bluuebunny/crossref_metadata_2025 huggingface dataset:
Restricted usefulness of tetraethylammonium and 4‐aminopyridine for the characterization of receptor‐operated K+ ‐channels
Authors: Drukarch B. , Kits K.S. , Leysen J.E. , Schepens E. , Stoof J.C.
Published: July 2012

Recently, we suggested that the D2‐dopamine receptor involved in the inhibition of evoked [3H]‐acetylcholine release from rat striatum is coupled to K+‐channels.

In the present study, an attempt was made to elucidate further the role of these K+‐channels, using the K+‐channel blocking agents tetraethylammonium and 4‐aminopyridine. With a superfusion method, the effects of both drugs on the D2‐dopamine receptor‐mediated inhibition of the electrically evoked release of [3H]‐acetylcholine from rat striatal tissue slices was investigated.

Both tetraethylammonium (30 mM) and 4‐aminopyridine (0.1 mM) significantly stimulated the electrically evoked release of [3H]‐acetylcholine and completely abolished the effect of the selective D2‐receptor agonist LY 171555 (1 μm) on evoked acetylcholine release. In addition, tetraethylammonium (0.03–30 mM) and 4‐aminopyridine (0.003‐1 mM) strongly increased the basal (non‐evoked) release of radioactivity in a concentration‐dependent manner. The results suggest that the effect of the drugs on the basal release of radioactivity and on the electrically evoked release of acetylcholine cannot exclusively be explained by their action on K+‐channels.

Furthermore, with the use of a receptor binding assay, data were obtained on the affinity of tetraethylammonium and 4‐aminopyridine for D2‐receptors and various other neurotransmitter recognition sites. At concentrations in which both drugs are known to block K+‐channels, they were found to inhibit the specific binding of selective radioligands to their respective recognition sites.

It is concluded that due to their ‘side‐effects’, both tetraethylammonium and 4‐aminopyridine are of only limited value in the investigation of the alleged interaction between neurotransmitter receptors and K+‐channels.
Endothelin induces an increase in renal vascular resistance and a fall in glomerular filtration rate in the rabbit isolated perfused kidney
Authors: Cairns Hugh S. , Rogerson Mary E. , Fairbanks Lynette D. , Neild Guy H. , Westwick John
Published: July 2012

The effects of endothelin infusion on renal vascular resistance (RVR), glomerular filtration rate (GFR) and the interaction with locally generated endothelium‐derived relaxant factor (EDRF) were studied in the rabbit isolated perfused kidney (IPK). For comparison the effects of infusions of angiotensin II (AII) and noradrenaline (NA) were also assessed.

Each kidney was perfused at a constant rate of 10 ml min−1 and alterations in RVR determined by measuring changes in perfusion pressure. GFR was determined by the clearance of [51Cr]‐EDTA, using timed urine collections.

Endothelin (10−11‐10−9 M) produced a dose‐related increase in RVR. Endothelin was approximately 30 times more potent in molar terms than AII and 500 times more than NA at inducing a 50 mmHg increase in perfusion pressure.

Endothelin appeared to be a weak inducer of EDRF release in the IPK as EDRF inhibitors methylene blue (10 μm) or haemoglobin (10 μm) only slightly augmented the increase in RVR at a given concentration of endothelin. In contrast the effect of NA on RVR was significantly increased by methylene blue (10 μm) whereas that induced by AII was not affected.

Endothelin infusion produced a significant, dose‐dependent decrease in GFR of the IPK, contrasting with an increase in GFR during AII infusion and a minimal effect of NA on GFR. This supports evidence that AII is predominantly a constrictor of efferent glomerular arterioles and that NA constricts both afferent and efferent glomerular vessels. We suggest that the vasoconstrictive effect of endothelin in the kidney is predominantly preglomerular, which explains its effect on GFR.
Electrophysiological effects of OPC‐88117, a new antiarrhythmic agent on papillary muscles and single ventricular myocytes isolated from guinea‐pig hearts
Authors: Toyama Junji , Kodama Itsuo , Honjo Haruo , Kamiya Kaichiro
Published: July 2012

The effects of OPC‐88117, a new antiarrhythmic agent, on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea‐pig hearts.

In papillary muscles, OPC‐88117 above 3 × 10−6 m caused a dose‐dependent prolongation of action potential duration (APD).

