bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of the peptide KPNFIRFamide (PF4) on the somatic muscle cells of the parasitic nematode Ascaris suum
Authors: Holden‐Dye L. , Brownlee D.J.A. , Walker R.J. 
Published: August 2006

Commonly used anthelmintic agents act on the muscle cells of parasitic nematodes to cause paralysis of the parasite and its expulsion from the host.
The motonervous system of nematodes contains neuropeptides, many of which are myoactive and elicit prolonged worm paralysis. Here we describe the actions of a novel peptide, KPNFIRFamide (Lys‐Pro‐Asn‐Phe‐Ileu‐Arg‐Phe‐amide; PF4), which mediates relaxation of the somatic muscle of the parasitic nematode Ascaris suum. Its mechanism of action is compared to that of the inhibitory neuromuscular junction transmitter, γ‐aminobutyric acid (GABA), which gates a chloride channel on Ascaris muscle.
Both PF4 and GABA hyperpolarized the muscle cells (EC50 values 98 nM and 59 μM, respectively; n = 6) and this was accompanied by an increase in input conductance.
The increase in input conductance elicited by PF4 and a supramaximal concentration of GABA were additive (10 μm PF4, 7.78 ± 1.88 μS; 10 mM GABA, 4.68 ± 1.39μS; 10 mM GABA and 10μm PF4 12.05±2.6 μS, n = 6, P<0.02 with respect to PF4 alone; P<0.01 with respect to GABA alone).
The membrane potential response to 10 μm PF4 initially consisted of a fast hyperpolarization that occurred within 1 min of PF4 application. The reversal potential for this early response to PF4 (PF4‐early) was determined at different extracellular chloride concentrations. Linear regression analysis of the natural logarithm of the extracellular chloride concentration against the reversal potential for PF4‐early yielded a straight line with a slope of −29.6±2.4 (‐34.4 to −24.9, 95% confidence limits; r2 = 0.82). This is close to the slope of −26.5 for a chloride‐dependent event, as predicted by the Nernst equation. There was a significant correlation between the reversal potential for this event and the reversal potential for GABA (r = 0.94; P<0.001; n = 12).
The late response to PF4 (PF4‐late) appeared after 1 min and consisted of a slow reduction in the hyperpolarization to a plateau level, before the return of the membrane potential to the resting value. PF4‐late is not likely to be a chloride‐dependent event as during the hyperpolarization caused by a supramaximal concentration of GABA the muscle cells depolarized when a supramaximal concentration of PF4 was added to the perfusate. The membrane potential in the presence of 1 mM GABA was −61.8±4.8 mV and in the presence of 1 mM GABA with 10 μm PF4 was −47.5± 1.5 mV (P<0.02; n = 6).
The conductance increase elicited by 30 μm GABA was blocked by 10 μm ivermectin (before ivermectin 0.97 ±0.2 μS, after ivermectin 0.33 ±0.12 μS; n = 5; P<0.05; Student's paired t test) but the conductance increase elicited by 1 μm PF4 was not (before ivermectin 0.96±0.14 μS, after ivermectin 1.07±0.19 μS; n = 0.34; Student's paired t test).
These data indicate that PF4 elicits a potent, inhibition of Ascaris muscle cells which is partially mediated by chloride and which is independent of the inhibitory GABA receptor.
Functional GABAAreceptors on rat vagal afferent neurones
Authors: Ashworth‐Preece Mark , Krstew Elena , Jarrott Bevyn , Lawrence Andrew J. 
