximal relaxation (Rmax) was reduced only in denuded vessels.

SNAP was more potent in endothelium‐denuded than intact vessels but there were no differences in Rmax. Glibenclamide (10 μm) did not affect relaxation to SNAP in endothelium‐denuded or intact vessels.

The soluble guanylyl cyclase inhibitor, 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ, 10 μm) increased the potency and Rmax of levcromakalim in endothelium‐intact vessels. ODQ had no effect in denuded vessels.

ODQ (10 μm) reduced the vasorelaxant potency of SNAP in both intact and endothelium‐denuded vessels by 190‐fold and 620‐fold, respectively.

8‐bromo cyclic GMP (10 or 30 μm) reduced both the potency and Rmax of levcromakalim in de‐endothelialized vessels, but had no effect in intact vessels although it reduced both the potency and Rmax of levcromakalim in intact vessels incubated with ODQ (10 μm).

In the presence of ODQ (10 μm), SNAP (0.1 μm or 1 μm) reduced the potency of levcromakalim in intact vessels, without altering Rmax, but had no effect in denuded vessels. SNAP (50 μm) reduced both the potency and Rmax of levcromakalim in intact and endothelium‐denuded vessels.

Therefore, although SNAP causes relaxation principally through generation of cyclic GMP, it can modulate the actions of levcromakalim through mechanisms both dependent on, and independent of, cyclic GMP; the former predominate in endothelium‐denuded vessels and the latter in intact vessels.

British Journal of Pharmacology (1998) 124, 1219–1226; doi:10.1038/sj.bjp.0701973
Potent antihyperglycaemic property of a new imidazoline derivative S‐22068 (PMS 847) in a rat model of NIDDM
Authors: Pelé‐Tounian Agnès , Wang Xuan , Rondu Frédéric , Lamouri Azzdine , Touboul Estera , Marc Sylvie , Dokhan Raymond , Pfeiffer Bruno , Manechez Dominique , Renard Pierre , Guardiola‐Lemaître Béatrice , Godfroid Jean‐Jacques , Pénicaud Luc , Ktorza Alain
Published: January 2005

Recent data suggest that some imidazoline derivatives can lower plasma glucose in experimental animal models of diabetes. We studied the activity of an imidazoline S‐22068, in rat model of non‐insulin‐dependent diabetes mellitus (NIDDM) produced with a low dose of streptozotocin (35 mg kg−1, i.v.) in the adult.

The respective increase over basal value in glucose (ΔG) and insulin (ΔI), and the rate of glucose disappearance (K), were measured during a 30 min intravenous glucose tolerance test. After an intraperitoneal injection of S‐22068 (24 mg kg−1), ΔG (mM min −1) was decreased (91.67±5.83 vs 120.5±3.65; P<0.001), whereas K was increased (1.74±0.09 vs 1.18±0.05; P<0.001). Although insulinaemia was increased at time‐point 0 of the test, ΔI was unchanged.

During oral glucose tolerance tests (OGTT), S‐22068 (24 mg kg−1, p.o.) improved glucose tolerance, and its efficiency was potentiated after chronic treatment (15 days). Basal glycaemia was unaffected by the treatment. Under the same conditions, a higher dose of S‐22068 (40 mg kg−1) further improved glucose tolerance without causing hypoglycaemia.

Binding experiments revealed that S‐22068 displays no affinity for either adrenoceptors or the two imidazoline receptors I1 or I2.

These results demonstrate that S‐22068 improves glucose tolerance without causing hypoglycaemia. Thus S‐22068 represents a new potential option in the treatment of NIDDM.

British Journal of Pharmacology (1998) 124, 1591–1596; doi:10.1038/sj.bjp.0701989
Purinoceptor activation of chloride transport in cystic fibrosis and CFTR‐transfected pancreatic cell lines
Authors: O'Reilly Catherine M , O'Farrell Anne M , Ryan Michael P
Published: January 2005

The regulation of chloride efflux from cystic fibrosis pancreatic adenocarcinoma cells (CFPAC‐1) and wild‐type CFTR‐transfected CFPAC‐1 cells (TPAC) was compared.