OPC‐88117 above 3 × 10−5 m caused a significant decrease in the maximum upstroke velocity () of the action potential without affecting the resting membrane potential. The inhibition of was enhanced at higher stimulation frequencies.

In the presence of OPC‐88117, trains of stimuli at rates ≥ 1.0 Hz led to a use‐dependent inhibition of with rapid onset. The time constant for the recovery of from the use‐dependent block was 456 ms.

The curves relating membrane potential and were shifted by OPC‐88117 to the direction of more negative potentials (9mV at 10−4 M).

In single ventricular myocytes treated with OPC‐88117 (1–3 × 10−4 M), the of test action potentials preceded by conditioning clamp pulses to 0mV was decreased progressively as the clamp pulse duration was prolonged.

These findings suggest that the primary electrophysiological effect of OPC‐88117 on the cardiac muscle cell is prolongation of APD (Class III action) and that at high concentrations, it may also possess a lignocaine‐like sodium channel inhibitory effect (Class I action).
Effects of OPC‐88117, a new antiarrhythmic agent, on the electrophysiological properties of rabbit isolated hearts
Authors: Nezasa Yasuko , Kodama Itsuo , Toyama Junji
Published: July 2012

Effects of a new antiarrhythmic agent, OPC‐88117, on the conduction properties and excitability of Langendorff‐perfused rabbit hearts were compared with those of lignocaine.

OPC‐88117 above 10−5 m caused a significant prolongation of atrio‐His bundle conduction time (A‐H interval) as well as His bundle‐ventricular conduction time (H‐V interval). Lignocaine above 10−5 m caused a similar prolongation of H‐V interval with a minimum change of A‐H interval. The conduction time from His bundle stimulus to the left ventricle (St‐LV) at a low frequency (1 Hz) was also prolonged by these drugs around 10−4 M.

OPC‐88117 above 3 × 10−6 m prolonged the effective and functional refractory periods of His bundle (ERPHB, FRPHB) as well as the effective refractory period of left ventricular muscle (ERPVM) in a dose‐dependent manner. ERPHB, FRPHB and ERPVM were, shortened by low concentrations of lignocaine (3 × 10−6‐10−5 M), but were prolonged by high concentrations (3 × 10−5‐10−4 M).

Lignocaine (3 × 10−6‐10−4 M) induced an upward displacement of the His bundle refractory curve, indicating a greater intraventricular conduction delay for premature excitation. In experiments with OPC‐88117, such an upward displacement was observed only at 10−4 M.

These results suggest that the primary electrophysiological effect of OPC‐88117 is a lengthening of ventricular refractoriness, and that at high concentrations it may also exert lignocaine‐like inhibition of ventricular conduction.
2‐Chloroadenosine attenuates kainic acid‐induced toxicity within the rat striatum: relationship to release of glutamate and Ca2+ influx
Authors: Arvin B. , Neville L.F. , Pan J. , Roberts P.J.
Published: July 2012

The mechanism by which 2‐chloroadenosine (2‐chloroado) exerts a neuroprotective action against the excitotoxic effect of kainic acid (KA) when injected into the rat striatum was investigated.

Histological examination two weeks after a single injection of KA (2.2 nmol) into rat striatum revealed widespread neuronal damage. Co‐injection of 2‐chloroado (6–25 nmol) with the neurotoxin afforded dose‐dependent neuroprotection. This effect was reversed by administration of an equimolar concentration of the adenosine receptor antagonist theophylline.

Both K+ (30 mM) and KA (1 mM) enhanced the release of endogenous glutamate from guinea‐pig purified cerebrocortical synaptosomes in a predominantly (approximately 70%) Ca2+‐dependent manner. 2‐Chloroado (10 nM‐1 μm) inhibited the release of glutamate evoked by both KA and K+. These effects were partially reversed by the selective A1‐adenosine receptor antagonist 8‐cyclopentyltheophylline (CPT) (1 μm).

Crude rat cortical synaptosomes were loaded with the fluorescent calcium indicator quin‐2 and Ca2+ influx monitored following two successive depolarising stimuli (30 mM K+; ′S1′ and ′S2′). 2‐Chloroado (10 nM‐1 μm) produced a dose‐dependent reduction in the S2:S1 ratio when added before the S2 period of stimulation. This effect was reversed by 1 μm theophylline. However, KA (1 mM) failed to enhance Ca2+ influx in the same preparation.

