bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of kinin receptors modulating neurogenic contractions of the mouse isolated vas deferens
Authors: Maas Jonny , Rae Giles A. , Huidobro‐Toro Juan P. , Calixto João B. 
Published: July 2012

1 This study analyses the receptors mediating the effects of bradykinin (BK) and analogues on neurogenic twitch contractions of the mouse isolated vas deferens evoked, in the presence of captopril (3 μm), by electrical field stimulation with trains of 4 rectangular 0.5 ms pulses of supramaximal strength, delivered at a frequency of 10 Hz every 20 s.2 BK (0.1–300 nM) induced a graded potentiation of twitches, with an EC50 (geometric mean and 95% confidence limits) of 4.5 nM (1.7–11.6) and an Emax of 315 ± 19 mg per 10 mg of wet tissue (n = 6). Similar results were obtained in tissues challenged with Lys‐BK, [Hyp3]‐BK, Met, Lys‐BK and the selective B2 receptor agonist [Tyr(Me)8]‐BK (0.1–300 nM).3 The selective B2 receptor antagonists, Hoe 140 (1–10 nM) and NPC 17731 (3–30 nM), caused graded rightward shifts of the curve to BK‐induced twitch potentiation, yielding apparent pA2 values of 9.65 ± 0.09 and 9.08 ±0.13, respectively, and Schild plot slopes not different from 1. Both antagonists (100 nM) failed to modify similar twitch potentiations induced by substance P (3 nM) or endothelin‐1 (1 nM). Preincubation with the selective B1 receptor antagonist, [Leu8des‐Arg9‐BK (1 μm), increased the potentiating effect of BK on twitches at 30–300 nM.4 In contrast to BK, the selective B1 receptor agonist, [des‐Arg9‐BK (0.3–1000 nM) reduced the amplitude of twitches in a graded fashion, with an IC50 of 13.7 nM (10.4–16.1) and an Imax of 175 ± 11 mg (n = 4). The twitch depression induced by [des‐Arg9]‐BK (300 nM) was not affected by Hoe 140 (30 nM) or NPC 17731 (100 nM), but was abolished by the selective B1 receptor antagonist, [Leu8des‐Arg9‐BK (1 μm), which did not modify the twitch inhibitory effect of clonidine (1 nM) or morphine (300 nM).5 In non‐stimulated preparations, BK (100 nM) also potentiated, in a Hoe 140‐sensitive (10 nM) manner, the contractions induced by ATP (100 μm), but not by noradrenaline (10 μm), whereas [des‐Arg9]‐BK (300 nM) did not modify the contractions induced by either agonist.6 It is concluded that the mouse vas deferens expresses both B1 and B2 receptors, which modulate sympathetic neurotransmission in opposing ways. Neurogenic contractions are inhibited by stimulation of possibly prejunctional B1 receptors, whereas activation of B2 receptors increases twitch contractions, in part by amplifying the responsiveness of the smooth muscle cells to the sympathetic co‐transmitter ATP.
G‐protein involvement in muscarinic receptor‐stimulation of inositol phosphates in longitudinal smooth muscle from the small intestine of the guinea‐pig
Authors: Prestwich S.A. , Bolton T.B. 
Published: July 2012

