bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions of benztropine, atropine and ketamine with veratridine‐activated sodium channels: effects on membrane depolarization, K+‐efflux and neutrotransmitter amino acid release
Authors: Erecińska Maria , Nelson David , Silver Ian A.
Published: July 2012

The effect of benztropine, atropine and ketamine on veratridine‐induced efflux of K+, membrane depolarization and release of amino acid neurotransmitters was investigated in the preparation of rat brain synaptosomes.

All three drugs inhibited in a concentration‐dependent manner the processes measured: the most effective compound was benztropine which exhibited an approximate Kd of 2 μm. The inhibition was not competitive in nature.

The veratridine titration curves in the presence of drugs were sigmoid with Hill coefficients of about 1.4.

At higher concentrations, benztropine, atropine and ketamine blocked uptake of amino acid neurotransmitters into synaptosomes.

It is postulated that benztropine, atropine and ketamine interfere with the veratridine‐activated influx of sodium into synaptosomes through voltage‐dependent channels by acting at the same site as local anaesthetics. Interactions at this site alter allosterically binding and action of veratridine. In addition, at higher concentrations the drugs interact with the carrier proteins for amino acid neurotransmitters and block their transport.
Short‐term desensitization of guinea‐pig taenia caecum induced by carbachol occurs at intracellular Ca stores and that by histamine at H1‐receptors
Authors: Hishinuma Shigeru , Uchida Masaatsu K.
Published: July 2012

In Ca‐free solution, the contractile response of guinea‐pig taenia caecum to 10−4 m carbachol was mediated through muscarinic receptors and was reduced time‐dependently by desensitization with 10−4 m carbachol, but not 10−4 m histamine. On the other hand, the response to 10−4 m histamine was shown to be mediated through H1‐receptors and to be reduced time‐dependently by desensitization with either 10−4 m histamine or 10−4 m carbachol.

The maximal K+ contraction was not changed by desensitization with carbachol or histamine. Thus, contractile proteins and voltage‐dependent Ca channels maintain their normal functions.

To study the coupling of Ca channel activity in cell surface membrane to receptor activation, the contractile responses elicited by carbachol and histamine added simultaneously with Ca to Ca‐free solution were measured. The response elicited by carbachol plus Ca was not changed by desensitization with carbachol, while that elicited by histamine plus Ca was reduced by desensitization with histamine. These results show that desensitization by carbachol occurs at a post‐receptor site, whereas that induced by histamine occurs at H1‐receptors.

After desensitization with carbachol, but not histamine, the contractile response to 5 × 10−2 m caffeine in Ca‐free solution was significantly reduced.

These results show that short‐term desensitization of guinea‐pig taenia caecum by carbachol is heterologous and occurs at intracellular Ca stores, while that induced by histamine is homologous and occurs at histamine H1‐receptors.
Analysis of the stimulative effect of thapsigargin, a non‐TPA‐type tumour promoter, on arachidonic acid metabolism in rat peritoneal macrophages
Authors: Ohuchi Kazuo , Sugawara Tadaki , Watanabe Masako , Hirasawa Noriyasu , Tsurufuji Susumu , Fujiki Hirota , Christensen S. Brøgger , Sugimura Takashi
Published: July 2012

At concentrations above 10 ng ml−1, the tumour promoter thapsigargin stimulates the release of radioactivity from [3H]‐arachidonic acid‐labelled macrophages harvested from rat peritoneal cavity.

The release of radioactivity from prelabelled macrophages was augmented more than additively when the cells were incubated in the medium containing both thapsigargin (10 ng ml−1) and other tumour promoters (10 ng ml−1), such as 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), teleocidin and aplysiatoxin.

Thapsigargin required extracellular Ca2+ for the stimulation of arachidonic acid release, while TPA did not.

Cytoplasmic free calcium level was increased by thapsigargin treatment but not by TPA treatment.

An inhibitor of protein kinases, H‐7 inhibited the effect of TPA dose‐dependently, whereas H‐7 did not inhibit that of thapsigargin.

These results suggest that thapsigargin stimulates arachidonic acid release by a mechanism different from that of TPA, viz by acting as a selective Ca2+ mobilizer, but not by activating protein kinase C as TPA does.
Dibromosulphophthalein: its pharmacokinetics and binding to hepatic cytosol proteins in rats with acute renal failure
Authors: Silberstein D.J. , Bowmer C.J. , Yates M.S.
Published: July 2012

The pharmacokinetics, biliary excretion and binding of dibromosulphophthalein (DBSP) to plasma proteins and hepatic cytosol proteins have been studied in male rats with glycerol‐induced acute renal failure (ARF).

The rate constants for hepatic uptake, efflux from liver to plasma and excretion into bile were all significantly decreased in rats with ARF. Furthermore, the plasma clearance of DBSP was also reduced.

The initial (0–10 min) and maximum biliary excretion rates of DBSP were both diminished in animals with ARF. The maximum excretion rate occurred between 5–10 min in control rats and 10–15 min in rats with ARF. However, there was no statistically significant change in the percentage dose recovered from bile after 30 min.

The plasma‐protein binding of DBSP was decreased in rats with ARF and this change was due to a significant reduction in the association constant for the primary binding sites.

The binding of DBSP to ligandin (Y protein) was reduced by about 38% in rats with ARF but no change was noted in binding to Z protein. Reduced binding to ligandin was accompanied by decreased total liver glutathione S‐transferase (GST) activity and a 36% reduction in the GST activity of ligandin.

The results support the contention that altered hepatic handling of cholephilic dyes in rats with ARF may be due to reduced binding to ligandin.
Vasodilator actions of acetylcholine, A23187 and bradykinin in the guinea‐pig isolated perfused heart are independent of prostacyclin
Authors: Stewart Alastair G. , Piper Priscilla J.
Published: July 2012

The involvement of prostacyclin (PGI2) in the vasodilator responses to acetylcholine (ACh), A23187 and bradykinin (Bk) has been investigated in guinea‐pig, isolated, Krebs‐perfused hearts.