Forskolin (10 μM) stimulated chloride efflux from the corrected TPAC cells but not from CFPAC‐1 cells. Chloride efflux from both cell types was activated by thapsigargin (0.5 μM).

The nucleotides ATP and UTP and the non‐hydrolyzable ATP analogue, adenosine 5′‐O‐(3‐thio) triphosphate (ATPγS), stimulated chloride efflux from both cell types. None of the other P2 purinoceptor agonists investigated elicited a response. The order of potency was ATPUTPATPγS.

Adenosine (10–100 μM) activated choride efflux from the TPAC but not the CFPAC cell line with no increase in intracellular cyclic AMP. Small but statistically significant inhibitions of the adenosine‐(50 μM)‐stimulated increase in chloride efflux were elicited by the A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (CPX, 100 nM) and the A2 receptor antagonist 3,7‐dimethyl‐1‐propylargylxanthine (DMPX, 10 μM). The A2A receptor antagonist 8‐(3‐chlorostyryl)caffeine (CSC, 100 nM) had no significant effect.

These results provide evidence for the regulation of chloride efflux by P2Y2 purinoceptors in genetically‐corrected and CF pancreatic cell lines. Studies with adenosine receptor antagonists indicate some possible involvement of A1 and A2 (but not A2A) receptors in the adenosine stimulation of chloride efflux, but the relatively small effects of the inhibitors coupled with lack of increase in cyclic AMP and a response only in the CFTR‐transfected cells also suggests a possible direct effect of adenosine on CFTR.

British Journal of Pharmacology (1998) 124, 1597–1606; doi:10.1038/sj.bjp.0701990
Involvement of ETA and ETB receptors in the activation of phospholipase D by endothelins in cultured rat cortical astrocytes
Authors: Servitja Joan‐Marc , Masgrau Roser , Sarri Elisabet , Picatoste Fernando
Published: January 2005

This study was performed to characterize the receptor subtypes involved in the endothelin stimulation of phospholipase D (PLD) in rat cortical astrocytes in primary culture. PLD activity was determined by measuring the formation of [32P]phosphatidylbutanol in [32P]orthophosphate prelabelled cells stimulated in the presence of 25 mM butanol.

The agonists endothelin‐1 (ET‐1), endothelin‐3 (ET‐3), sarafotoxin 6c (S6c) and IRL 1620 elicited PLD activation in a concentration‐dependent manner. The potencies of ET‐1, ET‐3 and S6c were similar. The maximal effects evoked by the ETB‐preferring agonists, ET‐3, S6c and IRL 1620, were significantly lower than the maximal response to the non‐selective agonist ET‐1.

The response to 1 nM ET‐1 was inhibited by increasing concentrations of the ETA receptor antagonist BQ‐123 in a biphasic manner. A high potency component of the inhibition curve (24.2±3.5% of the ET‐1 response) was defined at low (up to 1 μM) concentrations of BQ‐123, yielding an estimated Ki value for BQ‐123 of 21.3±2.5 nM. In addition, the presence of 1 μM BQ‐123 significantly reduced the maximal response to ET‐1 but did not change the pD2 value.

Increasing concentrations of the ETB selective antagonist BQ‐788 inhibited the S6c response with a Ki of 17.8±0.8 nM. BQ‐788 also inhibited the effect of ET‐1, although, in this case, two components were defined, accounting for approximately 50% of the response, and showing Ki values of 20.9±5.1 nM and 439±110 nM, respectively. The ET‐1 concentration‐response curve was shifted to the right by 1 μM BQ‐788, also revealing two components. Only one of them, corresponding to 69.8±4.4% of the response, was sensitive to BQ‐788 which showed a Ki value of 28.8±8.9 nM.

Rapid desensitization was achieved by preincubation with ET‐1 or S6c. In cells pretreated with S6c neither ET‐3 nor S6c activated PLD, but ET‐1 still induced approximately 40% of the response shown by non‐desensitised cells. This remaining response was insensitive to BQ‐788, but fully inhibited by BQ‐123.

In conclusion, endothelins activate PLD in rat cortical astrocytes acting through both ETA and ETB receptors, and this response desensitizes rapidly in an apparently homologous fashion. The percentage contribution of ETA and ETB receptors to the ET‐1 response was found to be approximately 20% and 80%, respectively, when ETB receptors were not blocked, and 30–50% and 50–70%, respectively, when ETB receptors were inhibited or desensitized. These results may be relevant to the study of a possible role of PLD in the proliferative effects shown by endothelins on cultured and reactive astrocytes.