These results suggest that the anti‐excitotoxic action of 2‐chloroado is mediated primarily through a specific presynaptic receptor mechanism involving reduction of transmitter glutamate release, possibly occurring through an inhibition of Ca2+ influx.
A dual model for cardiac arrhythmias: coexistence of re‐entry and abnormal automaticity and effects of antiarrhythmic agents
Authors: Wu Kuei‐Meng , Hunter Thomas , Proakis Anthony
Published: July 2012

We have developed a dual model for arrhythmia in anaesthetized dogs. The model consists of an inducible re‐entrant atrial tachycardia and spontaneous ventricular ectopies in the same heart.

The model for re‐entrant atrial tachycardia was created by crushing the right atrium longitudinally in the intercaval region and transversely in the front free wall parallel to the atrioventricular groove. Ventricular abnormal automaticity was produced by prior (20 ∼ 24 h) left anterior descending coronary artery occlusion. The ventricular arrhythmia was partially suppressed during rapid pacing‐induced atrial tachycardia and resumed after atrial re‐entry was terminated.

Mapping experiments indicate that the atrial tachycardia was due to circus movement occurring in the tissue around the tricuspid ring. This re‐entrant circuit was identical to that induced in the model created by the incision method.

Clofilium (0.75 mg kg−1, n = 5) increased the cycle length of atrial re‐entry by 14 ± 4% from 139 ± 12 to 159 ± 18 ms (P < 0.05). Flecainide (1.8 ± 0.9 mg kg−1, n = 5) prolonged the cycle length of the tachycardia by 114 ± 57% from 158 ± 11 to 332 ± 66 ms (P < 0.05).

Both drugs terminated the atrial arrhythmia, but re‐entry could be reinduced only in flecainide‐treated dogs. Flecainide reduced ventricular ectopies by 89 ± 19%, whereas clofilium did not change ventricular abnormal automaticity or maximum pacing cycle length that is necessary to overdrive the ventricle fully.

These data indicate that the dual model provides coexisting arrhythmias of different mechanisms in the same heart and that Class I and Class III anti‐arrhythmic drugs may be differentiated from each other by the distinct patterns of pharmacological activities produced in this test system.
Vasopressin and the pathogenesis of chronic renal failure
Authors: Brooks David P. , Solleveld Henk A. , Contino Lisa C.
Published: July 2012

Partial (5/6) renal ablation was performed in Long Evans rats treated with vehicle or a vasopressin V1‐receptor antagonist, in control Long Evans rats, and in homozygous Brattleboro rats which lack endogenous vasopressin.

In control and vasopressin‐blocked Long Evans rats, 3 weeks following partial renal ablation, systolic blood pressure was 215 ± 5 and 199 ± 9 mmHg and, urinary protein excretion was 54 ± 4 and 50 ± 3mg day−1, respectively.

The pressor response to exogenous vasopressin was significantly (P < 0.05) reduced in rats treated with the V1‐receptor antagonist (ED50mmHg 5.0 ± 1.6 vs. 0.09 ± 0.01 μg kg−1).

In control Long Evans and in Brattleboro rats, 3 weeks following renal ablation, systolic blood pressure was 204 ± 10 and 191 ± 7 mmHg, and urinary protein excretion was 97 ± 27 and 71 ± 5 mg day−1, respectively.

Histological examination of the remaining kidney tissue demonstrated significant glomerular hyalinization following renal ablation but no differences between any of the groups.

The data indicate that neither vasopressin nor the urinary concentrating mechanism is likely to be involved in the hypertension and proteinuria associated with partial renal ablation.
Time‐dependent effects of theophylline on myocardial reactive hyperaemias in the anaesthetized dog
Authors: Gidday Jeffrey M. , Esther John W. , Ely Stephen W. , Rubio Rafael , Berne Robert M.
Published: July 2012

The effects of a loading dose of theophylline (5 mg kg−1 i.v.) on the hyperaemias resulting from short‐term (15 and 30 s) interruptions in coronary blood flow and intracoronary adenosine were studied at given intervals over a 2 h period in the anaesthetized dog.

These hyperaemic responses were affected differently by theophylline and each effect was time‐dependent. The reactive hyperaemic response progressively decreased after drug delivery, reaching 46% of control at 2 h. In contrast, after a maximal attenuation to 23% of control 5 min after theophylline, the hyperaemia resulting from intracoronary adenosine progressively increased over the same period, reaching 64% of control 2 h after the loading dose.