ACh (0.01–10 nmol), A23187 (0.1–1.0 nmol) and Bk (0.3–10 pmol) each elicited dose‐related and shortlasting (∼2 min) reductions in perfusion pressure. Larger maximal responses were obtained in preparations with coronary vascular tone elevated by platelet‐activating factor (100 pmol) than in preparations at basal perfusion pressure.

Bk and A23187 elicited dose‐related increases in the generation of PGI2 as measured by its chemically‐stable breakdown product, 6‐oxo‐PGF1α. Indomethacin (2.8 μm) prevented both basal and the stimulated generation of 6‐oxo‐PGF1α, whereas the magnitudes of the vasodilator responses were unaffected.

Attempts to identify the release of vasodilator materials by on‐line superfusion bioassay of cardiac effluent were unsuccessful, indicating a possible role for a labile vasodilator such as endothelium‐dependent relaxing factor (EDRF). In addition, the inhibitors of EDRF action/production, mepacrine (3 μm) or diethylcarbamazine (300 μm), attenuated vasodilator responses to ACh without altering those to the endothelium‐independent vasodilator, verapamil (1 nmol).

Haemoglobin (10 μm) reduced vasodilator responses to ACh, Bk and verapamil and abolished those induced by A23187. Inhibition of the endothelium‐independent vasodilator, verapamil, was significantly less than that for the other compounds.

The present data indicate the existence of an indomethacin‐resistant vasodilator mechanism in the coronary microcirculation in response to ACh, A23187 and Bk. EDRF is a candidate for mediating these responses; however, a direct vasodilator action of these substances cannot be excluded.
Opioid modulation of non‐cholinergic neural bronchoconstriction in guinea‐pig in vivo
Authors: Belvisi M.G. , Chung K.F. , Jackson D.M. , Barnes P.J.
Published: July 2012

Opioid receptors have been demonstrated on sensory fibres in the vagus nerve. Non‐cholinergic (NC) neural bronchoconstriction in guinea‐pig is due to release of neuropeptides from sensory nerve endings. We have therefore studied the effect of opioids on this NC bronchoconstriction in the anaesthetized guinea‐pig.

Bilateral vagal stimulation (5 V, 5 ms, 10 Hz) caused reproducible bronchoconstriction in guinea‐pigs which was reduced by atropine (1 mg kg−1), but the NC component was unaffected by hexamethonium (10 mg kg−1).

NC bronchoconstriction was reduced by morphine in a dose‐dependent manner (ED50 = 132 μg kg−1 with a maximal inhibition of 79 ± 2.1% at 1 mg kg−1). Yohimbine (0.5 mg kg−1) did not alter the inhibitory effect of morphine (1 mg kg−1).

The inhibitory effect of morphine was completely reversed by naloxone (1 mg kg−1) which had no effect on NC bronchoconstriction. Propranolol (1 mg kg−1) significantly increased the NC bronchoconstrictor response but did not significantly alter the inhibition by morphine.

The selective μ‐opioid receptor agonist Tyr‐(d‐Ala)‐Gly‐(N‐Me‐Phe)‐Glyol (DAGOL) was significantly more potent than morphine with an ED50 of 5.4 μg kg−1 and complete inhibition at 100 μg kg−1. The δ‐agonist Tyr‐(d‐Pen)‐Gly‐Phe‐(d‐Pen) (DPDPE) was less potent than DAGOL with an ED50 of 28 μg kg−1 and a maximal inhibition of only 50 ± 5% at 100 μg kg−1. The κ‐receptor agonist, U‐50,488H had no inhibitory effect on the NC bronchoconstrictor response.

The bronchoconstrictor responses to exogenous substance P (25 μg kg−1) or acetylcholine (25 μg kg−1) were unaffected by morphine (500 μg kg−1).

We conclude that opioids inhibit the NC bronchoconstrictor response to vagal stimulation via an action on μ‐opioid receptors localized to sensory nerve endings in the airway.
Inhibition of field stimulation‐evoked relaxations in rat oesophageal smooth muscle by the calcium antagonist PN 200–110
Authors: Akbarali H.I. , Bieger D. , Triggle C.R.
Published: July 2012

The inhibitory effects of the 1,4‐dihydropyridine calcium channel antagonist, PN 200–110 (isradipine), on field stimulation‐evoked tetrodotoxin (TTX)‐sensitive and‐insensitive relaxations were studied in rat oesophageal smooth muscle of the tunica muscularis mucosae.

The TTX‐insensitive relaxation was inhibited by PN 200–110 in a stereoselective manner with the (+)−(S)‐isomer displaying a 1000 fold greater inhibitory potency than the (—)−(R) isomer. A similar potency was noted for inhibition of high K+‐evoked contractions.

TTX‐sensitive relaxations evoked by field stimulation and contractions elicited by the muscarinic cholinoceptor agonist, cis‐2‐methyl‐4‐dimethylamino‐methyl‐1,3‐dioxolane methiodide (cis‐dioxolane) were considerably less sensitive to inhibition by PN 200–110, although, again, stereoselectivity for PN 200–110 was apparent.

Pretreatment with (+)−(S)‐PN 200–110 resulted in a non‐competitive displacement of the Ca2+ concentration‐response curves obtained in the presence of either isotonic 50 mm KCl or cis‐dioxolane. The effect of K+ was 10 fold more sensitive than that of cis‐dioxolane.

The potency rank orders for inhibition of TTX‐insensitive field stimulation‐evoked relaxations and K+‐mediated contractions in a series of calcium channel antagonists were closely correlated; (+)−(S)‐PN 200–110 showing highest potency followed by nifedipine, verapamil, diltiazem, (—)−(R)‐PN 200–110.