Aluminium fluoride (AlF), pertussis toxin (PTX) and cholera toxin (ChTX) have been used to examine the involvement of G‐proteins during muscarinic acetylcholine receptor (AChR) stimulation of inositol phospholipid hydrolysis in fragments of longitudinal smooth muscle from the small intestine of the guinea‐pig.
Carbachol (CCh) induced time‐ and concentration‐dependent increases in [3H]‐inositol monophosphates, [3H]‐inositol (1,4) bisphosphate, [3H]‐inositol (1,3,4) trisphosphate, [3H]‐inositol (1,4,5) trisphosphate ([3H]‐Ins (1,4,5)P3) and [3H]‐inositol tetrakisphosphates measured by h.p.l.c. These increases were inhibited >95% in the presence of the muscarinic AChR antagonist atropine (0.5 μm).
AlF transiently increased the basal levels of [3H]‐Ins (1,4,5)P3 but increases in the levels of the other [3H]‐inositol phosphates occurred more slowly. CCh‐induced increases in the levels of all the [3H]‐inositol phosphates were strongly inhibited in the presence of AlF.
PTX had no effect on basal levels of any of the [3H]‐inositol phosphates but reduced the effects of CCh on these; ChTX had no effects on either basal or CCh‐stimulated levels.
It was concluded that muscarinic AChR‐stimulated increases in the levels of [3H]‐inositol phosphates occur via both a PTX‐sensitive G‐protein and a PTX‐insensitive mechanism. The actions of AlF may suggest the involvement of an inhibitory G‐protein in the regulation of muscarinic AChR‐stimulated inositol phospholipid turnover.
Increase in tone and intracellular Ca2+ in rabbit isolated ear artery by platelet‐derived growth factor
Authors: Hughes A.D. 
Published: July 2012

The effect of platelet‐derived growth factor (PDGF‐AB) on tone and intracellular Ca2+ ([Ca2+]i) was examined in rabbit isolated ear arteries. Arteries were mounted in a myograph and loaded with the Ca2+‐sensitive fluorescent indicator, fura‐2, for concurrent measurements of isometric force and [Ca2+]i.
PDGF‐AB contracted rabbit ear artery in a concentration‐dependent manner. PDGF‐AB induced tone was associated with a rise in [Ca2+]i. In the presence of noradrenaline, PDGF‐AB induced a similar rise in [Ca2+]i but contraction in response to PDGF‐AB in the presence of noradrenaline was increased compared with PDGF‐AB alone.
PDGF‐AB‐induced rise in [Ca2+]i and tone were abolished by removal of extracellular Ca2+ (with addition of BAPTA, a Ca2+ chelator), and by preincubation with a dihydropyridine calcium channel blocker, (−)−202 791. Bistyrphostin, a selective inhibitor of tyrosine kinases, also inhibited PDGF‐AB‐induced tone, but had no effect on noradrenaline‐ or potassium‐induced tone.
PDGF‐AB contracts rabbit ear artery by increasing Ca2+ entry through voltage‐operated calcium channels. This effect involves activation of a tyrosine kinase.
Vascular pharmacology of methylene blue in vitro and in vivo: a comparison with NG‐nitro‐l‐arginine and diphenyleneiodonium
Authors: Wang Yong‐Xiang , Cheng Xing , Pang Catherine C.Y. 
Published: July 2012

The vascular effects of the soluble guanylyl cyclase inhibitor, methylene blue as well as the nitric oxide (NO) synthase inhibitors, NG‐nitro‐l‐arginine (l‐NOARG) and diphenyleneiodonium (DPI) were studied in rat isolated aortic rings and conscious, unrestrained rats.
Acetylcholine (ACh) and sodium nitroprusside (SNP) caused concentration‐dependent relaxation of preconstricted aortic rings. Both methylene blue (1 × 10−5m) and l‐NOARG (3 × 10−5m) abolished ACh‐induced relaxation; however, methylene blue but not l‐NOARG shifted the concentration‐response curve of SNP to the right.
In conscious rats, i.v. infusion of methylene blue (1.1 × 10−5mol kg−1 min−1), at a concentration which reduced the aortic tissue level of cyclic GMP by 50%, did not significantly alter mean arterial pressure (MAP) and heart rate (HR). In contrast, i.v. bolus injection of l‐NOARG (1.5 × 10−4 mol kg−1) markedly increased MAP and decreased HR.
Both ACh and SNP dose‐dependently decreased MAP in conscious rats. Methylene blue did not alter the magnitude or duration of ACh‐ or SNP‐induced depressor responses. l‐NOARG, on the other hand, significantly though incompletely, reduced the magnitude and duration of the depressor response to ACh but not SNP. The depressor response to ACh or SNP was not altered by pretreatment with indomethacin (1.4 × 10−5 mol kg−1) or capsaicin (3.3 × 10−4 mol kg−1).
NG‐nitro‐l‐arginine methyl ester (l‐NAME) also caused dose‐dependent increases in MAP in conscious rats. Both methylene blue and DPI (1 × 10−5 mol kg−1) selectively shifted the dose‐pressor response curve of l‐NAME to the right.
These results suggest that: (1) the inhibition of endogenous NO biosynthesis does not necessarily lead to pressor response in vivo, (2) l‐NOARG may not produce pressor response solely via the inhibition of endogenous endothelial NO biosynthesis, and (3) the depressor responses to ACh and SNP may not involve the release of NO or prostanoids or afferent nerve transmitters.
Inotropic changes induced by fluoroaluminates in rabbit left atrial muscles: possible involvement of G proteins
Authors: Hattori Yuichi , Imamura Michialki , Akaishi Yasuhiro , Kanno Morio 
Published: July 2012