British Journal of Pharmacology (1998) 124, 1728–1734; doi:10.1038/sj.bjp.0701997
Effect of increased cardiac output on liver blood flow, oxygen exchange and metabolic rate during longterm endotoxin‐induced shock in pigs
Authors: Šantak Borislav , Radermacher Peter , Adler Jens , Iber Thomas , Rieger Karen M , Wachter Ulrich , Vogt Josef , Georgieff Michael , Träger Karl
Published: January 2005

We investigated hepatic blood flow, O2 exchange and metabolism in porcine endotoxic shock (Control, n=8; Endotoxin, n=10) with administration of hydroxyethylstarch to maintain arterial pressure (MAP)>60 mmHg.

Before and 12, 18 and 24 h after starting continuous i.v. endotoxin we measured portal venous and hepatic arterial blood flow, intracapillary haemoglobin O2 saturation (Hb‐O2%) of the liver surface and arterial, portal and hepatic venous lactate, pyruvate, glyercol and alanine concentrations. Glucose production rate was derived from the plasma isotope enrichment during infusion of [6,6‐2H2]‐glucose.

Despite a sustained 50% increase in cardiac output endotoxin caused a progressive, significant fall in MAP. Liver blood flow significantly increased, but endotoxin affected neither hepatic O2 delivery and uptake nor mean intracapillary Hb‐O2% and Hb‐O2% frequency distributions.

Endotoxin nearly doubled endogenous glucose production rate while hepatic lactate, alanine and glycerol uptake rates progressively decreased significantly. The lactate uptake rate even became negative (P<0.05 vs Control). Endotoxin caused portal and hepatic venous pH to fall significantly concomitant with significantly increased arterial, portal and hepatic venous lactate/pyruvate ratios.

During endotoxic shock increased cardiac output achieved by colloid infusion maintained elevated liver blood flow and thereby macro‐ and microcirculatory O2 supply. Glucose production rate nearly doubled with complete dissociation of hepatic uptake of glucogenic precursors and glucose release. Despite well‐preserved capillary oxygenation increased lactate/pyruvate ratios reflecting impaired cytosolic redox state suggested deranged liver energy balance, possibly due to the O2 requirements of gluconeogenesis.

British Journal of Pharmacology (1998) 124, 1689–1697; doi:10.1038/sj.bjp.0701998
Influence of chronic hypoxia on the contributions of non‐inactivating and delayed rectifier K currents to the resting potential and tone of rat pulmonary artery smooth muscle
Authors: Osipenko O. N. , Alexander D. , MacLean M. R. , Gurney A. M.
Published: January 2005

Exposing rats to chronic hypoxia increased the 4‐aminopyridine (4‐AP) sensitivity of pulmonary arteries. 1 mm 4‐AP caused smooth muscle cell depolarization and contraction in arteries from hypoxic rats, but had little effect in age‐matched controls. Chronic hypoxia downregulated delayed rectifier K+ current (IK(V)), which was nearly 50% blocked by 1 mm 4‐AP, and non‐inactivating K+ current (IK(N)), which was little affected by 1 mm 4‐AP. The results suggest that IK(N) determines resting potential in control rats and that its downregulation following hypoxia leads to depolarization, which activates IK(V) and increases its contribution to resting potential. The hypoxia‐induced increase in 4‐AP sensitivity thus reflects a switch in the major K+ current determining resting potential, from IK(N) to IK(V). This has important implications for the actions and specificity of pulmonary vasodilator drugs.

British Journal of Pharmacology (1998) 124, 1335–1337; doi:10.1038/sj.bjp.0702006
Histamine H1‐receptor‐mediated increase in the Ca2+ transient without a change in the Ca2+ current in electrically stimulated guinea‐pig atrial myocytes
Authors: Yoshimoto Kimihiro , Hattori Yuichi , Houzen Hideki , Kanno Morio , Yasuda Keishu
Published: January 2005

The effects of histamine on the intracellular Ca2+ concentration ([Ca2+]i), action potential and membrane currents were assessed in single atrial myocytes prepared from guinea‐pigs.