It is concluded that TTX‐insensitive relaxations are dependent upon an influx of extracellular Ca2+ through potential‐operated calcium channels.
Similarity of relaxations evoked by BRL 34915, pinacidil and field‐stimulation in rat oesophageal tunica muscularis mucosae
Authors: Akbarali H.I. , Bieger D. , Ohia S.E. , Triggle C.R.
Published: July 2012

In the rat oesophageal tunica muscularis mucosae (TMM) the potassium channel openers, BRL 34915 and pinacidil, raised the threshold for concentration‐dependent K+ contractions, suppressed contractions evoked by field stimulation of the TMM in the presence of tetrodotoxin (TTX) and tetraethylammonium (TEA), and relaxed tonic contractions resulting from muscarinic cholinoceptor stimulation.

BRL 34915 and both (+)− and (−)‐pinacidil increased 86Rb efflux from tracer‐loaded tissues; nifedipine abolished this effect.

Relaxations produced by potassium channel openers were inhibited by a temperature drop from 37°C to 26.5°C, an increase in extracellular K+ concentration to 64 mm, and treatment with the calcium channel antagonist, nifedipine. The same treatments also blocked field stimulation‐evoked TTX‐insensitive relaxations.

It is concluded that field stimulation of rat oesophageal smooth muscle in the presence of cholinoceptor‐induced tone results in an increase in K+ permeability that is directly or indirectly coupled to Ca2+ influx through potential‐operated channels.
Effects of Ca2+ on the transient outward current of single isolated Helix central neurones
Authors: Tsuda Y. , Oyama Y. , Carpenter D.O. , Akaike N.
Published: July 2012

Single Helix neurones were studied under voltage‐clamp conditions with internal perfusion in order to examine the contribution of internal and external Ca2+ and the effects of 4‐aminopyridine (4‐AP) on the transient outward current (IA).

In Na+‐free snail Ringer, replacement of external Ca2+ ([Ca2+]o) with equimolar Co2+ reduced the maximum amplitude of IA and induced a shift of the steady‐state part of the IA inactivation curve (I‐V curve), in a positive direction along the voltage axis when the neurone was internally perfused with K‐aspartate.

In Ca2+‐free solutions, precipitation or chelation of internal Ca2+ ([Ca2+]i) by internal perfusion with KF or EGTA shifted the curve in a more negative direction without affecting the maximum amplitude of IA. Thus, the kinetics of IA are dependent not only upon [Ca2+]o, as previously suggested, but also upon [Ca2+]i.

In the presence of 4‐AP the I‐V curve for IA shifted in a hyperpolarizing direction and the maximal amplitude was reduced when the neurone was internally perfused with K‐aspartate. However, 4‐AP had little or no effect on the I‐V relationship of IA when the neurone was internally perfused with the Ca2+ precipitating or chelating agent, KF or EGTA. These results suggest that the actions of 4‐AP on IA are at least partly dependent upon [Ca2+]i.
Modulatory role of the vascular endothelium in the contractility of human isolated internal mammary artery
Authors: Schoeffter Philippe , Dion Robert , Godfraind Théophile
Published: July 2012

Endothelium‐dependent relaxant responses and modulation of contractile responses were investigated in human isolated internal mammary artery (HIMA), a vessel widely used for coronary bypass surgery.

Acetylcholine and ionophore A23187 (both 10 nm‐1 μm) elicited concentration‐dependent relaxations of precontracted HIMA. These relaxations were abolished after rubbing of the endothelium, they were inhibited by methylene blue and were insensitive to indomethacin.

Histamine at concentrations lower than 10 μm elicited an endothelium‐dependent, methylene blue‐sensitive relaxation of precontracted HIMA. This effect of histamine was inhibited by the H1‐receptor antagonist mepyramine. Bradykinin, noradrenaline and α2‐adrenoceptor agonists (in the presence of prazosin) did not relax unrubbed HIMA in which acetylcholine or A23187 were shown to be efficient.

Tissue levels of guanosine‐3′:5′‐monophosphate (cyclic GMP) were found to be significantly higher in unrubbed HIMA rings than in matched rubbed rings.

Methylene blue evoked a slow contraction in resting HIMA, and this contraction was significantly greater in unrubbed than in rubbed preparations. Also, methylene blue enhanced the contractile response of HIMA to noradrenaline and this potentiating effect was significantly greater in unrubbed than in rubbed preparations. Indomethacin induced a slow contraction, of similar magnitude in unrubbed and rubbed HIMA rings.

In resting HIMA, the concentration‐effect curve of noradrenaline‐induced contraction was significantly shifted to the left after rubbing of the endothelium, without change in the maximal responses. In unrubbed rings the EC50 value of noradrenaline was about 2 fold that in rubbed rings.

Histamine also contracted resting HIMA in a concentration‐dependent manner and in addition, it triggered rhythmic activity. This rhythmic activity was more prominent in unrubbed preparations and could be partially inhibited by indomethacin. The concentration‐effect curve of histamine‐induced contractions was displaced to the left after rubbing the endothelium, without changes in the maximal responses. The EC50 value of histamine in unrubbed rings was 4 to 9 fold that found in rubbed rings, depending on the level of tension taken into account for the concentration‐effect curve during rhythmic contractions.

In the presence of nifedipine (3 μm), noradrenaline‐induced contractions were not significantly altered, whereas histamine‐induced contractions were found to be inhibited by about 70%.