Published: August 2006

In the present study,in vitroelectrophysiology and receptor autoradiography were used to determine whether rat vagal afferent neurones possess γ‐aminobutyric acid (GABA)Areceptors.GABA (1‐100 μM) and isoguvacine (3–100 μm) caused a concentration‐dependent depolarization of the rat isolated nodose ganglion preparation at room temperature. When applied to the tissue 20 min before the agonist, SR95531 (3 μm) and bicuculline (3μm) caused a parallel shift to the right of the GABA and isoguvacine concentration‐response curves, yielding shifts of 81 fold and 117 fold for SR95531 and 4 fold and 12 fold for bicuculline, respectively.Baclofen (10 nM‐100 μm) was unable to elicit a depolarization of the rat isolated nodose ganglion preparation at either room temperature or at 36°C, whilst 5‐aminovaleric acid (10 μm), a GABABreceptor antagonist, was unable to antagonize significantly the GABA‐induced depolarization at either room temperature or at 36°C.[3H]‐SR95531 (7.2 nM), a GABAAreceptor‐selective antagonist, bound topographically to sections of rat brainstem. Specific binding was highest in the medial nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus nerve (DMVN). Binding was also observed in certain medullary reticular nuclei, in particular the parvocellular reticular nucleus.Unilateral nodose ganglionectomy caused a reduction in GABAAbinding site density in the medial NTS from 93 ± 7 to 68 ± 6 d.p.m./mm2. This procedure also caused a reduction in GABAAbinding site density in the side of the NTS contralateral to the lesion, from 151 ± 12 to 93 ± 7 d.p.m./mm2. Sham surgery had no effect on the binding of [3H]‐SR95531 in rat brainstem.The present data provide evidence for the presence of GABAAreceptors located on the soma and central terminals of rat vagal afferent neurones. Additionally, a population of GABAAreceptors is evidenced postsynaptically in the rat NTS with respect to vagal afferent terminals. These data are discussed in relation to the functional pharmacology of GABA in this region of the NTS.
Preliminary characterization of the role of protein serine/ threonine phosphatases in the regulation of human lung mast cell function
Authors: Peirce Matthew J , Cox Sarah E , Munday Michael R , Peachell Peter T 
Published: August 2006

Okadaic acid, a cell permeant inhibitor of protein serine/threonine phosphatases (PPs), attenuated the IgE‐dependent release of mediators from human lung mast cells (HLMC). The concentration of okadaic acid required to inhibit by 50% (IC50) the IgE‐dependent release of histamine was 0.2 μm. Okadaic acid also inhibited the IgE‐mediated generation of prostaglandin D2(PGD2) and sulphopeptidoleukotrienes (sLT) with IC50values of 0.2 μmand 0.6 μmrespectively.The IgE‐mediated generation of histamine, PGD2and sLT was inhibited by okadaic acid and two analogues of okadaic acid, okadaol and okadaone, with the following rank order of activity; okadaic acid>okadaol>okadaone. This order of activity for the inhibition of mediator release parallels the activity of these compounds as inhibitors of isolated PPs.Extracts of HLMC liberated32P from radiolabelled glycogen phosphorylase and this PP activity was inhibited by the PP inhibitors (all at 3 μm), okadaic acid (73±4% inhibition,P<0.0005), okadaol (26±7% inhibition,P<0.05) and okadaone (8±7% inhibition,P=0.52). The rank order of activity of okadaic acid>okadaol>okadaone parallels the activity of these compounds as inhibitors of isolated PPs.Dephosphorylation of radiolabelled glycogen phosphorylase by extracts of HLMC was inhibited by 15±3% (P<0.001) by a low (2 nm) concentration of okadaic acid and by 88±4% (P<0.0005) by a higher (5 μm) concentration of okadaic acid. Because 2 nmokadaic acid may act selectively to inhibit PP2A whereas 5 μmokadaic acid inhibits both PP1 and PP2A, these data suggest that both PP1 and PP2A are present in HLMC.Inhibitor 2, a PP1‐selective inhibitor, attenuated (71±3% inhibition,P<0.05) PP activity in extracts of HLMC suggesting that HLMC contain PP1 and that it may constitute 71% of the phosphorylase PP activity in extracts of HLMC.Radiolabelled casein, a PP2A‐restricted substrate, was dephosphorylated by extracts of purified HLMC and this activity was inhibited (81±8% inhibition,P<0.005) by 2 nmokadaic acid suggesting that PP2A is resident in HLMC.Collectively, these data suggest that both PP1 and PP2A are resident in HLMC. However, although the data suggest that okadaic acid regulates responses in HLMC by interacting with PPs, it has not been possible to determine whether either PP1 or PP2A or both PPs are involved in the okadaic acid‐induced inhibition of mediator release from HLMC.British Journal of Pharmacology(1997)120, 239–246; doi:10.1038/sj.bjp.0700915
Evidence that both nitric oxide (NO) and a non‐NO hyperpolarizing factor elicit NANC nerve‐mediated relaxation in the rat isolated anococcygeus
Authors: Selemidis S. , Cocks T.M. 