The effects of fluoroaluminate complexes (NaF plus AlCl3) on force of contraction, cyclic AMP accumulation and phosphoinositide hydrolysis were examined in rabbit left atrial muscles.
Fluoroaluminates (1–10 mm NaF + 10 μm AlCl3) produced a biphasic inotropic response which was composed of an early small decline and subsequent increase in force of contraction. In the presence of the Al3+ chelator, deferoxamine (100 μm), the positive inotropic response was completely abolished and a sustained negative inotropic response appeared, suggesting that only the positive inotropic response is due to the action of fluoroaluminates.
The positive inotropic effect of fluoroaluminates was associated with a significant increase in the total duration of a single contraction; the time to peak tension and relaxation time were prolonged. In contrast, these parameters were substantially abbreviated by isoprenaline or histamine.
When force of contraction was increased by isoprenaline or histamine, the addition of fluoroaluminates caused a marked negative inotropic effect, which was eliminated by pretreatment with pertussis toxin.
Fluoroaluminates did not cause a significant increase in cyclic AMP content at concentrations of NaF in the range of 1–10 mm. However, the content of cyclic AMP was greatly elevated by fluoroaluminates when the atrial muscles were pretreated with pertussis toxin.
Accumulation of [3H]‐inositol monophosphate in atrial muscle strips prelabelled with myo‐[3H]‐inositol was significantly increased by fluoroaluminates at concentrations of NaF over 1 mm. The phosphoinositide response to fluoroaluminates remained unchanged with pertussis toxin pretreatment.
These results indicate that, in rabbit left atrial muscles, fluoroaluminates produce a positive inotropic effect which may be mediated by Gq but not by Gs proteins; they produce a negative inotropic effect possibly through Gi only when Gs is activated with other agents.
The biphasic response of rat vesical smooth muscle to ATP
Authors: Bolego Chiara , Pinna Christian , Abbracchoi Maria P. , Cattabeni Flaminio , Puglisi Lina 
Published: July 2012