Two‐compartment model results based on plasma theophylline measurements and the time course of theophylline accumulation in pericardial infusates, suggested that complete drug distribution throughout the heart may require at least 20 min following a single intravenous dose.

If it is assumed that theophylline blocks coronary vascular adenosine receptors, these pharmacokinetics are consistent with the time‐dependent pattern of response attenuation we observed for the adenosine‐induced hyperaemias, but they cannot entirely explain the pattern of response attenuation observed for the occlusion‐induced hyperaemias. The continued increase in attenuation of this response after complete drug distribution suggests an additional pharmacodynamic action of theophylline.

We conclude that a single therapeutic dose of theophylline results in distinct time‐dependent pharmacological effects with respect to the ability of the coronary vasculature to dilate in response to temporary interruptions in oxygen supply and in response to exogenously administered adenosine. These effects deserve consideration in both experimental studies in which adenosine antagonists are used to assess adenosine action in vivo, and in clinical practice where theophylline pharmacotherapy for pulmonary disorders is commonplace.
Effects of various neuropeptide Y/peptide YY fragments on electrically‐evoked contractions of the rat vas deferens
Authors: Grundemar Lars , Håkanson Rolf
Published: July 2012

The effects of various neuropeptide Y (NPY) and peptide YY (PYY) fragments on electrically‐evoked twitches in the rat isolated vas deferens were studied and compared with the effects of full length NPY and PYY. The aim was to identify the shortest NPY/PYY fragments that are capable of suppressing the contractions.

NPY (1–36) and C‐terminal fragments of NPY (from 11–36 to 22–36) suppressed the electrically‐evoked twitches in a concentration‐dependent manner. On the whole there seemed to be a gradual lowering of the pIC50 values with progressive shortening of the NPY fragments (except for fragments 16–36 and 22–36 that had rather high pIC50 values). NPY 23–36, 24–36 and 25–36 suppressed the twitches at high concentrations (3 μm). NPY 26–36 was without effect as were C‐terminal carboxy‐deaminated NPY and glycine extended NPY (NPY‐Gly‐Lys‐Arg).

PYY (1–36) and C‐terminal fragments of PYY (from 11–36 to 23–36) suppressed the electrically‐evoked twitches in a concentration‐dependent manner. PYY 1–36 was more potent than any of the fragments. There was a tendency for shorter fragments to have lower pIC50 values. PYY 24–36 and 25–36 suppressed the twitches at high concentrations (3 μm). PYY 26–36 was without effect.

The findings suggest that the 12 C‐terminal amino acid residues of NPY and PYY are the minimum length required to activate the Y2‐receptor.
Regional haemodynamic changes during oral ingestion of NG‐monomethyl‐l‐arginine or NG‐nitro‐l‐arginine methyl ester in conscious Brattleboro rats
Authors: Gardiner Sheila M. , Compton Alix M. , Bennett Terence , Palmer Richard M.J. , Moncada Salvador
Published: July 2012

Homozygous Brattleboro (i.e. vasopressin‐deficient) rats were chronically instrumented with pulsed Doppler probes and intravascular catheters to permit continuous monitoring of regional haemodynamics. Over a 9 h period, rats drinking water showed no systematic changes in heart rate or mean arterial blood pressure although renal, mesenteric and hindquarters vascular conductances fell. These changes showed diurnal rhythyms, probably related to the nocturnal habits of rats. In separate groups of animals spontaneous oral ingestion of NG‐monomethyl‐l‐arginine (l‐NMMA; 1mg ml−1) or NG‐nitro‐l‐arginine methyl ester (l‐NAME; 0.1 mg ml−1) caused marked hypertension but no significant bradycardia. Compared to control animals, rats drinking l‐NMMA for 9 h showed significantly greater mesenteric and hindquarters vasoconstrictions, and rats drinking l‐NAME showed greater vasoconstrictions in all 3 vascular beds.
The effects of acute and chronic lithium treatment on pilocarpine‐stimulated phosphoinositide hydrolysis in mouse brain in vivo
Authors: Whitworth P. , Heal D.J. , Kendall D.A.
Published: July 2012

Measurements were made of the in vivo formation of inositol phosphates in the brains of C57/B1/601a mice treated acutely or chronically with lithium chloride (LiCl).