Histamine caused a concentration‐dependent increase in the [Ca2+]i transient in indo1/AM loaded myocytes when stimulated electrically at 0.5 Hz. However, the maximum increase in [Ca2+]i transient produced by histamine was less than 50% of that elicited by isoprenaline. The histamine‐induced increase in [Ca2+]i transient was significantly inhibited by chlorpheniramine, but not by cimetidine.

Pretreatment with nifedipine nearly completely suppressed the histamine‐induced increase in [Ca2+]i transient. Cyclopiazonic acid did not affect the histamine response.

In the whole‐cell current‐clamp mode of the patch‐clamp method, both histamine and isoprenaline prolonged action potential duration (APD) in atrial myocytes. In the presence of Co2+ or nifedipine, the isoprenaline‐induced APD prolongation was abolished and an APD shortening effect was manifested, while histamine still increased APD. The APD prolongation elicited by histamine was reversed by chlorpheniramine.

In the voltage‐clamp mode, the histamine‐sensitive membrane current was inwardly rectifying and reversed close to the calculated value of the K+ equilibrium potential. Histamine had no apparent effect on L‐type Ca2+ current, in contrast to the pronounced effect of isoprenaline.

These results indicate that in guinea‐pig atrial myocytes stimulation of H1‐receptors with histamine does not directly activate Ca2+ channels but causes an elevation of [Ca2+]i transient by increasing Ca2+ influx through the channels during the prolonged repolarization of action potentials resulting from inhibition of the outward K+ current.

British Journal of Pharmacology (1998) 124, 1744–1750; doi:10.1038/sj.bjp.0702008
Differential effect of propofol on sympathetic neurotransmission in isolated human omental arteries and veins
Authors: Wallerstedt Susanna M , Bodelsson Mikael
Published: January 2005

The present study was undertaken to elucidate the effect of propofol on sympathetic neurotransmission in isolated human omental vessels.

Segments of both arteries and veins were exposed to 0, 10−7, 10−6, 10−5 or 10−4 M propofol, and studied in vitro to determine effects on: (i) isometric tension after electrical field stimulation (EFS) or after exogenous administration of noradrenaline (NA); (ii) EFS‐stimulated release of [3H]‐NA from vessel segments preincubated with [3H]‐NA; (iii) uptake of [3H]‐NA.

Propofol at 10−6 M enhanced EFS‐induced contraction in artery segments, 10−7 and 10−5 M had no effect, and 10−4 M propofol depressed EFS‐induced contraction in both artery and vein segments.

Propofol did not affect the response to exogenous NA in artery and vein segments.

EFS‐stimulated release of [3H]‐NA was depressed by 10−5 and 10−4 M propofol in artery segments, and by 10−4 M in vein segments.

Uptake of [3H]‐NA was depressed by 10−6–10−4 M propofol in artery but not in vein segments.

The results suggest that sympathetic neurotransmission is enhanced at clinical concentrations (10−6 M) of propofol in human omental arteries, but not veins. This may be due to an increased availability of NA in the neuromuscular junction resulting from a reduced presynaptic reuptake. Propofol at probably supraclinical concentrations (10−5–10−4 M) impairs the sympathetic neurotransmission in both human omental arteries and veins, probably due to an inhibitory effect on the NA release from the sympathetic nerves.

British Journal of Pharmacology (1998) 125, 120–126; doi:10.1038/sj.bjp.0702021
Assessment of the effect of malaria infection on hepatic clearance of dihydroartemisinin using rat liver perfusions and microsomes
Authors: Batty Kevin T , Ilett Kenneth F , Edwards Geoffrey , Powell Shane M , Maggs James L , Park B Kevin , Davis Timothy M E
Published: January 2005

The clearance of dihydroartemisinin (DHA) in control and malaria‐infected (MI) rats was investigated using the isolated perfused rat liver (IPRL) model and hepatic microsomal studies.

In the recirculating IPRL, clearance of DHA was reduced from a mean (s.d.) of 8.2±1.8 ml min−1 in controls (n=8) to 6.0±1.0 ml min−1 in MI (n=8; P<0.01). Clearance in control livers was similar to the perfusion flow rate, suggesting a high hepatic extraction ratio for DHA.

