bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of benzodiazepines and non‐benzodiazepine compounds on the GABA‐induced response in frog isolated sensory neurones
Authors: Yakushiji Takashi , Fukuda Takemi , Oyama Yasuo , Akaike Norio 
Published: July 2012

The effects of benzodiazepines and non‐benzodiazepine compounds on the γ‐aminobutyric acid (GABA)‐induced chloride current (ICl) were studied in frog isolated sensory neurones by use of a concentration‐jump (termed ‘concentration‐clamp’) technique, under single‐electrode voltage‐clamp conditions. The drugs used were classified into four categories as follows: full benzodiazepine receptor agonists (diazepam, clonazepam, nitrazepam, midazolam, clotiazepam and etizolam), partial agonists (CL 218,872, Ro 16–6028, Ro 17–1812 and Ro 23–0364), inverse agonists (Ro 15–3505, FG 7142 and β‐CCE) and a benzodiazepine receptor antagonist, Ro 15–1788 (flumazenil).
All full agonists at concentrations of 3 × 10−6 m. or less increased dose‐dependently the peak amplitude of ICl elicited by 3 × 10−6 m. GABA to twice to three times larger than the control. However, no further augmentation of the GABA response was observed at concentrations of 1 × 10−5 m. or higher. Partial agonists also showed a dose‐dependent augmentation of the GABA response at concentrations ranging from 3 × 10−8 m. to 3 × 10−5 m., but their efficacies of augmentation of the GABA response were only about half or less of those of full agonists. Of the inverse agonists, β‐CCE had a unique dose‐dependent effect on the GABA response. β‐CCE reduced dose‐dependently the GABA response at concentrations of less than 3 × 10−6 m., but augmented it at concentrations of 3 × 10−5 m. and 6 × 10−5 m. The inverse agonists reduced dose‐dependently the GABA response. The benzodiazepine antagonist, flumazenil, slightly augmented the GABA response at concentrations between 3 × 10−7 m. and 3 × 10−5 m.
These results show clear differences in the effects on the GABA response between these four categories of compounds known to affect the benzodiazepine recognition site of the GABA/benzodiazepine receptor‐chloride channel complex. Our experimental system of frog isolated sensory neurones and a ‘concentration‐clamp’ technique appears to be useful for evaluating efficacy of compounds on responses mediated by the GABA/benzodiazepine receptor‐chloride channel complex.
5‐Hydroxytryptamine is a possible neurotransmitter of the non‐cholinergic excitatory nerves in the longitudinal muscle of rainbow trout stomach (Salmo gairdneri)
Authors: Kitazawa Takio 
Published: July 2012

The neurotransmitter of the non‐cholinergic excitatory nerves in the rainbow trout stomach was identified on the basis of the pharmacological properties of the contractile responses to transmural stimulation (TMS) and nicotine.
TMS caused tetrodotoxin‐sensitive contractions of rainbow trout stomach strips in a frequency‐dependent manner (0.5–50 Hz). Atropine (1 μm) significantly decreased the contractile response to low‐frequency stimulation (0.5–2 Hz), but did not affect that to high‐frequency stimulation (3–20 Hz).
The atropine‐resistant contractile response to TMS (20 Hz) was unaffected by hexamethonium (100 μm), phentolamine (5.4 μm), pyrilamine (1 μm), naloxone (1 μm) or substance P‐induced desensitization.
5‐Hydroxytryptamine (5‐HT, 3 nm‐3 μm) caused atropine‐resistant contractions in a concentration‐dependent manner. In the presence of atropine, methysergide (1 μm) decreased the contractile responses to TMS and 5‐HT.
Nicotine (3 μm‐500 μm) induced atropine‐resistant contractions that were completely abolished by tetrodotoxin or hexamethonium. Also methysergide inhibited the contractile responses to nicotine.
An acid extract of rainbow trout stomach exhibited atropine‐resistant contractions that were decreased by methysergide, in both rainbow trout stomach and guinea‐pig ileum longitudinal smooth muscle preparations.
The present results indicate that, in longitudinal muscle strips of the rainbow trout stomach, 5‐HT is one of the mediators (neurotransmitters) of the non‐cholinergic excitatory contractions induced by TMS and nicotine.
GABA receptors on the somatic muscle cells of the parasitic nematode, Ascaris suum: stereoselectivity indicates similarity to a GABAA‐type agonist recognition site
Authors: Holden‐Dye Lindy , Krogsgaard‐Larsen Povl , Nielsen Lone , Walker Robert J. 
Published: July 2012