Adenosine‐5′‐triphosphate (ATP) is known to exert a variety of biological effects via the activation of either ionotropic P2X‐ or G‐protein coupled P2Y‐purinoceptor subtypes. In this study the effects induced by ATP and ATP analogues on rat bladder strips were characterized at resting tone and in carbachol‐prestimulated tissues.
ATP exerted a clear concentration‐dependent biphasic response, which was maximal at 1 mM concentration and was characterized by an immediate and transient contraction, followed by a slower sustained relaxation. The receptor mediating contraction was susceptible to desensitization by ATP and by the ATP analogue, α,β‐methyleneATP (α,β‐meATP) showing the typical features of the P2X‐purinoceptor; conversely, ATP‐evoked relaxation did not undergo tachyphylaxis following either ATP or α,β‐meATP.
The slower and sustained relaxant phase seemed to be due to activation of P2Y‐purinoceptors, based on responses obtained with the P2Y agonist, 2‐methyl‐thioATP (2‐meSATP) and, more importantly, based on the clear involvement of the G‐proteins. In fact, the G‐protein activator, guanosine 5′‐O‐(3‐thiotriphosphate) (GTPγS) significantly potentiated and the G‐protein blocking agent, guanosine 5′‐O‐(2‐thio‐diphosphate) (GDPβS) completely abolished the ATP‐induced relaxation. No effects were exerted by these two G‐protein modulators on the ATP‐induced contraction.
The relaxant component of the ATP response of bladder tissue was not significantly influenced by nitro‐benzyl‐thioinosine (NBTI) or by 8‐phenyltheophylline (8‐PT), suggesting that the contribution of the ATP metabolite adenosine to this response was negligible. Moreover, relaxation evoked by ATP and by the adenosine analogue, 5′‐N‐ethylcarboxamidoadenosine (NECA) was additive.
Suramin was unable to modify either the relaxant or the contractile responses of bladder strips to ATP. However, when tested on the concentration‐response curve to the slowly hydrolysable P2x‐agonist α,β‐meATP, a rightward shift was detected, suggesting that ATP contractile responses are mediated by suramine‐sensitive P2x‐purinoceptors.
Uridine‐5′‐triphosphate (UTP) only induced a rapid and concentration‐dependent contraction of the rat bladder preparation, which was not desensitized by pre‐exposure to α,β‐meATP, suggesting that UTP responses were not mediated by the ‘classical’ P2X‐purinoceptor.
It is therefore concluded that both P2X‐ and P2Y‐purinoceptors, which mediate ATP‐induced contraction and relaxation, respectively, are present in rat bladder. Moreover, removal of epithelium did not affect ATP‐elicited contraction, whereas ATP‐induced relaxation was significantly augmented. These data suggest that P2x‐ and P2y‐ purinoceptors are localized in smooth muscle cells and that the relaxant response is probably modulated by excitatory factor(s) released by epithelial cells.
Vascular actions of thrombin receptor‐derived polypeptides: structure‐activity profiles for contractile and relaxant effects in rat aorta
Authors: Laniyonu Adebayo A. , Hollenberg Morely D. 
Published: July 2012

Using endothelium‐denuded and intact rat aortic rings, we have determined the contractile and relaxant structure‐activity profile for a series of thrombin receptor‐derived polypeptides (TRPs) based on the human and rat receptor sequences: SFLLR (P5), SFLLR‐NH2 (P5‐NH2) SFFLR (Rat P5), SFFLR‐ NH2 (Rat P5‐NH2), SFLLRNP (P7), SFLLRNP‐NH2 (P7‐NH2), SFFLRNP (Rat P7), SFFLRNP‐NH2 (Rat P7‐NH2), and SFLLRNPNDKYEPF (P14).
A contractile response to thrombin and the TRPs in the endothelium‐denuded aortic tissue was minimal or absent in preparations obtained from animals weighing less than 180 g (<6 weeks of age), but increased with animal size, plateauing in tissues derived from animals weighing between 320 and 420 g (about 9 to 14 weeks of age). In contrast, the contractile responses to KC1 and noradrenaline did not differ in the tissues and relaxant responses to the TRPs in endothelium‐intact aortic preparations were comparable for tissues obtained from either young (≤ 180 g) or older (≤ 320 g) animals.
The contractile response of the endothelium‐denuded preparation to thrombin and the TRPs showed marked cross‐desensitization: the relaxation response of the intact rings did not desensitize to the TRPs.
The relative potencies for the TRPs in the aortic contraction assay were comparable to those for the relaxation assay, but were distinct from the relative potencies we measured previously in a rat gastric longitudinal muscle contraction assay. Further, P5 behaved as a partial agonist in the aortic contraction assay, whereas it had been observed to be a full agonist in the gastric contraction assay.
The contractile activity of P5‐NH2 in endothelium intact aortic rings was low or absent, but in the presence of the nitric oxide synthase inhibitor, Nω‐nitro‐L‐arginine‐methyl ester (L‐NAME), the contractions in the intact preparation were equivalent to the response of the endothelium‐denuded preparation in the absence of L‐NAME.
The contractile response of the endothelium‐denuded aortic preparation to P5‐NH2 was inhibited by nifedipine and the kinase C antagonist, chelerythrine, but was resistant to the action of indomethacin, tetrodotoxin and the tyrosine kinase inhibitor, genistein.
We conclude that the receptor system for the TRPs in the aortic smooth muscle elements, responsible for the contractile response, is similar to the aortic endothelial cell receptor responsible for the relaxation response, but is distinct from the receptor that we have previously characterized in gastric longitudinal smooth muscle, results pointing to the presence of receptor subtypes in the vascular and gastric smooth muscle elements.
Prejunctional facilitatory α1‐adrenoceptors in the rat urinary bladder
Authors: Somogyi G.T. , Tanowitz M. , de Groat W.C. 
Published: July 2012