Single‐pass IPRL studies in controls (n=8) showed that DHA bioavailability at 1.3, 8 and 38 μM was 0.026±0.020, 0.043±0.025 and 0.14±0.06, respectively (P<0.001 for 8 μM vs 38 μM). In MI livers (n=5), DHA bioavailability at 8 and 38 μM was 0.18±0.07 and 0.40±0.08, respectively (P=0.002). Bioavailability was higher in the MI group than in controls (P=0.01 at 8 μM and P<0.001 at 38 μM). DHA‐glucuronide was the sole biliary metabolite.

Hepatic microsomal studies of DHA‐glucuronide formation showed a significantly lower Vmax, but no significant change in Km, in MI compared to control livers (n=6). Intrinsic metabolic clearance (Vmax/Km) was higher in control than in MI livers (5.2±1.3 and 2.5±1.4 μl min−1 mg−1, respectively; P=0.006).

These studies demonstrate that DHA has a high, concentration‐dependent hepatic extraction ratio that is reduced by 20–30% in the P. berghei rodent malaria model. The impaired hepatic clearance of DHA in MI is attributable to a reduction in intrinsic metabolic clearance.

British Journal of Pharmacology (1998) 125, 159–167; doi:10.1038/sj.bjp.0702023
Influence of various combinations of specific antibody dose and affinity on tissue imipramine redistribution
Authors: Ragusi Corinne , Boschi Gabrielle , Risède Patricia , Rips Richard , Harrison Kenneth , Scherrmann Jean‐Michel
Published: January 2005

This study was designed to evaluate the distribution kinetics of imipramine (Imip) in the brain and the main peripheral organs (heart, kidney, liver and lung) of rats, and to establish the relationship between the redistribution of Imip from these tissues and the immunoreactive capacity (dose and affinity) of anti‐TCA IgG.

[3H]‐Imip (1 nmol kg−1 body weight) was injected intravenously 6 min before the i.v. injection of antibodies. At this time, the concentrations of Imip and its main metabolites in plasma were determined. The radioactivity measured corresponded to 91.7% Imip, indicating that the pharmacokinetics reflected essentially Imip. Plasma and tissue Imip contents were measured over the interval 1 to 90 min in control and in treated rats. The antibodies used were a murine monoclonal IgG1 (Ka=3.8 107 M−1) at an IgG1/Imip molar ratio of 1000 (IgG1 1000), and a sheep polyclonal IgG (TAb, Ka=1.3 1010 M−1) at IgG/Imip molar ratios of 1, 10 and 100 (TAb1, TAb10 and TAb100).

The anti‐TCA IgG increased the plasma [3H]‐Imip concentrations: the AUC1→60 min for [3H]‐Imip were 4 (IgG1 1000), 9 (TAb1), 33.9 (TAb10) and 41.4 (TAb100) times higher in the treated groups than in the controls. The opposite effect occurred in the brain, heart and lungs, with large, rapid decreases in Imip. The increase in plasma Imip and the decrease in tissue Imip depended on the immunoreactive capacity (NKa) of the antibody, where N=molar concentration of IgG binding sites and Ka=IgG affinity constant. Maximal plasma and tissue redistribution occurred when NKa=33.8×104.

Imip redistribution can be controlled using various doses or affinities of specific antibodies, and the resulting rapid, extensive Imip redistribution from the main target organs could be very promising for TCA detoxification.

British Journal of Pharmacology (1998) 125, 35–40; doi:10.1038/sj.bjp.0702033
Potent vasodilatory with minor cardiodepressant actions of mibefradil in human cardiac tissue
Authors: Brixius Klara , Mohr Valeska , Müller‐Ehmsen Jochen , Hoischen Susanne , Münch Götz , Schwinger Robert H G
Published: January 2005

The present study compared the cardiovascular effects of mibefradil (MIB), a novel Ca2+‐channel antagonist with high selectivity for T‐type Ca2+‐channels to the effect of the L‐type Ca2+‐channel‐antagonists nifedipine (NIF) and diltiazem (DIL) in left ventricular myocardium and coronary arteries of hearts obtained from patients suffering from dilated cardiomyopathy (NYHA IV). Right atrial myocardium from patients undergoing aortocoronary bypass surgery without signs of cardiac failure was studied as well.