A single injection of LiCl (10 m Equiv kg−1, s.c.) 18 h before death increased the accumulation of [3H]‐inositol phosphates ([3H]‐Ins P's) in the brains of mice injected i.c.v. with [3H]‐myo‐inositol 24 h previously.

Pilocarpine (200 mg kg−1, i.p.) injected 15 min before death further enhanced the formation of [3H]‐Ins P's in the brains of LiCl‐treated, but not saline‐treated, mice. The enhancement due to pilocarpine was abolished by injection of atropine sulphate (10 mg kg−1, i.p.) 10 min earlier.

Chronic (14 days) LiCl feeding produced an accumulation of [3H]‐Ins P's significantly less than that due to a single injection of LiCl, but the response to pilocarpine was markedly greater in mice chronically fed with LiCl when compared with mice acutely injected with LiCl.

Mass measurements of endogenous inositol 1,4,5 triphosphate revealed increases due to pilocarpine and chronic LiCl feeding alone. A combination of the two treatments produced levels greater than either alone.

These results demonstrate that LiCl treatment enhances both basal and pilocarpine‐stimulated inositol phospholipid hydrolysis in vivo and this might be relevant to its therapeutic effects.
CI‐977, a novel and selective agonist for the κ‐opioid receptor
Authors: Hunter J.C. , Leighton G.E. , Meecham K.G. , Boyle S.J. , Horwell D.C. , Rees D.C. , Hughes J.
Published: July 2012

CI‐977 is a new, nonpeptide κ‐opioid compound that has been synthesized and its pharmacological properties determined in a series of in vitro and in vivo rodent models.

In radioligand binding studies, with guinea‐pig forebrain homogenates, CI‐977 bound with high affinity to [3H]‐U69593‐labelled κ‐sites (Ki = 0.11 nm) but with low affinity to [3H]‐[d‐Ala2, MePhe4, Glyol5] enkephalin (DAMGO) labelled μ‐sites (Ki = 99nm) and [3H]‐[d‐Pen2,5]enkephalin (DPDPE) labelled δ‐sites (Ki = 1.04 μm). CI‐977 also bound with negligible affinity to [3H]‐(+)‐3‐(1‐propyl‐3‐piperidinyl)phenol (3‐PPP) labelled σ‐sites (Ki = 1.9 μm) and [3H]‐1‐(1‐[2‐thienyl]cyclohexyl)piperidine (TCP) labelled PCP sites (Ki > 10 μm).

CI‐977 produced a potent inhibition of the electrically‐evoked contractions of the guinea‐pig ileum and rabbit vas deferens with IC50 values of 0.087 nM and 3.3 nM, respectively. The pKB values for the opioid antagonists naloxone (7.6) and norbinaltorphimine (10.5) supported the κ nature of the CI‐977‐mediated effects in the smooth muscle assays.

CI‐977 was a potent antinociceptive agent against a mechanical noxious stimulus in rats following intravenous, intramuscular, subcutaneous and oral administration. CI‐977 was also effective against mechanical and chemical noxious stimuli in the mouse but ineffective against a thermal stimulus. The antinociceptive effects produced by CI‐977 were completely reversed by naloxone (1 mg kg−1, s.c.).

At doses close to those required to produce antinociception, CI‐977 also caused a naloxone‐reversible diuresis and inhibition of locomotor activity.

The in vitro and in vivo pharmacological profile of CI‐977 demonstrates that it is a potent and selective agonist at the κ‐opioid receptor.
Kinins and peritoneal exudates induced by carrageenin and zymosan in rats
Authors: Damas Jacques , Bourdon Victor , Remacle‐Volon Gaby , Adam Albert
Published: July 2012

Kinins were measured by a radioimmunoassay in the inflammatory exudates induced by carrageenin or zymosan in the peritoneal cavity of normal Wistar rats and of kininogen‐deficient Brown Norway rats.

After administration of carrageenin to normal rats, levels of immunoreactive kinins showed a single peak during the first two hours and then decreased. The presence of kinins preceded and accompanied the exudation of 125I‐labelled albumin. Kinins were identified as bradykinin by chromatography.

Captopril, an inhibitor of kininase 2, increased the level of kinins and the volume of the exudates after carrageenin treatment. In Brown Norway rats, the volume of the exudates was small and contained little or undetectable amounts of immunoreactive kinins.

During zymosan‐induced peritonitis, the exudates were devoid of immunoreactive kinins in both species. The volume of the exudates was larger in kininogen‐deficient rats than in normal rats.