It is concluded that in HIMA, both spontaneous and stimulated endothelium‐dependent relaxing factor (EDRF) release may occur, and that basal EDRF can itself be responsible for the modulatory effect of endothelium on contractile responses.
Quinoxalinediones selectively block quisqualate and kainate receptors and synaptic events in rat neocortex and hippocampus and frog spinal cord in vitro
Authors: Fletcher E.J. , Martin D. , Aram J.A. , Lodge D. , Honoré T.
Published: July 2012

Two quinoxalinediones, FG9041 and FG9065, which had previously been shown to displace binding to the quisqualate receptor, were tested on rat neocortex and frog spinal cord in vitro against depolarizations induced by quisqualate, kainate and N‐methyl‐d‐aspartate (NMDA). In both preparations effects of quisqualate were reduced the most and those of NMDA the least.

The near unitary slopes of the Schild plots were consistent with a competitive type of interaction. pA2 values for FG9041 were estimated to be 6.6, 6.1 and 5.1 in frog cord and 5.9, 5.3 and about 4 in rat neocortex for quisqualate, kainate and NMDA antagonism, respectively. FG9065 gave equivalent pA2 values of 6.2, 5.6 and 4.5.

At concentrations, which were without effect on depolarizations induced by NMDA, FG9041 and FG9065 reduced or blocked synaptically‐evoked field potentials in hippocampal and neocortical slices superfused with normal magnesium‐containing medium. Since these synaptic components are also insensitive to NMDA antagonists, these results are consistent with their mediation by postsynaptic receptors of the quisqualate (or kainate) type.

By contrast, quinoxalinediones had only limited effects on spontaneous epileptiform activity seen in both neocortical and hippocampal preparations when superfused with magnesium‐free medium. These burst discharges were, however, abolished by NMDA antagonists.

In the frog spinal cord the early component of the dorsal root to ventral root reflexes was selectively reduced by FG9041 whereas NMDA antagonists reduced the longer latency components.

Our results suggest that the quinoxalinediones are likely to be useful pharmacological probes for elucidating the role of non‐NMDA receptors in the vertebrate central nervous system.
Effects of ryanodine on tension development in rat aorta and mesenteric resistance vessels
Authors: Julou‐Schaeffer G. , Freslon J.L.
Published: July 2012

The effects of ryanodine on contractile responses dependent either on intracellular Ca2+ release or on extracellular Ca2+ influx were studied in aorta and mesenteric resistance vessels of the rat.

In aorta, in the presence of extracellular Ca2+, pretreatment with ryanodine (10−5 m) did not modify contractile responses to noradrenaline (NA) (10−6 m) whereas in the absence of Ca2+, pretreatment with ryanodine reduced to about 25% the contractile response to NA (10−6 m) and totally abolished the transient contraction elicited by caffeine (5 × 10−2 m).

In mesenteric resistance vessels, ryanodine (10−5 m) had no effects on NA (10−5 m)‐induced tension in the presence of extracellular Ca2+ but totally abolished contractile responses to caffeine (10−2 m) in the absence of Ca2+.

In K+‐depolarized mesenteric resistance vessels, pretreatment with ryanodine (10−5 m) significantly enhanced contractile responses to Ca2+ concentrations higher than 10−4 m and 10−3 m for arteries depolarized with 30 mm and 40 mm K+ respectively. Concentrations of either diltiazem (6 × 10−7 m) or nifedipine (10−8 m) that abolished contractile responses to Ca2+ in depolarized arteries (K+, 40 mm) did not totally inhibit the enhancement of Ca2+‐induced contractions obtained in the presence of ryanodine.

Ryanodine did not modify the Ca2+ concentration‐effect relationships in mesenteric resistance vessels exposed to NA or arginine vasopressin.

These data are consistent with the hypothesis that ryanodine induces a release of Ca2+ from intracellular stores, resulting in a subsequent reduction of the amplitude of contractions dependent upon intracellular Ca2+ liberation. Furthermore, the ability of sarcoplasmic reticulum to buffer rises in cytoplasmic Ca2+ may be reduced in the presence of ryanodine, thereby accounting for the potentiation of contractile responses to Ca2+ in K+‐depolarized mesenteric resistance vessels.
A comparison of the differential effects of vasoactive intestinal peptide and peptide histidine isoleucine on the vascular and capsular smooth muscle of the dog spleen
Authors: Corder R. , Withrington P.G.
Published: July 2012

The actions of the two peptides, vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) have been compared to that of isoprenaline on the smooth muscle systems of the isolated blood‐perfused dog spleen.

Intra‐arterial injections of VIP and PHI caused graded increases in splenic arterial blood flow at constant perfusion pressure indicative of splenic arterial vasodilatation.

VIP was significantly more potent than PHI, with their respective molar ED50 values being 9.9 ± 3.7 and 830 ± 141 pmol (P < 0.002). VIP was approximately 10 and 200 times more potent than isoprenaline and PHI respectively.

The maximum reduction in splenic arterial vascular resistance was the same (P > 0.5) in response to intra‐arterial VIP and PHI, although both peptide maxima were significantly less (P < 0.05, 0.01 respectively) than that obtained with isoprenaline.

Small increases in spleen volume accompanied the splenic vasodilator responses to both peptides. They were probably passive in origin, secondary to splenic arterial vasodilatation.

The selective β2‐adrenoceptor antagonist, ICI 118,551, did not antagonize the splenic arterial vasodilator response to VIP or PHI but markedly attenuated the effect of isoprenaline.