The effect of activation of α1‐adrenoceptors on acetylcholine (ACh) release and neurally evoked contractile responses induced by electrical field stimulation was investigated in smooth muscle strips from the rat urinary bladder.
Neurogenic contractions were facilitated by the α1adrenoceptor agonists, phenylephrine (PE) (2–128 μm) and methoxamine (2–128 μm) in a dose‐dependent manner. These agents also increased small amplitude spontaneous contractions of bladder strips and in 10% of strips increased basal tone. However, contractions elicited by exogenous ACh (1–10 μm) were not affected by α1agonists.
The magnitude of the PE facilitation was higher at lower frequencies (1–5 Hz) or at submaximal intensities of stimulation and at lower Ca2+ concentrations (0.5‐1 mM). The selective α1adrenoceptor antagonist, terazosin (TRZ) (0.05‐1 μm), competitively inhibited (pA2 value: 8.6) the PE facilitation of the neurally evoked contractions but not the PE induced increase of spontaneous contractions.
[3H]‐noradrenaline (NA) and [14C]‐ACh release evoked by electrical field stimulation were increased (140% and 173%, respectively) by 2μm PE. TRZ (0.05‐0.1 μm) blocked the PE facilitation of ACh release but not the facilitation of NA release. TRZ alone did not alter the release of ACh or NA nor the amplitude of the neurogenic contractions.
PE (2 μ) did not alter the basal release of ACh but did increase (by 180%) the basal release of NA. Desipramine (2 μm) blocked this effect of PE and also the PE‐facilitation of evoked ACh and NA release.
It is concluded that cholinergic terminals in the rat urinary bladder exhibit α1‐adrenoceptors which can facilitate the release of transmitter. However, under the conditions of our experiments it appears that cholinergic transmission is not modulated by α1 adrenergic mechanisms. Further studies are necessary to determine whether these receptors can be activated by endogenous noradrenaline released within the bladder.
Release of endothelium‐derived hyperpolarizing factor (EDHF) by M3 receptor stimulation in guinea‐pig coronary artery
Authors: Hammarström Anna K.M. , Parkington Helena C. , Coleman Harold A. 
Published: July 2012

The muscarinic receptor subtype(s) involved in the release of endothelium‐derived hyperpolarizing factor (EDHF) were studied in the guinea‐pig coronary artery by recording the membrane potential in the smooth muscle cells with intracellular microelectrodes.
Acetylcholine (ACh, pD2 6.68) was 10 times more potent than the M2 agonist, oxotremorine (pD2 5.65) and 500 fold more potent than the M1 agonist, McN‐A‐343 (pD2 3.95) in evoking the EDHF hyperpolarization.
The M3 muscarinic antagonist, 4‐diphenylacetoxy‐N‐methylpiperidine methiodide (4‐DAMP) was the most potent (pA2 9.5) in inhibiting the release of EDHF evoked by ACh, being more potent than pirenzepine (pA2 6.7), and AFDX‐116 (pA2 6.1) which preferentially block M1 and M2 receptors, respectively.
These results suggest that EDHF is released from the endothelium of the guinea‐pig coronary artery upon the activation of the muscarinic M3 receptor subtype.
Extended concentration‐response curves used to reflect full agonist efficacies and receptor occupancy‐response coupling ranges
Authors: Lew Michael J. 
Published: July 2012