We conclude that in rats, the kinin system is a major factor responsible for the development of the inflammatory reactions induced by carrageenin, but is not involved in the reactions induced by zymosan.
5‐HT1A agonists increase and 5‐HT3 agonists decrease acetylcholine efflux from the cerebral cortex of freely‐moving guinea‐pigs
Authors: Bianchi Clementina , Siniscalchi Anna , Beani Lorenzo
Published: July 2012

The influence of 5‐hydroxytryptamine1A (5‐HT1A), 5‐HT2 and 5‐HT3 agonists and antagonists on acetylcholine (ACh) release from the cerebral cortex was studied in freely moving guinea‐pigs.

8‐Hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT, 0.01–1 mg kg−1, s.c.) caused the 5‐HT syndrome and dose‐dependently increased ACh release. Ru 24969 (1–10 mg kg−1, s.c.) shared the same effects, but it was less potent. (−)‐Propranolol (5 mg kg−1) and metitepine (2 mg kg−1) prevented these behavioural and neurochemical responses.

(±)‐1(4‐Iodo‐2,5‐dimethoxyphenyl)2‐aminopropane (DOI) up to 2 mg kg−1 did not modify ACh release and ketanserin (0.5 mg kg−1) was ineffective on 5‐HT‐induced changes of ACh outflow.

2‐Methyl‐5‐HT (500 μg, i.c.v.) and 5‐HT (500 μg, i.c.v.) plus metitepine (2 mg kg−1, s.c.) inhibited the gross behaviour and ACh release. ICS 205–930 (0.5 mg kg−1) prevented these responses.

2‐Methyl‐5‐HT, up to 10 μmoll−1, and 8‐OH‐DPAT, up to 0.1 μmoll−1, (like 5‐HT) did not change [3H]‐choline efflux from cerebral cortex slices.

These results suggest that exogenous 5‐HT and related selective agonists modulate guinea‐pig cortical cholinergic structures through 5‐HT1A and 5‐HT3 receptors. The stimulation of 5‐HT1A autoreceptors may lead to disinhibition of the cholinergic cells, tonically inhibited by the tryptaminergic control. Conversely, the stimulation of 5‐HT3 receptors inhibits ACh release, possibly through an interneurone. No direct 5‐HT modulation of the cholinergic nerve endings was found.
Inhibition of nicotine‐induced relaxation of the bovine retractor penis muscle by compounds known to have ganglion‐blocking properties
Authors: Alaranta Sakari , Klinge Erik , Pätsi Tuomo , Sjöstrand Nils O.
Published: July 2012

The relative potency in blocking the nicotine‐induced relaxation of the bovine retractor penis muscle (BRP) was estimated for 12 drugs known to have ganglion‐blocking properties.

The order of potency of the drugs studied was mecamylamine > chlorisondamine > pentolinium > propantheline > (+)‐tubocurarine > hexamethonium > emepronium > tetraethylammonium > glycopyrrolate > decamethonium > butylscopolamine > scopolamine.

The results conform well to those obtained with other pharmacological methods used for the estimation of ganglion‐blocking activity.

It is concluded that blockade of the nicotinic relaxation of the BRP can be used as an alternative method for quantitative assessment of ganglion‐blocking activity.

Advantages of this technique are that it discriminates well between antinicotinic and antimuscarinic activity and that it satisfies most or all ethical and economical demands.

It is also possible that this method has certain value in predicting whether a drug has enough ganglion‐blocking activity to be likely to cause impotence.
The effects of Bay K 8644 and nifedipine on the responses of rat urinary bladder to electrical field stimulation, β,γ‐methylene ATP and acetylcholine
Authors: Bo Xuenong , Burnstock Geoffrey
Published: July 2012

Bay K 8644 (0.33 nm to 1 μm) greatly increased the contractions of rat urinary bladder detrusor muscle induced by β,γ‐methylene ATP (β,γ‐MeATP, 10 μm) and by electrical field stimulation of the purinergic component (the cholinergic response was blocked by atropine).

The contractions induced by acetylcholine (ACh, 10 μm) and by electrical field stimulation of the cholinergic component (the purinergic response was blocked following desensitization by α,β‐MeATP) were also potentiated by Bay K 8644, although to a lesser extent than the purinergic responses.