NIF and DIL (100 μmol l−1) completely depressed force of contraction (FOC) in electrically driven left ventricular myocardium (NIF 6.5±1.4% and DIL 7.1±1.2% of control), whereas a similar concentration of MIB only reduced force of contraction to 55.1±4.0% of the basal FOC. The negative inotropic potency as measured by the concentration needed to reduce basal FOC for 25% was NIF (0.0095 μmol l−1)>DIL (0.041 μmol l−1)>MIB (9.47 μmol l−1).

All three Ca2+‐channel antagonists were more potent in human atrial compared to human left ventricular myocardium to reduce FOC.

The rank order of Ca2+‐antagonistic moiety as measured by the decrease of the intracellular Ca2+‐transient (fura‐2 ratio method) was NIF>DIL>MIB.

All Ca2+‐channel antagonists completely relaxed human coronary arteries (% of papaverine effect: MIB 81.7±5.5%, DIL 91.3±0.9%, NIF 96.4±3.7%) precontracted with PGF2α (0.3 μmol l−1). The rank order of vasodilatory potency was NIF (EC50; 0.02 μmol l−1)>DIL (0.13 μmol l−1)>MIB (2.05 μmol l−1).

The vasoselectivity measured by the ratio of the concentration needed to achieve a 25% decrease in force and the concentration needed for 25% vasodilatation was 316 for MIB, 1.5 for NIF and 1.0 for DIL.

The present study provides evidence that blockade of T‐type Ca2+‐channels (e.g. mibefradil) results in potent vasodilatory properties with only minor cardiodepressant effects.

British Journal of Pharmacology (1998) 125, 41–48; doi:10.1038/sj.bjp.0702034
Pharmacological characterization of a rat 5‐hydroxytryptamine type3 receptor subunit (r5‐HT3A(b)) expressed in Xenopus laevis oocytes
Authors: Mair Ian D , Lambert Jeremy J , Yang Jay , Dempster John , Peters John A
Published: January 2005

The present study has utilized the two electrode voltage‐clamp technique to examine the pharmacological profile of a splice variant of the rat orthologue of the 5‐hydroxytryptamine type 3A subunit (5‐HT3A(b)) heterologously expressed in Xenopus laevis oocytes.

At negative holding potentials, bath applied 5‐HT (300 nM–10 μM) evoked a transient, concentration‐dependent (EC50=1.1±0.1 μM), inward current. The response reversed in sign at a holding potential of −2.1±1.6 mV.

The response to 5‐HT was mimicked by the 5‐HT3 receptor selective agonists 2‐methyl‐5‐HT (EC50=4.1±0.2 μM), 1‐phenylbiguanide (EC50=3.0±0.1 μM), 3‐chlorophenylbiguanide (EC50=140± 10 nM), 3,5‐dichlorophenylbiguanide (EC50=14.5±0.4 nM) and 2,5‐dichlorophenylbiguanide (EC50= 10.2±0.6 nM). With the exception of 2‐methyl‐5‐HT, all of the agonists tested elicited maximal current responses comparable to those produced by a saturating concentration (10 μM) of 5‐HT.

Responses evoked by 5‐HT at EC50 were blocked by the 5‐HT3 receptor selective antagonist ondansetron (IC50=231±22 pM) and by the less selective agents (+)‐tubocurarine (IC50=31.9± 0.01 nM) and cocaine (IC50=2.1±0.2 μM).

The data are discussed in the context of results previously obtained with the human and mouse orthologues of the 5‐HT3A subunit. Overall, the study reinforces the conclusion that species differences detected for native 5‐HT3 receptors extend to, and appear largely explained by, differences in the properties of homo‐oligomeric receptors formed from 5‐HT3A subunit orthologues.