These observations indicate that VIP and PHI, when either co‐released locally or present together in the systemic circulation, may exert a differential action on different components of the circulation.
Calcitonin gene‐related peptide desensitizes skeletal muscle arterioles to substance P in vivo
Authors: Öhlén Anders , Wiklund N. Peter , Persson Magnus G. , Hedqvist Per
Published: July 2012

Calcitonin gene‐related peptide (CGRP) was tested for possible interactions with the effects of substance P on rabbit skeletal muscle arterioles in vivo. Both CGRP and substance P dose‐dependently increased arteriolar diameter. However, pretreatment with CGRP made the arterioles insensitive to substance P, and also prevented the formation of aggregates of leukocytes and platelets normally seen after substance P. These results suggest that CGRP, in addition to its direct effects, may act as a modulator of the effects of substance P in neurogenic inflammation.
Selective blockade by nifedipine of ‘purinergic’ rather than adrenergic nerve‐mediated vasopressor responses in the pithed rat
Authors: Bulloch J.M. , McGrath J.C.
Published: July 2012

Nifedipine can attenuate pressor responses to sympathetic nerve stimulation both in the presence and in the absence of α‐adrenoceptor blocking agents.

In the presence of α,β‐methylene ATP, nifedipine produces only a small attenuation of the vasopressor response.

Nifedipine attenuates the vasopressor response produced by intravenous bolus administration of α,β‐methylene ATP.

The results suggest that the purinergic component of the vasopressor response to stimulation of the sympathetic outflow in the rat is subject to blockade by nifedipine, whereas the α‐adrenoceptor‐mediated response to co‐transmitter noradrenaline is relatively resistant.
The action of GABA receptor agonists and antagonists on muscle membrane conductance in Schistocerca gregaria
Authors: Murphy V.F. , Wann K.T.
Published: July 2012

The properties of postsynaptic γ‐aminobutyric acid (GABA) receptors in the extensor tibiae muscle of Schistocerca gregaria were studied by conventional electrophysiological recording techniques.

GABA and other active GABA receptor agonists produced rapid, dose‐dependent, reversible increases in membrane conductance.

In two microelectrode experiments the ED50 for GABA was approximately 1 mM. In three microelectrode experiments (assuming short cable theory conditions) the ED50 for GABA was 2.3 mM. The Hill coefficient for GABA estimated from the latter experiments was 1.4

The relative potency of muscimol/GABA at the ED50 for GABA was 1.36. 3‐Aminopropane sulphonic acid (3‐APS) and isonipecotic acid were weakly active, baclofen and piperidine‐4‐sulphonic acid (P4S) were inactive. Isoguvacine produced depolarizations and increases in conductance in preparations which hyperpolarized in response to GABA. These depolarizations were enhanced by both picrotoxin and pitrazepin although the increases in input conductance were depressed.

Picrotoxin (20 μm), (+)‐bicuculline (20–100 μm) and pitrazepin (1–10 μm) all reversibly antagonized GABA‐induced responses. Such antagonism was not competitive in the case of picrotoxin and (+)‐bicuculline but was competitive for pitrazepin. Schild plot analysis gave an average pA2 value of 5.5 for pitrazepin.

The significance of these results is briefly discussed.
Anti‐vasoconstrictor effects of the K+ channel opener cromakalim on the rabbit aorta—comparison with the calcium antagonist isradipine
Authors: Cook Nigel S. , Weir Sheila W. , Danzeisen Max C.
Published: July 2012

Contractile responses of rabbit aortic rings elicited by KCl‐depolarization, angiotensin II (AII), 5‐hydroxytryptamine (5‐HT) and noradrenaline (NA) have been investigated in the presence of cromakalim (BRL 34915) and isradipine (PN 200–110).

Above 10−6m, cromakalim inhibited contractile responses to low (≤32 mm) but not to higher KCl concentrations. The 5‐HT and AII concentration‐response curves were antagonized non‐competitively by cromakalim (10−7‐10−5m) and the maximal responses were inhibited by 40 and 55%, respectively.

Isradipine caused less inhibition of AII and 5‐HT contractile responses than cromakalim, and in the presence of isradipine (10−7 m), cromakalim was still able to antagonize further the contractions to AII in this vessel.

NA‐induced contractions were relatively insensitive to inhibition by cromakalim and isradipine, both drugs causing a small rightward shift of the NA concentration‐response curve. This result suggests that NA utilizes different Ca2+ pools from those involved in AII‐ and 5‐HT‐induced contractions of this vessel.

The sustained (tonic) part of the NA response was inhibited in a concentration‐dependent manner by cromakalim (10−7‐10−5 m), but not by isradipine.

In aortic rings partially depolarized with 3.5 × 10−2 m KCl, the ability of cromakalim, but not of sodium nitroprusside, atriopeptin III or hydralazine, to inhibit AII‐ and tonic NA‐induced contractions was abolished.

Antivasoconstrictor activity of cromakalim on the rabbit aorta appears to involve factors in addition to an indirect inhibition of Ca2+ entry through dihydropyridine‐sensitive Ca2+ channels.

The ability of cromakalim to open K+ channels and thereby modify the membrane potential would appear to underlie these antivasoconstrictor effects. This mechanism of action of cromakalim clearly differs from that of other vasodilators such as sodium nitroprusside and hydralazine.
The effect of temperature on the GABA‐induced chloride current in isolated sensory neurones of the frog
Authors: Ffrench‐Mullen J.M.H. , Tokutomi Naofumi , Akaike Norio
Published: July 2012

The effect of temperature on the kinetics of the activation and inactivation phases of γ‐aminobutyric acid (GABA)‐induced Cl− current (ICl) was examined in frog isolated sensory neurones.

The peak ICl was reversibly reduced on changing the temperature and temperature‐dependent coefficients were shown to exist, with the highest Q10 (1.58) occurring between 5–15°C.

At both room temperature (20°C) and 10°C, the GABA dose‐response curve was sigmoidal with a Hill coefficient of 2 and half‐maximal responses to GABA, Kd, of 1.3 × 10−5m and 1.1 × 10−5m, respectively. Thus, indicating no change in the binding affinity of GABA when the temperature was decreased.

At GABA concentrations greater than 10−5 m, both the activation and inactivation phases of the GABA‐induced ICl consisted of double exponentials, fast and slow components respectively, in the temperature range of 10 to 30°C.