The γ‐aminobutyric acid (GABA) receptors on the somatic muscle cells of Ascaris, which mediate muscle cell hyperpolarization and relaxation, have been characterized by use of intracellular recording techniques.
These receptors are like mammalian GABAA‐receptors in that the response is mediated by an increase conductance to chloride ions. The GABAA‐mimetic, muscimol, has a relative potency of 0.40 ± 0.02 (n = 3) compared to GABA.
The stereoselectivity of the GABA receptor on Ascaris is identical to that for the mammalian GABAA‐receptor, as determined from the relative potency of three pairs of enantiomers of structural analogues of GABA.
The most potent agonist is (S)‐(+)‐dihydromuscimol which is 7.53 ± 0.98 (n = 5) times more potent than GABA.
The Ascaris GABA receptor is not significantly blocked, at concentrations below 100 μm by the potent, competitive GABAA‐receptor antagonist, SR95531.
The Ascaris GABA receptor does not recognise agents that are known to block the GABA gated chloride channel in mammalian preparations such as t‐butylbicyclophosphorothionate (TBPS, 10 μm, n = 2) or the insecticide dieldrin (100 μm, n = 3).
GABAergic responses in Ascaris are not potentiated by pentobarbitone (100 μm, n = 3) or flurazepam (100 μm, n = 3).
The potencies of various GABA‐mimetics in the Ascaris preparation have been compared with their potency at displacing GABAA‐receptor binding in mammalian brain. Excluding the sulphonic acid derivatives of GABA, the correlation coefficient (r) between the potencies of compounds in the two systems is 0.74 (P < 0.01). The significance of this correlation is discussed.
The pharmacology of the Ascaris GABA receptor is discussed in relation to other invertebrate systems and the mammalian subclassification of GABA receptors.
In favour of the vesicular hypothesis: neurochemical evidence that vesamicol (AH5183) inhibits stimulation‐evoked release of acetylcholine from neuromuscular junction
Authors: Vizi E.S. 
Published: July 2012

The effects of optical isomers of vesamicol (2‐(4‐phenylpiperidino) cyclohexanol), an inhibitor of acetylcholine (ACh) storage, on stimulation‐evoked release of [3H]‐acetylcholine ([3H]‐ACh) from the neuromuscular junction have been studied in the region of the mouse hemidiaphragm which contains the motor endplates, and which can easily be loaded with [3H]‐choline. This method made it possible to detect exclusively the Cao‐dependent release of [3H]‐ACh in response to stimulation, and therefore to test the vesicular hypothesis.
(−)−Vesamicol was approximately 20 times more potent than (+)‐vesamicol in reducing stimulation‐evoked release of [3H]‐ACh.
4‐Aminopyridine, a potassium channel blocker, enhanced the release of ACh in response to stimulation, but failed to increase release from hemidiaphragm which had been pretreated with (−)−vesamicol.
The fact that (−)−vesamicol inhibited the release of [3H]‐ACh in response to electrical stimulation only when it was administered prior to the loading of the tissue with [3H]‐choline, and had no effect when the stores had already been filled with labelled [3H]‐ACh indicates that the stimulation‐evoked release of [3H]‐ACh is of vesicular origin and (−)−vesamicol has no effect on the release process. This is the first neurochemical evidence for the vesicular origin of stimulation‐evoked release of ACh from the neuromuscular junction.
Effects of putative activators of K+ channels in mouse pancreatic β‐cells
Authors: Garrino M.G. , Plant T.D. , Henquin J.C. 
Published: July 2012