Published: August 2006

Responses to electrical field stimulation (EFS; 0.5–10 Hz, 0.2 ms duration, supramaximal voltage for 20 s) of non‐adrenergic, non‐cholinergic, (NANC) nerves were obtained in preparations of rat anococcygeus pre‐contracted with titrated concentrations of phenylephrine (0.1–1 μM) to ∼40% of their maximum contraction to phenylephrine (Fmax) regardless of drug treatment.
With this set level of active force, NANC nerve stimulation resulted in relaxations that were maximal (peak relaxation) at 0.5–1 Hz, abolished by tetrodotoxin (1 μM) but only minimally blocked by the nitric oxide synthase (NOS) inhibitor, NG‐nitro‐L‐arginine, (L‐NOARG; 100 μM). Furthermore, the nitric oxide (NO) scavenger, oxyhaemoglobin (HbO; 30 μM) gave no further block alone or in combination with L‐NOARG (100 μM). By comparison, in preparations contracted with phenylephrine to ∼70% Fmax, relaxations to NANC nerve stimulation were markedly reduced or abolished by combined treatment with L‐NOARG (100 μM) and HbO (30 μM).
Nifedipine (0.3 μM) significantly inhibited NANC nerve‐mediated relaxations, which became frequency‐dependent and abolished those resistant to L‐NOARG (100 μM) and HbO (30 μM).
These data suggest that a non‐NO, hyperpolarizing factor and NO both contribute to NANC nerve‐mediated inhibitory responses in the rat anococcygeus. However, responses to the non‐NO factor were observed only in preparations contracted sub‐maximally by a nifedipine‐sensitive mechanism.
Characterization of the P2 receptors in rabbit pulmonary artery
Authors: Qasabian R.A. , Schyvens C. , Owe‐Young R. , Killen J.P. , Macdonald P.S. , Conigrave A.D. , Williamson D. 
Published: August 2006

We have identified the P2 receptors mediating vasomotor responses in the rabbit pulmonary artery.
Neither ATP nor UTP contracted intact or endothelium‐denuded rings. However, both relaxed intact rings of rabbit pulmonary artery that had been preconstricted with phenylephrine (pD2 5.2 and 5.6, respectively).
The vasodilator effect of UTP was endothelium‐dependent and abolished by the nitric oxide synthase inhibitor NG‐nitro‐L‐arginine (L‐NOARG).
The vasodilator effect of ATP was only partially inhibited by removal of endothelium or addition of L‐NOARG, suggesting an additional direct effect on vascular smooth muscle.
The endothelium‐dependent vasodilator responses to UTP and ATP were competitively antagonized by suramin.
Preconstricted, endothelium‐denuded rings were also relaxed by 2‐methylthio ATP (pD2 6.6), a P2Y receptor agonist.
Ca2+‐mobilizing P2U receptors were identified on smooth muscle cells on the basis of single cell responses to ATP (pD2 7.8) and UTP (pD2 7.9; 6.7 in the presence of 100 μm suramin).
There was no evidence of a Ca2+‐mobilizing P2Y receptor in these cultured cells.
The data suggest the presence of (i) a suramin‐sensitive P2U receptor on endothelial cells that induces vasorelaxation through NO release, (ii) a suramin‐sensitive P2U receptor on cultured smooth muscle cells that mobilizes Ca2+ but is not coupled to vasomotor responses and (iii) a putative P2Y receptor on vascular smooth muscle cells that induces relaxation via a Ca2+‐independent signal transduction pathway.
Inhibitory effects of TAK‐044 on endothelin induced vasoconstriction in various canine arteries and porcine coronary arteries: a comparison with selective ETA and ETB receptor antagonists
Authors: Awane‐Igata Yumiko , Ikeda Shota , Watanabe Toshifumi 
Published: August 2006

The inhibitory effects of the endothelin (ET) receptor antagonist, TAK‐044, on ET‐induced vasoconstriction in various canine arteries and porcine coronary arteries were studied and were compared to those of selective ETA and ETB receptor antagonists.