The fast (ẗaf) and slow (ẗas) activation time constants decreased with an increase in temperature and increased with a reduction in temperature. With an increased temperature, the reduction in peak ICl was due to a reduction in the slow time constant with no significant change in the fast time constant.

Both the fast (T̈IF) and slow (ẗis) inactivation time constants were also increased by cooling to 10°C; heating to 30°C had little effect.

The concentration‐dependence (10−5 to 10−3 m) of the slow activation (ẗas) and inactivation (ẗis) time constants was unaltered by the change in temperature. Similarly, the lack of concentration‐dependence shown by the fast activation (ẗaf) and inactivation (T̈IF) time constants was unaltered by the temperature change.

From recordings made with ‘inside‐out’ patches, the probability of opening of the GABA‐induced Cl− channels showed a marked increase with cooling to 10°C compared to room temperature (20°C), with no change in channel conductance.

The change in the GABA‐induced ICl at different temperatures is, therefore, not due to changes in binding but to subsequent channel activation. Possible mechanisms whereby this occurs are discussed.
Effects of calcium channel antagonists and facilitators on beating of primary cultures of embryonic chick heart cells
Authors: Patmore Leslie , Duncan Greig P.
Published: July 2012

Primary aggregate cultures of embryonic chick heart have been used to investigate the effects of calcium channel antagonists and facilitators on myocardial contractility.

The number of aggregates showing movement was inhibited in a concentration‐dependent manner by calcium antagonists from different subgroups with negative log concentrations inhibiting movement in 50% of aggregates as follows: Class 1‐nisoldipine (7.20); Class 2‐verapamil (6.36), diltiazem (5.83); Class 3‐lidoflazine (5.68), pimozide (6.25).

The effects of the dihydropyridine facilitators Bay K 8644 and CGP 28392 on aggregate beating were investigated by evaluating the interaction between calcium channel facilitators and antagonists from the three subgroups of calcium antagonists. Concentrations of antagonists that inhibited beating in 85% of aggregates were used. Both Bay K 8644 and CGP 28392 reversed nisoldipine‐, diltiazem‐ or verapamil‐induced inhibition of beating.

Bay K 8644 was approximately 10 times more potent than CGP 28392 in reversing nisoldipine‐, diltiazem‐ or verapamil‐induced inhibition of beating.

For each facilitator the concentrations causing 50% reversal of inhibition of aggregate beating against the three antagonists were similar. There was little evidence for differential modulation by verapamil or diltiazem of the action of the dihydropyridine facilitators.

Bay K 8644 did not reverse lidoflazine‐ or pimozide‐induced inhibition of beating, indicating that these drugs may act at a site distinct from the dihydropyridine site on the calcium channel.
Kinetic and pharmacological properties of the GABA‐induced chloride current in Aplysia neurones: a ‘concentration clamp’ study
Authors: Ikemoto Yoshimi , Akaike Norio , Kijima Hiromasa
Published: July 2012

γ‐Aminobutyric acid (GABA) was applied by the ‘concentration clamp’ technique to isolated neurones of Aplysia. GABA induced a chloride current (ICl) due to activation of a single class of chloride‐channel.

The concentration‐response curve for the peak ICl gave an apparent dissociation constant of 6.4 × 10−5 m and a Hill coefficient of 0.88. The current‐voltage relationship was linear in the voltage range examined (‐40 to +10 mV).

The activation phase of the ICl could be fitted to a single exponential function and desensitization followed the sum of two exponential functions. The time constants of activation and desensitization decreased with increasing concentrations of GABA but were voltage‐independent. The recovery process from desensitization also followed the sum of two exponential functions.

As for the rate‐limiting step of the channel activation, the hyperbolic relationship between the activation rate and GABA concentration showed that the rapid binding assumption holds, suggesting that the isomerization step is rate‐limiting. The apparent channel closing rate constant was estimated to be 10s−1 from the ordinate intercept of the linear part of the above relationship at lower concentrations.

Muscimol and β‐alanine induced a ICl, which cross‐desensitized with that evoked by GABA. The GABA‐ICl was not enhanced by diazepam (10−6 m) or α‐chloralose (10−3m), in fact depressant effects were evident.

Pentobarbitone decreased the GABA‐ICl non‐competitively without altering activation or desensitization kinetics. The concentration‐inhibition curve gave a KD value of 8.9 × 10−5 m and a Hill coefficient of 1.0.

These results suggest that GABA activates a single class of Cl channel in Aplysia neurones, which have one binding site for the agonist. The GABA receptor‐Cl channel complex in Aplysia is pharmacologically and perhaps structurally different from that in vertebrates.
Ryanodine inhibits the Ca‐dependent K current after depletion of Ca stored in smooth muscle cells of the rabbit ileal longitudinal muscle
Authors: Sakai Takeshi , Terada Kazumasa , Kitamura Kenji , Kuriyama Hirosi
Published: July 2012

Effects of ryanodine on the membrane currents were investigated on dispersed smooth muscle cells of rabbit ileal longitudinal layer using voltage and patch clamp procedures.

With voltage clamp, membrane depolarization to 0mV from the holding potential of − 60 mV produced an inward Ca current (ICa) which was followed by transient and sustained outward currents (ITO and Iso, respectively). Prolonged depolarization of the membrane produced spontaneous oscillations of the outward current (oscillatory outward current; Ioo) on Iso.

Ryanodine (30 μm) modified neither the basal membrane current recorded at the holding potential (‐60 mV) nor Iso. Ryanodine inhibited both ITO and Ioo in a concentration‐dependent manner (IC50 = 5.5 and 4.5 μm, respectively, measured 12 min after application of ryanodine). These values were much higher than that observed in skeletal muscle for Ca release.