The vasodilator and antihypertensive properties of pinacidil, cromakalim (BRL 34915), nicorandil and minoxidil sulphate may be due, at least in part, to their ability to open K+ channels in vascular smooth muscles. In this study, mouse pancreatic islets were used to determine whether these drugs affect insulin release by acting on K+ channels of β‐cells. Their effects were compared to those of diazoxide.
Diazoxide caused a dose‐dependent inhibition of insulin release by islets incubated with 15 mm glucose (93% at 100 μm). Pinacidil inhibited release by 36 and 72% at 100 and 500 μm, respectively. Cromakalim and nicorandil were less effective (35 and 25% inhibition at 500 μm). Minoxidil sulphate increased insulin release at 500 μm.
In the presence of 7 mm glucose and in the absence of Ca2+ (to avoid activation of Ca2+‐dependent K+ channels), 86Rb efflux from islet cells was increased by 100–500 μm pinacidil and 500 μm nicorandil, which were, however, less potent than diazoxide. Cromakalim was ineffective, whereas 500 μm minoxidil sulphate decreased the efflux rate. In the absence of glucose and presence of Ca2+, 500 μm cromakalim and minoxidil sulphate inhibited 86Rb efflux.
Like diazoxide, pinacidil (500 μm) abolished glucose‐induced electrical activity in β‐cells and hyperpolarized the membrane.
ATP‐sensitive K+ currents were studied in single β‐cells by the whole cell patch‐clamp technique. Pinacidil increased the current less than did diazoxide. In contrast, cromakalim and minoxidil sulphate decreased K+‐currents whilst nicorandil was without effect.
It is concluded that pinacidil, like diazoxide, inhibits insulin release from β‐cells by opening ATP‐sensitive K+ channels, whereas the smaller inhibitory effects of cromakalim and nicorandil may involve actions other than on K+ channels in these cells. Minoxidil sulphate potentiates glucose‐induced insulin release, probably by inhibiting ATP‐sensitive K+ channels. However, all these effects of the vasodilators are only seen at high concentrations and are thus unlikely to occur in vivo.
Myenteric 5‐HT‐containing neurones activate the descending cholinergic excitatory pathway to the circular muscle of guinea‐pig ileum
Authors: Jin Ji‐Guang , Neya Toshiaki , Nakayama Sosogu 
Published: July 2012

Participation of myenteric 5‐hydroxytryptamine (5‐HT)‐containing neurones in the ascending and descending pathways of the guinea‐pig isolated ileum was investigated in a new preparation. Transmural electrical stimulation of the longitudinal muscle‐myenteric plexus (LM‐MP) portion of the preparation caused ascending and descending contractions of circular or longitudinal muscle in the attached, intact segments situated orally or anally to the point of stimulation
All contractions to LM‐MP stimulation were abolished by tetrodotoxin (0.2 μm). The ascending and descending contractions of circular muscles were also abolished by atropine and inhibited to about 50% by hexamethonium. They were not affected by desensitization to substance P (SP) or by the SP antagonist, (D‐Pro2,D‐Trp7,9)‐substance P. The contractions of longitudinal muscles were inhibited by about 45% by hexamethonium and abolished by a combination of atropine with SP desensitization or the SP antagonist, (D‐Pro2,D‐Trp7,9)‐substance P.
Desensitization to 5‐HT, ICS 205–930 (1 μm) or cocaine (1 μm) reduced the descending contraction of circular muscle by 80–90%, without significantly affecting the ascending contraction. Methysergide (0.2 μm) failed to alter either contraction.
5‐HT desensitization, ICS 205–930 and cocaine only partially reduced the descending contraction of longitudinal muscle. A similar reduction of the ascending contraction (20–30%) was also observed. Methysergide had no effects on either contraction.
Contractions of either circular or longitudinal muscle produced by field stimulation of the intact segment were not significantly affected by any of the 5‐HT receptor antagonists tested.
The results imply that 5‐HT‐containing neurones, as interneurones, are involved mainly in the descending cholinergic excitatory pathway to the circular muscles.
α2‐Adrenoceptor agonists enhance vasoconstrictor responses to α1‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca2+
Authors: Xiao X.‐H. , Rand M.J. 
Published: July 2012