Nifedipine (1 nm to 3.3 μm) inhibited all the contractions induced by β,γ‐MeATP, ACh and electrical field stimulation. However, while the responses to β,γ‐MeATP and electrical field stimulation of the purinergic component were almost abolished, a substantial proportion of the responses to ACh and electrical field stimulation of the cholinergic component were nifedipine resistant.

The concentration‐effect curves for the potentiation by Bay K 8644 of the responses to β,γ‐MeATP, ACh and electrical field stimulation were shifted to the right by nifedipine (10 nm). At concentrations greater than 1 μm, Bay K 8644 inhibited contraction.

It is concluded that voltage‐sensitive calcium channels play an important role in the excitatory mechanical action of P2x‐purinoceptor‐mediated purinergic responses in the rat urinary bladder, while cholinergic‐mediated responses are less dependent on such channels.
Inability of endothelin to increase Ca2+ current in guinea‐pig heart cells
Authors: Tohse Noritsugu , Hattori Yuichi , Nakaya Haruaki , Endou Masayuki , Kanno Morio
Published: July 2012

Effects of endothelin, a novel vasoconstrictor peptide derived from vascular endothelial cells, on cardiac contractility and membrane currents, were examined in guinea‐pig cardiac preparations. Endothelin (3–1000 nm) produced a positive inotropic effect in papillary muscles in a concentration‐dependent manner. In whole‐cell voltage clamp recording, endothelin (250 nm) decreased the amplitude of Ca2+ current (ICa, 25.0 ± 6.6%) in ventricular myocytes. The endothelin‐induced decrease in ICa was abolished by pretreatment with ryanodine (1 μm). These results suggest that endothelin does not activate cardiac sarcolemmal Ca2+ channels. The enhancement of the sarcoplasmic reticulum function may play an important role in the positive inotropic effect of endothelin.
Role of endothelium and calcium channels in endothelin‐induced contraction of human cerebral arteries
Authors: de Aguilera E. Martín , Irurzun A. , Vila J.M. , Aldasoro M. , Galeote M.S. , Lluch S.
Published: July 2012

Endothelin constricted human isolated cerebral arteries in a concentration‐dependent manner. The maximal tension developed, as well as EC50 values were similar in arteries with and without endothelium. Removal of extracellular calcium or addition of the calcium antagonist nicardipine (10−6 m), attenuated but did not abolish responses to endothelin. These experiments show that the endothelin‐induced contraction in human cerebral arteries is not linked to the presence of intact endothelial cells. The data also show that the contractile effects of endothelin cannot be explained solely by an action on voltage‐dependent calcium channels.
Effects of antiarrhythmic agents classified as class III group on ischaemia‐induced myocardial damage in canine hearts
Authors: Sano T. , Sugiyama S. , Taki K. , Hanaki Y. , Shimada Y. , Ozawa T.
Published: July 2012

The cardioprotective effects of antiarrhythmic agents classified as class III, amiodarone, sotalol and E‐4031, were investigated in anaesthetized dogs.

The left anterior descending coronary artery was occluded for 2 h.

Heart mitochondria were prepared from both the ischaemic and non‐ischaemic areas, and their function was estimated polarographically.

Activities of the lysosmal enzymes, N‐acetyl‐β‐glucosaminidase and β‐glucuronidase, were measured in each fraction.

Two hour occlusion induced ventricular arrhythmias, and amiodarone, sotalol and E‐4031 greatly suppressed the development of arrhythmias.

Amiodarone, sotalol and E‐4031 significantly protected mitochondria against ischaemia, and prevented ischaemia‐induced leakage of lysosomal enzymes.

Antiarrhythmic agents classified as class III show cardioprotective effects, which might participate in their antiarrhythmic effect.
The interaction of parafluorohexahydrosiladiphenidol at muscarinic receptors in vitro
Authors: Eglen R.M. , Michel A.D. , Montgomery W.W. , Kunysz E.A. , Machado C.A. , Whiting R.L.
Published: July 2012

The antagonistic actions of parafluorohexahydrosiladiphenidol (pFHHSiD) at muscarinic receptors has been studied in cardiac muscle, smooth muscle and cell culture preparations. In this paper, the classification scheme of Doods et al. (1987) is employed. This scheme is based upon differential affinities of muscarinic antagonists. pFHHSiD exhibited high pA2 values at M3 receptors mediating contractions of guinea‐pig ileum and oesophageal muscularis mucosae (7.8 and 8.2 respectively) whereas low values were determined at M2 receptors mediating negative inotropic responses in guinea‐pig atria (6.0). Intermediate pA2 values were determined at M1 receptors mediating contractions of the canine femoral and saphenous veins.