The time course of the ryanodine‐induced inhibition of Ioo was slow and the inhibition was irreversible. Caffeine (3mm) enhanced the amplitudes of ITO and Ioo in the presence of Ca, and only transiently enhanced Ioo in the absence of Ca. However, following application of 10 μm ryanodine, 3 mM caffeine did not increase Ioo.

Ryanodine (3–30 μm) slightly enhanced the amplitude of ICa evoked by depolarization pulses at potentials more negative than 0 mV but not that induced by larger depolarizations (positive potentials).

With patch clamp procedure, single Ca‐dependent K channel currents were recorded in cell free and cell attached configurations. Application of 30 μm ryanodine transiently enhanced the Ca‐dependent K current without any detectable changes in the amplitude of the single channel current recorded in the cell attached condition. In the inside‐out membrane patch, when the intracellular membrane side was superfused with 1 μm Ca buffered with 10 mM EGTA, bath application of 10 μm ryanodine had no effect on the Ca‐dependent K current.

It was concluded that both ITO and Ioo are generated by Ca released from intracellular stores, mainly sarcoplasmic reticulum. Ryanodine appears to open irreversibly the Ca channel in the store and to inhibit the Ca‐dependent K channel due to depletion of the stored Ca.
Influence of haemoglobin and erythrocytes on the effects of EDRF, a smooth muscle inhibitory factor, and nitric oxide on vascular and non‐vascular smooth muscle
Authors: Gillespie John S. , Sheng Hong
Published: July 2012

The relaxant action of endothelium‐derived relaxing factor (EDRF), the smooth muscle inhibitory factor (IF) isolated from the bovine retractor penis (BRP), nitric oxide (NO) and sodium nitroprusside (NaNP) on four vascular and non‐vascular smooth muscle preparations has been examined. Their sensitivity to EDRF, the IF and NO was the same, suggesting all might be NO. Sodium nitroprusside produced complete relaxation of the rat anococcygeus at low doses, suggesting an action additional to the intracellular release of NO.

Haemoglobin added to solutions of EDRF, activated IF or NO completely removed their relaxant properties, consistent with all three acting by virtue of NO.

Suspensions of red blood cells with a haemoglobin concentration equivalent to that used in the previous experiments were as effective as haemoglobin in abolishing the relaxant effect of EDRF or NO but were ineffective against the activated IF.

The similarity in sensitivity of a series of smooth muscles and the binding by haemoglobin are consistent with NO being the active principle of both EDRF and the acid activated IF. The abolition of the effect of EDRF by red blood cells (RBCs) is further confirmation for this hypothesis, but the ineffectiveness of RBCs against acid‐activated IF suggests that either the latter is not NO or that it is bound in a way which makes it unable to diffuse through cell membranes.
Membrane potential responses to ATP applied by pressure ejection in the longitudinal muscle of chicken rectum
Authors: Komori Seiichi , Ohashi Hidenori
Published: July 2012

Changes in membrane potential in response to local application of ATP by pressure ejection from a micropipette were recorded intracellularly from smooth muscle cells of the longitudinal muscle strip of chicken rectum.

The local application of ATP produced a membrane depolarization. The depolarizing response increased to a plateau of 33 mV with prolongation of the duration of pressure pulses which determines the amount of ATP ejected. The latency and the time required to reach a peak depolarization were not related to the pulse duration, and the shortest latency was 50 ms.

When the application of ATP was repeated at a short interval, the second and subsequent depolarizing responses were suppressed, and their latency and time to reach a peak were also increased; the muscle cells became desensitized to ATP. Recovery from the desensitization occurred slowly over a period of 60s.

Electrotonic potentials decreased in amplitude and time course during an ATP‐induced depolarization, indicating a decrease in membrane resistance.

The ATP‐induced depolarization was longer in the latency than an excitatory junction potential (e.j.p.) elicited by electrical field stimulation of the intramural nerves. The other variables such as amplitude, time to reach the peak and duration could not be matched with those of the e.j.p. at the same time.

The e.j.p. decreased in amplitude and duration during the ATP‐induced depolarization, and its initial amplitude and duration were restored immediately after termination of the ATP‐induced depolarization, as in the case of electrotonic potentials. The e.j.ps were recorded in the same manner as the control from the muscle cell which was in a state of desensitization to ATP.

The present results provide an argument against the hypothesis that ATP mediates the e.j.p. in the rectum of the chicken.
Regulation of P2y‐purinoceptor‐mediated prostacyclin release from human endothelial cells by cytoplasmic calcium concentration
Authors: Carter Thomas D. , Hallam Trevor J. , Cusack Noel J. , Pearson Jeremy D.
Published: July 2012

ATP and ATP analogues induced prostacyclin (PGI2) secretion from human cultured umbilical vein endothelial cells.

The threshold active concentration for ATP was ≤ 1 μm. The rank order of potency of analogues was 2‐chloroadenosine 5′‐triphosphate (2‐C1ATP) > 2‐methylthioadenosine 5′‐triphospate (2‐MeSATP) > ATP > ADP, while adenosine 5′‐(α,βfanethylene)triphosphonate, AMP and adenosine were inactive, indicating the presence of P2y‐purinoceptors.

In contrast to their actions on P2y‐receptors in guinea‐pig taenia coli, isopolar analogues of 2‐methylthioadenosine 5′‐(β,γ‐methylene)triphosphonate were less effective than ATP.

ATP and ATP analogues increased intracellular free calcium ions, [Ca2+]i, giving a rapid transient peak due predominantly to release from intracellular stores, followed by a maintained steady‐state elevated level due to influx.

The dose‐response curves for peak [Ca2+]i induced by ATP, 2‐C1ATP and 2‐MeSATP were very similar to those for PGI2 production.

Elevations of [Ca2+]i, above a threshold value of 0.8–1 μm, were necessary for PGI2 production in response to P2y‐receptor activation.