The α2‐adrenoceptor agonists TL99 (2‐(NN‐dimethyl)amino‐6,7‐dihydroxy‐1,2,3,4‐tetrahydronaphthalene) and UK14304 (5‐bromo‐6‐[2‐imidazoline‐2‐yl‐aminol]‐quinoxaline), in concentrations that are less than 1% of those producing vasoconstriction, enhance vasoconstrictor responses to noradrenaline and phenylephrine in isolated perfused preparations of the rat tail artery.
The enhancing effect was abolished when Ca2+ was absent and by the calcium channel blocking drug diltiazem.
α2‐Adrenoceptor agonists had no effect on the component of the responses to noradrenaline and phenylephrine that is attributable to mobilization of intracellular Ca2+, but enhanced the component attributable to influx of extracellular Ca2+.
These results suggest that the enhancing effect of α2‐adrenoceptor agonists on responses of the rat tail artery to α1‐adrenoceptor agonists involves an increase in Ca2+‐influx into smooth muscle cells through Ca2+ channels that are opened when α2‐adrenoceptors are activated.
Role of Na‐H exchange in the inotropic action of Bay K 8644 and of ouabain in guinea‐pig isolated atria
Authors: Ghysel‐Burton Josiane , Godfraind Théophile 
Published: July 2012

The inotropic effects of two concentrations of ouabain and of Bay K 8644 have been studied in isolated left atria of the guinea‐pig in physiological solutions at pH lowered from 7.4 to 6.0 and in the presence of ethylisopropylamiloride (EIPA) an inhibitor of Na+/H+ exchange. The low concentration of ouabain (300 nm) was chosen to saturate the high affinity binding sites (it occupied about 7% of the low affinity sites). The high concentration of ouabain saturated both high and low binding sites. Bay K 8644 evoked a positive inotropic effect of a magnitude similar to ouabain (300 nm).
When comparing the positive inotropic effects of equi‐effective concentrations of ouabain (300 nm) and of Bay K 8644 (100 nm), it was observed that extracellular acidification specifically depressed the inotropic effect of ouabain 300nm; the positive inotropic effect of the high concentration of ouabain (3 μm) was barely affected by extracellular acidification.
EIPA 10 μm depressed the positive inotropic effect of ouabain 300 nm, but did not affect the peak response to Bay K 8644. The depressant action of EIPA on the positive inotropic effect of ouabain was concentration‐dependent and was much more obvious on the effect of ouabain 300 nm than on ouabain 3 μm.
An increase in diastolic tension was evoked by 3 μm but not by 300 nm ouabain. This increase in tone was reduced dose‐dependently by EIPA (10–30 μm). It was also significantly reduced when the extracellular pH was equal to 6.4 or 6.0.
Ouabain (300 nm) evoked a gain in tissue Na and an equivalent loss in tissue K. Acidification of the extracellular pH down to pH 6.0 evoked a pH‐dependent reduction of Na gain but left K loss unaltered. EIPA 10, 20 and 30 μm evoked a significant reduction of Na gain without significantly affecting K loss.
Ouabain (3 μm) evoked a large gain in tissue Na and an equivalent loss of K. Tissue Ca content was also increased. Acidification of the extracellular pH from pH 7.4 to pH 6.9 evoked a significant reduction of Na and Ca gain; changes in tissue K were not significant. Acidification down to pH 6.0 increased reduction of Na and Ca gain, but not that of K loss which nevertheless became statistically significant.
These results show that tissue Na gain observed after inhibition of the sodium pump by ouabain may be related to activation of Na‐H exchange. They also indicate that blockade of Na‐H exchange selectively reduced the inotropic effect of ouabain in guinea‐pig atria resulting from interaction of the glycoside with high affinity binding sites. This confirms previous observations in rat heart.
Lithium amplifies inhibitions of inositol phospholipid hydrolysis in mammalian brain slices
Authors: Kendall David A. , Whitworth Paul 
Published: July 2012