ET‐1 (0.1 nM‐0.3 μm) caused vasoconstriction in canine coronary, femoral, renal, mesenteric and basilar arteries, and the strongest responses were obtained in coronary and basilar arteries. TAK‐044 (10 nM, 100 nM) inhibited this ET‐1‐induced vasoconstriction except in the case of mesenteric arteries. The strongest inhibitory effects were obtained in coronary arteries; an EC50 value for ET‐1 was 5.2 ± 0.77 nM (n = 12) in the control and 24 ± 3.8 nM (n = 4) in the presence of TAK‐044 at 10 nM. BQ‐123 (1 μm) inhibited the vasoconstriction in coronary and femoral arteries but did not in renal, mesenteric or basilar arteries.
TAK‐044 (10–100 nM) inhibited the ET‐1‐induced vasoconstriction in porcine coronary arteries to a degree similar to that in canine coronary arteries. In contrast, BQ‐123 (10 μm) did not inhibit the contraction completely, and a BQ‐123‐insensitive component was identified. Although BQ‐788 (1 μm) did not modify the concentration‐response curve at all, it abolished the BQ‐123‐insensitive component when applied together with BQ‐123 (10 μM).
Sarafotoxin S6c (10 pM‐30 nM) caused vasoconstriction in porcine coronary arteries with the maximum amplitude of the contraction being 39% of that with ET‐1. Both TAK‐044 (10 nM, 100 nM) and BQ‐788 (1 μM) inhibited this vasoconstriction, while BQ‐123 (3 μM, 10 μm) did not.
Vasoconstriction induced by ET‐3 (0.1 nM‐0.3 μm) in porcine coronary arteries showed a concentration‐response curve with two distinct phases in contrast to that seen with sarafotoxin S6c. TAK‐044 (0.3 nM‐10 nM) inhibited both phases in a concentration‐dependent manner. BQ‐123 (1 μM, 3 μm) inhibited only the second phase, while BQ‐788 (1 μm) inhibited the first phase.
We concluded that the inhibitory effects of TAK‐044 on ET‐1‐induced vasoconstriction were the strongest in coronary arteries among the canine arteries examined. In addition, we showed that both ETA and ETB receptors mediate vasoconstriction in porcine coronary arteries and TAK‐044 inhibits the vasoconstriction mediated by both of these receptors.
The effect of the protein phosphatases inhibitor cantharidin on β‐adrenoceptor‐mediated vasorelaxation
Authors: Knapp Jörg , Bokník Peter , Linck Bettina , Luss Hartmut , Müller Frank U. , Neumann Peter Nacke Joachim , Vahlensieck Ute , Schmitz Wilhelm 
Published: August 2006

Cantharidin, an inhibitor of protein phosphatase types 1 (PP1) and 2A (PP2A), increased basal tone of bovine isolated coronary artery rings (CARs) with and without endothelium in a time‐and concentration‐dependent manner with pEC50 values of about 5.1 and 5.2, respectively, for both preparations.
β‐Adrenoceptor stimulation with isoprenaline (Iso; 0.03–100 μm) or inhibition of phosphodiesterase activity by 3‐isobutyl‐l‐methylxanthine (IBMX; 10–1000 μm), respectively, relaxed CARs precontracted with KC1 (75 mm). CARs with and without endothelium showed no difference in the relaxing response to Iso and IBMX, respectively.
Cantharidin (3 μm) attenuated vasorelaxation induced by Iso (0.03–100 μm) in CARs with and without endothelium in a time‐dependent manner, whereas vasorelaxation induced by IBMX (10–1000 μm) was not attenuated by 3 μM cantharidin.
Cantharidin (3 μm) did not affect cyclic AMP content in bovine cultured vascular cells, i.e. coronary artery smooth muscle cells (BCs), aortic endothelial cells (BAECs) and aortic smooth muscle cells (BASMCs), either under basal conditions, after β‐adrenoceptor stimulation (Iso) or inhibition of phosphodiesterase activity (IBMX), respectively.