An approach is described for generating extended agonist concentration‐response curves where the responses are unconstrained by the normal tissue maximum response. Functional antagonism is employed to hold the tissue state in the range where any change in stimulus can be translated into a measurable response.
The maximum response of these extended concentration‐response curves provides an index of intrinsic activity reflecting the agonist efficacy and the receptor occupancy‐response coupling range.
The use of this approach is illustrated with extended concentration‐response curves for noradrenaline (NA), vasopressin, acetylcholine (ACh), and 5‐methylfurmethide in the small mesenteric and tail arteries of the rat. Both NA and vasopressin can maximally activate the arteries, but the new protocol shows that NA can produce more cellular activation than vasopressin in the tail artery. Both ACh and 5‐methylfurmethide are full agonists but ACh has a higher intrinsic activity than 5‐methylfurmethide. The ACh muscarinic receptors in the mesenteric artery have a larger occupancy‐response range than the ACh muscarinic‐receptors in the tail artery, and the α‐adrenoceptors in the tail artery appear to have a larger occupancy‐response coupling range than those in the mesenteric artery.
This approach extends our ability to compare the efficacies of full agonists, and to compare the occupancy‐response coupling ranges of receptors that can normally maximally activate the assay tissue. This is achieved without the use of an irreversible antagonist and should be applicable to many receptors and pharmacological assay systems where responses are stable and functional antagonists are available.
Effects of the two enantiomers, S‐16257‐2 and S‐16260‐2, of a new bradycardic agent on guinea‐pig isolated cardiac preparations
Authors: Pérez Onésima , Gay Pilar , Franqueza Laura , Carron Rosalia , Valenzuela Carmen , Delpon Eva , Tamargo Juan 
Published: July 2012

The electromechanical effects of two enantiomers, S‐16257‐2 (S57) and S‐16260‐2 (R60), were studied and compared in guinea‐pig isolated atria and ventricular papillary muscles. The possible stereoselectivity of the interaction on the cardiac Na+ channel was analysed by comparing the effects of the two enantiomers on the onset and recovery kinetics of the frequency‐dependent Vmax block.
In spontaneously beating right atria, S57 and R60 (10−8 m‐10−4 m) exerted a negative chronotropic effect (pIC50 = 5.07 ±0.19 and 4.76 ±0.18, respectively) and prolonged the sinus node recovery time, this effect being more marked with S57. In electrically driven left atria, S57 decreased (P<0.05) contractile force only at 10−4 m and R60 at concentrations ≤5 × 10−5m, whereas in papillary muscles the negative inotropic effect appeared at concentrations > 10−5 m.
In papillary muscles driven at 1 Hz, S57 and R60 at concentrations higher than 5 × 10−6 m produced a concentration‐dependent decrease in the maximum upstroke velocity (Vmax) and amplitude of the cardiac action potential without altering the resting membrane potential or the action potential duration. S57 and R60 had no effect on the characteristics of the slow action potentials elicited by isoprenaline in ventricular muscle fibres depolarized in high K+ (27 mM) solution.
At 5 × 10−5 m, S57 and R60 produced a small tonic Vmax block. However, in muscles driven at rates between 0.5 and 3 Hz both enantiomers produced an exponential decline in Vmax (frequency‐dependent Vmax block) which augmented at higher rates of stimulation. The onset and offset rates of the frequency‐dependent Vmax block were similar for both drugs. Both S57 and R60 prolonged the recovery time constant from the frequency‐dependent block from 20.1 ±2.9 ms to 2–3 s.
At 5 × 10−5m, S57 and R60 shifted the membrane responsiveness curve in a hyperpolarizing direction.
It can be concluded that S57 and R60, the two enantiomers of the new bradycardic agent, produced a similar frequency‐dependent Vmax block which indicated that the interaction with the Na+ channel was not stereospecific. The analysis of the onset and offset kinetics of the frequency‐dependent Vmax block suggested that both enantiomers can be considered as Na+ channel blockers with intermediate kinetics, e.g., class IA antiarrhythmic drugs.