We have examined the effects of lithium chloride (LiCl) on inhibitions of inositol phospholipid hydrolysis in guinea‐pig and rat brain slices by assessing the accumulation of [3H]‐inositol phosphates ([3H]‐InsP), in vitro.
In guinea‐pig and rat cerebral cortex slices the accumulation of total [3H]‐inositol phosphates due to the cholinoceptor agonist carbachol was inhibited by the excitatory amino acid l‐glutamate, but only when LiCl was present.
The effects of LiCl were time and concentration‐dependent. Significant inhibitions of the carbachol response by glutamate (in the presence of LiCl) being evident only after 20–30 min of stimulation at LiCl concentrations above 1.2 mm.
N‐methyl‐d‐aspartate (NMDA), in the absence of LiCl, enhanced the response to carbachol at low concentrations of the amino acid and inhibited the response at higher concentrations. In the presence of 5 mm LiCl, only the inhibitory phase was observed.
In rat cerebral cortex slices, aluminium fluoride inhibited [3H]‐InsP accumulation in the presence of carbachol, noradrenaline and a depolarising concentration of KC1 and these inhibitions were more marked when LiCl was present. The response to histamine was unaffected.
The data presented provide evidence that LiCl amplifies inhibitions of inositol phospholipid hydrolysis due to receptor and non‐receptor mediated stimuli, although the mechanism underlying the effect is, as yet, obscure.
Pharmacological and biochemical effects of the cardiotonic agent Org10325 in isolated cardiac and vascular tissue preparations
Authors: Shahid M. , Martorana M.G. , Cottney J.E. , Marshall R.J. 
Published: July 2012

The pharmacological and biochemical effects of a novel cardiotonic agent, Org10325 have been studied in isolated cardiac and vascular tissue preparations.
Org10325 produced concentration‐dependent (0.15–4.8 mm) positive inotropic, positive chronotropic and vascular relaxant responses in rabbit isolated papillary, atrial and aortic preparations, respectively. The maximal chronotropic effect (45%) was significantly less than the isoprenaline maximum. The inotropic effects of Org10325 were not modified by α‐ or β‐adrenoceptor blockade or by pretreatment with reserpine. Org10325 was at least 23 times more potent at relaxing aortic strips pre‐contracted with phenylephrine than with KCl.
Org10325 (74 μm) potentiated (10–14 fold) the positive inotropic effects of isoprenaline in rabbit isolated papillary muscles. Carbachol inhibited the positive inotropic effect of Org10325. Both the positive inotropic and vasorelaxant effects of Org10325 were accompanied by increases in cyclic AMP but not cyclic GMP.
In rat perfused heart preparation Org10325 increased phosphorylase a, cyclic AMP‐dependent protein kinase activities and stimulated phosphorylation of contractile proteins (troponin‐I and C‐protein).
Org10325 selectively inhibited the cyclic AMP hydrolytic activity of cyclic AMP high affinity cyclic nucleotide phosphodiesterase (PDE) isoenzymes, PDE III (IC50 65 μm) and PDE IV (IC50 71 μm), from rabbit cardiac ventricle. Weak inhibition (IC50 > 250μm) of PDE I and PDE II was observed.
The results show that the cardiac and vascular effects of Org10325 are mediated by an increase in cellular cyclic AMP due to inhibition of PDE III and PDE IV activities. However, in contrast to other PDE‐inhibitors Org10325 produced a marked increase in relaxation time of isolated papillary muscle suggesting the involvement of additional cyclic AMP‐independent mechanisms of action.
L‐NG‐nitro‐arginine and its methyl ester are potent inhibitors of non‐adrenergic, non‐cholinergic transmission in the rat anococcygeus
Authors: Hobbs Adrian J. , Gibson Alan 
Published: July 2012