Cantharidin inhibited protein phosphatase activity in homogenates from bovine coronary artery rings with a pIC50 of about 6.0. In homogenates of bovine cultured vascular cells pIC50 values of cantharidin amounted to about 6.5 for BCs, 6.7 for BAECs and 6.7 for BASMCs, respectively.
It was concluded that cantharidin differently affects vasorelaxation due to stimulation of [3‐adrenoceptors (Iso) or inhibition of phosphodiesterase activity (IBMX), respectively. The attenuation of β‐adrenoceptor‐mediated vasorelaxation by phosphatase inhibition is not due to diminished adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) generation but could be evidence for different subcellular compartments of cyclic AMP.
Activation and inhibition of rat neuronal nicotinic receptors by ABT‐418
Authors: Papke Roger L. , Thinschmidt Jeffrey S. , Moulton Becky A. , Meyer Edwin M. , Poirier Amy 
Published: August 2006

ABT‐418 appeared to function as a relatively broad spectrum activator of neuronal nicotinic receptors, expressed in Xenopus oocytes, with little cross reactivity to the mammalian muscle receptor subtype. However, the relative potencies of ABT‐418 at the various subtypes differed from those acetylcholine (ACh). For example, ACh was most potent at α3β2 (EC50 ∼30 μM) and least potent at α2β2 (EC50∼500 μM). ABT‐418 was most potent at α4β2 and α2β2 (EC50∼6 μM and 11 μM, respectively) and least potent at α3β4 (EC50 ∼188 μM).
In addition to activating neuronal receptors, ABT‐418 exhibited complex properties, including the inhibition of ACh responses.
The current responses elicited by relatively high concentrations of ABT‐418 on the α4β2 receptor subtype were protracted beyond the application interval. The coapplication of ABT‐418 with either of the use‐dependent inhibitors bis(1,2,2,6,6‐tetramethyl‐4‐pipendimyl)sebacate (BTMPS) or tetramethyl‐pipenidine (TMP) eliminated the late protracted phase of the currents with only small effects on the initial activation phase. When the reversible inhibitor TMP was washed from the bath, the previously inhibited late current reappeared, suggesting that the observed mixed agonist‐antagonist effects of ABT‐418 and (±)‐epibatidine on α4β2 were due to a concentration‐dependent noncompetitive inhibition, an effect similar to that obtained for (−)‐nicotine.
The inhibition of α4β2 receptors by ABT‐418 was voltage‐dependent. When high concentrations of ABT‐418 were applied under depolarizing conditions, additional late currents could be observed under conditions which suggested that a build up of ABT‐418 in an unstirred layer over the surface of the oocyte was occurring. This may have been due to the dissociation of the drug from channel blocking sites on the receptors themselves, or alternatively, from the plasma membrane of the cells.
Evidence against a role of cytochrome P450‐derived arachidonic acid metabolites in endothelium‐dependent hyperpolarization by acetylcholine in rat isolated mesenteric artery
Authors: Fukao Mitsuhiro , Hattori Yuichi , Kanno Morio , Sakuma Ichiro , Kitabatake Akira 
Published: August 2006

In rat mesenteric artery, acetylcholine (ACh) causes endothelium‐dependent hyperpolarization by releasing endothelium‐derived hyerpolarizing factor (EDHF). Recent evidence suggests that EDHF may be a cytochrome P450‐derived arachidonic acid metabolite. The aim of the present study was to investigate whether such a metabolite is indeed contributing to ACh‐induced hyperpolarization observed in rat mesenteric artery.
The phospholipase A2 inhibitor quinacrine (30 μm) nearly completely eliminated ACh‐induced hyperpolarization. However, the hyperpolarizing effect of pinacidil was also abolished in the presence of quinacrine.