The dose relationships between PGI2 release and peak [Ca2+]i were equivalent whether [Ca2+]i was raised by ionomycin or via P2y‐receptor activation by ATP or 2‐ClATP, indicating that elevations of [Ca2+]i provide the major, if not the exclusive intracellular pathway for P2y‐purinoceptor‐mediated PGI2 synthesis.
Interactions between angiotensin II and α‐adrenoceptor agonists mediating pressor responses in the pithed rat
Authors: Grant T.L. , McGrath J.C.
Published: July 2012

The aim of the study was to investigate the interactions between angiotensin II (AII) and adrenoceptor‐mediated pressor responses in the pithed rat. Emphasis was placed on the effects of AII on blood pressure per se and the possibility of differential effects on α1 and α2‐adrenoceptor‐mediated pressor responses.

A low concentration of the angiotensin converting enzyme (ACE) inhibitor, teprotide (1 mgkg−1) lowered the resting diastolic blood pressure (BP) and attenuated only the second phase components of pressor responses to both α1‐ and α2‐adrenoceptor agonists. Infusion of AII (50ngkg−1 min−1) did not reverse the attenuating effect of teprotide and did not reliably restore the basal diastolic BP.

Although teprotide (10mgkg−1) did not produce a greater fall in diastolic BP than did the low dose (1mgkg−1), it attenuated the peak and second phase pressor responses to α1 and α2‐adrenoceptor agonists but had no effect on pressor responses to AII or 5‐hydroxytryptamine (5‐HT). Infusion of AII reversed the effects of teprotide (10mgkg−1) provided that rats were pretreated with flurbiprofen (5mgkg−1), confirming that the depressor effects of the higher dose of teprotide are AII‐dependent but that demonstration of this was complicated by products of cyclo‐oxygenase.

The AII‐receptor antagonist, saralasin (4μgkg−1 min−1) attenuated α1‐ and α2‐adrenoceptor‐mediated pressor responses in a manner similar to that of teprotide (10mgkg−1), suggesting that in this pithed rat model the α‐adrenoceptor‐mediated responses were selectively facilitated by endogenous AII.

Infusion of AII (50ngkg−1 min−1) over a 60min period did not produce a pressor response in the absence of other drugs but did facilitate pressor responses to α‐adrenoceptor agonists. This confirms that AII can modulate α‐adrenoceptor‐mediated responses independently of basal blood pressure.

Overall the results indicate a facilitatory role for endogenous AII on α‐adrenoceptor‐mediated pressor responses. This is discussed in relation to the failure to demonstrate this convincingly under similar conditions on sympathetic nerve‐mediated pressor responses.
Effects of the myocardial‐selective α1‐adrenoceptor antagonist UK‐52046 and atenolol, alone and in combination, on experimental cardiac arrhythmias in dogs
Authors: Uprichard Andrew G.C. , Harron Dean W.G. , Wilson Richard , Shanks Robin G.
Published: July 2012

Adrenaline‐induced arrhythmias in anaesthetized dogs respired with halothane were attenuated in 3 groups of 6 dogs by either UK‐52046, 3.8 ± 1.4μgkg−1 (mean ± s.e.mean), atenolol 14.6 ± 2.1 μgkg−1, or a combination containing equal amounts of the two drugs of 0.36 ± 0.1 μgkg−1. The pressor response to adrenaline was reduced (P < 0.01) by UK‐52046 but not by atenolol or the combination of both drugs.

In a group of 6 dogs with multiventricular ectopic beats 24 h after coronary artery ligation (CAL), UK‐52046, 32μgkg−1, increased the number of sinus beats in each 5min period from 137 ± 47 to 662 ± 99 (P < 0.01); this was associated with a significant (P < 0.01) fall in blood pressure. Atenolol in doses of up to 800μg kg−1 had no effect.

UK‐52046, 3.7 ± 1.4μgkg−1, prevented adrenaline‐induced arrhythmias 3–4 days after CAL in 6/6 conscious dogs; atenolol in doses of up to 100μgkg−1 produced an 84.4 ± 7.4% reduction in the number of ventricular ectopic beats. A combination containing 3.7 ± 1.1 μgkg−1 of each drug prevented the arrhythmia in 6/6 dogs. The pressor response to adrenaline was attenuated (P < 0.05) by UK‐52046, but resting blood pressure was unaffected by the different treatments. An increase (P < 0.01) in heart rate was associated with both UK‐52046 and the combination.

Neither UK‐52046 (doses up to 64μgkg−1) nor atenolol (up to 800μgkg−1) had any effect upon ouabain‐induced arrhythmias in 2 groups of 6 anaesthetized dogs.

In a study of the early (1a/1b) arrhythmias of acute myocardial ischaemia, the total number of ventricular ectopic beats occurring within 30min of CAL was not reduced by 4μgkg−1 UK‐52046 but fell (P < 0.01 compared with placebo) after 8μgkg−1 [median values with ranges for placebo, 4μgkg−1 and 8μgkg−1 respectively 190 (4–674), 246 (9–1204) and 12 (1–154)]. Both doses of UK‐52046 were associated with significant falls in blood pressure.

The arrhythmias produced by programmed electrical stimulation were studied in 2 groups of 6 conscious dogs, 7–30 days after CAL. With placebo, 4/6 dogs remained unchanged and 2 died: UK‐52046 prevented arrhythmias in 2/6, 2 remained unchanged and 2 died (P = 0.29). Compared with placebo, blood pressure fell with doses greater than 4μgkg−1.

These results indicate antiarrhythmic effects of UK‐52046 in a number of experimental models and suggest an enhanced role of α‐receptors in the genesis of ischaemia‐related arrhythmias. In several of the models used, UK‐52046 produced haemodynamic changes in keeping with peripheral α‐adrenoceptor antagonism.