The effects of l‐NG‐nitro‐arginine (l‐NOARG) and some other arginine analogues on non‐adrenergic, non‐cholinergic (NANC) relaxations of the rat anococcygeus muscle were investigated.
l‐NOARG (5–200 μm) produced concentration‐related inhibition of the NANC response; 100 μm l‐NOARG produced 90% inhibition.
l‐Arginine (5–200 μm) produced a concentration‐related reversal of the inhibitory effect of 20 μm l‐NOARG; a five fold excess of l‐arginine (100 μm) was required to obtain the maximum reversal of 90%. d‐Arginine (100 μm) produced no such reversal, but significant reversal was produced by l‐citrulline, l‐arginine‐l‐aspartate, l‐homoarginine and l‐arginine‐methyl‐ester (all at 100 μm).
l‐NG‐nitro‐arginine‐methyl‐ester (l‐NAME; 5–200 μm) also reduced NANC relaxations, with a potency similar to that of l‐NOARG; both l‐NOARG and l‐NAME were some ten times more potent than l‐NG‐monomethyl‐arginine (l‐NMMA). Like l‐NOARG, the effects of l‐NAME (20 μm) were reversed by 100 μm l‐ but not d‐arginine.
Neither l‐NOARG nor l‐NAME (both 20 μm) affected submaximal relaxations induced by 10 μm sodium nitroprusside or 20 μm hydroxylamine.
d‐NOARG, l‐NG‐tosyl‐arginine and l‐Nα‐(t‐butyl‐oxycarbonyl)‐NG‐nitroarginine (all at 100 μm) had no effect on NANC relaxations.
Thus, in the rat anococcygeus, l‐NOARG and l‐NAME are more potent than l‐NMMA as prejunctional inhibitors of NANC transmission. The reversibility of the effect of l‐NOARG by arginine analogues suggests that the NANC system of the anococcygeus shows similarities to the endogenous nitrate system recently described in the brain.
A study of the purinoceptors mediating contraction in the rat colon
Authors: Bailey S.J. , Hourani S.M.O. 
Published: July 2012

The effects of a number of purine analogues were examined on the rat isolated colon muscularis mucosae. Adenosine, adenosine 5′‐monophosphate (AMP), adenosine 5′‐diphosphate (ADP), adenosine 5′‐triphosphate (ATP), 2‐methylthioATP (MeSATP), adenosine 5′‐(2‐fluorodiphosphate) (ADPβF), adenosine 5′‐(β,γ‐methylene)triphosphonate (AM PPCP) and adenosine 5′‐(α,β‐methylene)triphosphonate (AMPCPP) each contracted the muscularis mucosae in the concentration range 1–100 μm.
MeSATP was the most potent purine agonist, with a threshold concentration for contraction of 0.05 μm and an EC50 of approximately 0.3 μm, and AMPCPP was less potent than ATP. The enantiomer of AMPPCP, l‐AMPPCP, was inactive at concentrations up to 100 μm.
The adenosine receptor antagonist 8‐(p‐sulphophenyl)theophylline (8‐SPT, 50 μm) produced approximately 50 fold shifts of the dose‐response curves to adenosine, AMP and AMPPCP, whereas those to ATP, MeSATP and substance P (SP) were unaffected. Intermediate shifts were observed for the dose‐response curves to ADP, AD$1βF and AMPCPP. With a lower concentration of 8‐SPT (10 μm) a dose ratio of approximately 11 was observed for the inhibition of the effects of both adenosine and AMPPCP.
ATP was rapidly degraded by the tissue to ADP, AMP and adenosine, AD$1βF was more slowly degraded to AMP and adenosine, and no significant degradation of AMPPCP was detected during 20 min incubation.
The results are consistent with the existence in the rat colon muscularis mucosae of a mixed population of purine receptors of P2Y and P1 types. The colon thus contains the first documented incidence of a P2Y‐receptor mediating contraction. The powerful inhibition by the P1‐purinoceptor antagonist 8‐SPT of the effects of AMPPCP suggests that its action in this tissue is mediated by P1‐purinoceptors, although 8‐SPT was more potent here than has previously been demonstrated.