The imidazole antimycotic agents ketoconazole (50 μm), clotrimazole (30 μm) and miconazole (10 μm), which bind to the heme moiety of cytochrome P450, eliminated not only ACh‐induced hyperpolarizations but also those induced by pinacidil. SKF525A (30 μm), a prototype inhibitor of the enzyme, also abolished the hyperpolarizing responses to both agents. In contrast, neither 17‐octadecynoic acid (10 μm), a mechanism‐based inhibitor of cytochrome P450 metabolism of fatty acids, nor eicosatetraynoic acid (20 μm), an inhibitor of all arachidonic acid metabolic pathways, altered ACh‐induced hyperpolarization. Furthermore, the hyperpolarization was unaffected by the preferential inhibitors of specific cytochrome P450 isozymes, α‐naphtofiavone (1 μm), diedthyldithiocarbamate (50 μm), metyrapone (20 μm) and troleandomycin (10 μm).
Pretreatment of rats with lipopolysaccharide (2mgkg−1) and exposure to nitroprusside (10 μm), both of which are expected to inhibit cytochrome P450 activity due to nitric oxide overproduction, were without effect on ACh‐induced hyperpolarization. Pretreatment of rats for 3 days with pentobarbitone (80 mg kg−1 day−1), a cytochrome P450 inducer, also did not affect the hyperpolarizing response to ACh.
Arachidonic acid in concentrations up to 100 μM had no detectable effect on smooth muscle membrane potential. 11,12‐Epoxyeicosatrienoic acid (EET, 10 μm), one of cytochrome P450‐derived epoxygenase metabolites of arachidonic acid, elicited a small endothelium‐independent membrane hyperpolarization. The hyperpolarizing response to EET was blocked by glibenclamide (30 μm), in contrast to the response to ACh.
These results suggest that the contribution of a cytochrome P450‐derived metabolite of arachidonic acid to ACh‐induced hyperpolarization via EDHF release is minimal or absent in rat mesenteric artery.
Responses of rat substantia nigra dopamine‐containing neurones to (−)‐HA‐966 in vitro
Authors: Grobaski Kenneth C. , Ping Hanxian , Da Silva Helena M.A. , Bowery Norman G. , Connelly Stephen T. , Shepard Paul D. 
Published: August 2006

Extracellular single unit recording techniques were used to compare the effects of (−)‐3‐amino‐l‐hydroxypyrrolidin‐2‐one ((—)‐HA‐966) and (±)‐baclofen on the activity of dopamine‐containing neurones in 300 μm slices of rat substantia nigra. Electrophysiological data were compared with the outcome of in vitro binding experiments designed to assess the affinity of (—)‐HA‐966 for γ‐aminobutyric acid (GABAB) receptors.
Bath application of (—)‐HA‐966 produced a concentration‐dependent inhibition of dopaminergic neuronal firing (EC50 = 444.0 μM; 95% confidence interval: 277.6 μm‐710.1 μM, n = 27) which was fully reversible upon washout from the recording chamber. Although similar effects were observed in response to (±)‐baclofen, the direct‐acting GABAB receptor agonist proved to be considerably more potent than (−)‐HA‐966 (EC50 = 0.54 μM; 95% confidence interval: 0.44 μm‐0.66 μM, n = 29) in vitro.
Low concentrations of chloral hydrate (10 μM) were without effect on the basal firing rate of nigral dopaminergic neurones but significantly increased the inhibitory effects produced by concomitant application of (—)‐HA‐966.
The inhibitory effects of (—)‐HA‐966 were completely reversed in the presence of the GABAB receptor antagonists, CGP‐35348 (100 μM) and 2‐hydroxysaclofen (500 μM). Bath application of CGP‐35348 alone increased basal firing rate. However, the magnitude of the excitation (9.2 ± 0.3%) was not sufficient to account for the ability of the antagonist to reverse fully the inhibitory effects of (—)‐HA‐966.
(—)‐HA‐966 (0.1–1.0 mM) produced a concentration‐dependent displacement of [3H]‐GABA from synaptic membranes in the presence of isoguvacine (40 μM). However, the affinity of the drug for GABAB binding sites was significantly less than that of GABA (0.0005 potency ratio) and showed no apparent stereoselectivity.
These results indicate that while (—)‐HA‐966 appears to act as a direct GABAB receptor agonist in vitro, its affinity for this receptor site is substantially less than that of GABA or baclofen and unlikely to account for the depressant actions of this drug which occur at levels approximately ten fold lower in vivo.