British Journal of Pharmacology (1998) 124, 1667–1674; doi:10.1038/sj.bjp.0702037
Suppression of macrophage inflammatory protein (MIP)‐1α production and collagen‐induced arthritis by adenosine receptor agonists
Authors: Szabó Csaba , Scott Gwen S , Virág László , Egnaczyk Greg , Salzman Andrew L , Shanley Thomas P , Haskó György
Published: January 2005

Ligands of the various adenosine receptor subtypes modulate the production of pro‐and anti‐inflammatory cytokines. Here we evaluated the effect of adenosine and various ligands of the adenosine receptor subtypes (A1, A2, A3) on the chemokine macrophage inflammatory protein (MIP) 1α production in immunostimulated RAW macrophages in vitro. Furthermore, we studied whether a selected A3 adenosine receptor agonist inhibits MIP‐1α production and affects the course of inflammation in collagen‐induced arthritis.

In the cultured macrophages, the A3 receptor agonist N6‐(3‐iodobenzyl)‐adenosine‐5′‐N‐methyluronamide (IB‐MECA), and, less potently, the A2 receptor agonist 2‐p‐(2‐carboxyethyl) phenethylamino‐5′‐N‐ethyl‐carboxamidoadenosine (CGS; 1–200 μM) dose‐dependently suppressed the production of MIP‐1α. The selective A1 receptor agonist 2‐chloro‐N6‐cyclopentyladenosine (CCPA, 1–200 μM) was ineffective, and adenosine was a weak inhibitor. The inhibition of MIP‐1α production by the A3 and A2 agonist was associated with suppression of its steady‐state mRNA levels.

Based on the in vitro data, we concluded that activation of A3, and to a lesser extent A2 adenosine receptors suppresses MIP‐1α expression. Since IB‐MECA was the most potent inhibitor of MIP‐1α expression, we next investigated whether it affects the production of other pro‐inflammatory mediators. We observed that IB‐MECA (1–300 μM) inhibited, in a dose‐dependent manner, the production of IL‐12, IL‐6, and, to a lesser extent, nitric oxide in the immunostimulated cultured macrophages.

Since MIP‐α is a chemokine which enhances neutrophil recruitment into inflammatory sites, we investigated whether the A3 agonist IB‐MECA affects the course of inflammation, MIP‐α production and the degree of neutrophil recruitment in arthritis. In a model of collagen‐induced arthritis in mice, IB‐MECA (0.5 mg/kg/day) reduced the severity of joint inflammation. IB‐MECA inhibited the formation of MIP‐1α, IL‐12 and nitrotyrosine (an indicator of reactive nitrogen species) in the paws, and suppressed neutrophil infiltration.

We conclude that adenosine receptor agonists, most notably the A3 agonist IB‐MECA suppress the production of MIP‐α, and exert anti‐inflammatory effects. Therefore, stimulation of adenosine receptor subtypes A3 and A2 may be a strategy worthy of further evaluation for the abrogation of acute or chronic inflammatory disorders.

British Journal of Pharmacology (1998) 125, 379–387; doi:10.1038/sj.bjp.0702040
Evidence that S‐adenosyl‐L‐methionine diastereoisomers may reduce ischaemia‐reperfusion injury by interacting with purinoceptors in isolated rat liver
Authors: Dunne J Bruce , Alexander Barry , Williams Roger , Tredger J Michael
Published: January 2005

Mechanisms underlying the haemodynamic activity of diastereoisomers of S‐adenosyl‐L‐methionine (SAM) were investigated using inhibitors of purinoceptors and nitric oxide (NO) synthase in perfused rat livers damaged by sequential 24 h cold and 20 min rewarming ischaemia+reperfusion.

Stored livers were flushed with 10 ml saline alone (control) or with added (R,S) or (S,S) SAM (100 μM) and reperfused in the absence (control) or presence of 10 μM 8‐phenyltheophylline (8‐PT) or 100 μM L‐N‐monomethylarginine (L‐NMMA).

Both SAM diastereoisomers rapidly increased blood flow and bile production versus controls (P<0.001) but the (R,S) isomer induced greater increases in blood flow and the (S,S) isomer greater increases in bile production: 625 versus 596 versus 518 ml blood flow and 100 versus 119 versus 56 mg bile production per g liver over 3 h in (R,S), (S,S) and control, respectively.

8‐PT prevented the enhancement of blood flow by (S,S) SAM (529 versus 596 ml g −1liver over 3 h for (S,S) SAM alone, P<0.001), but was without effect in control livers. 8‐PT also reduced SAM‐enhanced bile production: 51 versus 119 mg g −1liver over 3 h, P<0.001. L‐NMMA reduced blood flow and bile production similarly in the absence or presence of (S,S) SAM.

Thus, SAM may improve liver perfusion after ischaemia‐reperfusion injury via stimulation of P1 (A2) purinoceptors at which SAM shows activity. The choleretic activity of (S,S) SAM is disproportionately greater than enhanced blood flow and may occur independently of a NO‐dependent component of bile production.

British Journal of Pharmacology (1998) 125, 225–233; doi:10.1038/sj.bjp.0702043
Human vascular to cardiac tissue selectivity of L‐ and T‐type calcium channel antagonists
Authors: Sarsero Doreen , Fujiwara Toshimasa , Molenaar Peter , Angus James A
Published: January 2005

Voltage‐operated calcium channel (VOCC) antagonists are effective antihypertensive and antianginal agents but they also depress myocardial contractility.

We compared four L‐type calcium channel antagonists, felodipine, nifedipine, amlodipine and verapamil and a relatively T‐type selective calcium channel antagonist, mibefradil, on human and rat isolated tissue assays to determine their functional vascular to cardiac tissue selectivity (V/C) ratio.

The V/C ratio was calculated as the ratio of the IC50 value of the antagonist that reduced (by 50%) submaximally contracted (K+ 62 mM) human small arteries from the aortic vasa vasorum (vascular, V) mounted in a myograph and the IC50 value of the antagonist that reduced (−)‐isoprenaline (6 nM) submaximally stimulated human right atrial trabeculae muscle (cardiac, C) mounted in organ chambers.

The average pIC50 values (−log IC50 M) for the human vascular preparations were felodipine 8.30, nifedipine 7.78, amlodipine 6.64, verapamil 6.26 and mibefradil 6.22. The average pIC50 values for the cardiac muscle were felodipine 7.21, nifedipine 6.95, verapamil 6.91, amlodipine 5.94, and mibefradil 4.61.

The V/C ratio calculated as antilog [pIC50V‐pIC50C] is thus mibefradil 41, felodipine 12, nifedipine 7, amlodipine 5 and verapamil 0.2.

In rat small mesenteric arteries the pIC50 values for the five drugs were similar to the values for human vasa vasorum arteries contracted by K+ 62 mM. However for methoxamine (10 μM) contraction in the rat arteries the pIC50 values were lower for felodipine 7.24 and nifedipine 6.23, but similar for verapamil 6.13, amlodipine 6.28 and mibefradil 5.91.

In conclusion, in the human tissue assays, the putative T‐channel antagonist mibefradil shows the highest vascular to cardiac selectivity ratio; some 3 fold higher than the dihydropyridine, felodipine, and some 200 fold more vascular selective than the phenylalkylamine, verapamil. This favourable vascular to cardiac selectivity for mibefradil, from a new chemical class of VOCC antagonist, may be explained by its putative T‐channel selectivity.

British Journal of Pharmacology (1998) 125, 109–119; doi:10.1038/sj.bjp.0702045
Fading and rebound of P2X2 currents at millimolar ATP concentrations caused by low pH
Authors: Stoop R , Quayle J M
Published: January 2005

When ATP is applied at high concentrations (above 1 mM) to PC12 cells, it produces a rapidly desensitizing peak current followed by a rebound of the current after termination of the ATP application. We expressed P2X2 receptors, which are thought to mediate the ATP currents of PC12 cells, in HEK293 cells and studied the effects of acidification on this ‘fading and rebound’ phenomenon. We found that the desensitization disappeared after adjusting the low pH (<5.0) of the millimolar ATP concentrations to a more physiological value (pH 7.3). Furthermore, the fading and rebound could also be induced at much lower ATP concentrations by decreasing the pH of the ATP containing application solutions. Thus, it appears this phenomenon is not caused directly by high concentrations of ATP, but is due to a concomitant acidification that occurs when high concentrations of ATP are dissolved in only moderately buffered application solutions.

British Journal of Pharmacology (1998) 125, 235–237; doi:10.1038/sj.bjp.0702056