The pA2 values of pFHHSiD at receptors mediating endothelial‐dependent relaxation of rat aortic rings, rabbit jugular vein and canine femoral artery (7.6–7.9) were similar to those determined on the ileum. However, the pA2 values of pFHHSiD at receptors mediating contractions of the guinea‐pig trachea (7.1), which has been previously shown to possess M3 receptors, were different from those determined in the ileum.

The similarity in pA2 values of pFHHSiD between the M3 receptors in guinea‐pig ileum and the receptors mediating endothelial‐dependent relaxations provide further evidence for the role of M3 receptors in this vascular response. Taken together, pA2 values for pFHHSiD range from 7.1 to 8.2, depending upon the M3 preparation used. The selectivity of the compound therefore for the M3 versus the M2 muscarinic receptor ranged from 13 to 163 fold.

At muscarinic receptors mediating stimulation of phosphatidylinositol hydrolysis, pFHHSiD paradoxically displayed a high affinity for the M1 receptor in the SH‐SY5Y cell line (pA2 = 7.9) as well as for the M3 receptor in the human astrocytoma (1321 N1 cell line(pA2 = 7.6). The value at the M1 receptor in SH‐SY5Y cells was greater than was observed at M1 receptors mediating contractions of both the canine saphenous and femoral veins (7.1).

pFHHSiD, therefore, clearly delineated M3 from M2 muscarinic receptors, whilst the separation between M1 and M3 receptors was variable. The reason for the anomalous affinity estimates in some functional studies remains unclear. These data indicate that the pA2 values for pFHHSiD appear to be tissue‐dependent since the M3 selectivity varies according to the preparations studied. As a result the utility of pFHHSiD in muscarinic receptor classification is limited.
Differential effect of zinc on the vertebrate GABAA‐receptor complex
Authors: Smart T.G. , Constanti A.
Published: July 2012

γ‐Aminobutyric acid (GABA) responses were recorded from rat superior cervical ganglia (SCG) in culture using the whole cell recording technique.

Zinc (50–300 μm) reversibly antagonized the GABA response in embryonic and young post‐natal neurones, while neurones cultured from adult animals were far less sensitive and occasionally resistant to zinc blockade. Cadmium (100–300 μm) also antagonised the GABA response, while barium (100 μm‐2 mm) was ineffective.

The differential blocking effect of zinc on cultured neurones of different ages also occurred in intact SCG tissue.

The GABA log dose‐response curve constructed with foetal or adult cultured neurones was reduced in a non‐competitive manner by zinc. This inhibition was minimally affected by the membrane potential.

The GABA response recorded intracellularly from guinea‐pig pyriform cortical slices was enhanced by zinc (300–500 μm), which occurred concurrently with a decrease in the input conductance of the cell. The enhancement was unaffected by prior blockade of the GABA uptake carrier by 1 mm nipecotic acid. This phenomenon could be reproduced by barium (300 μm) and cadmium (300 μm).

We conclude that the vertebrate neuronal GABAA‐receptor becomes less sensitive to zinc with neural (GABAA‐receptor?) development, and the enhanced GABA response recorded in the CNS is a consequence of the reduction in the input conductance and not due to a direct effect on the receptor complex.
Adrenergic‐cholinergic interactions in left atria: a study using K + channel agonists, antagonist and pertussis toxin
Authors: Ray Abhijit , MacLeod Kathleen M.
Published: July 2012

The role of activation of potassium conductance in the antagonism by the muscarinic agonist carbachol of positive inotropic responses to α‐ and β‐adrenoceptor stimulation was studied in electrically driven left atrial strips of the rabbit.

The potassium channel antagonist, 4‐aminopyridine, attenuated the direct negative inotropic response to carbachol and the reversal by carbachol of positive inotropic responses to the α‐adrenoceptor agonist phenylephrine (in the presence of timolol). The inhibitory effect of carbachol on positive inotropic responses to the β‐adrenoceptor agonist isoprenaline was much less affected by 4‐aminopyridine.

Pretreatment of rabbits with pertussis toxin also attenuated the direct negative inotropic response to carbachol and the inhibitory effect of carbachol on positive inotropic responses to phenylephrine.

Neither carbachol nor phenylephrine, alone or in combination, had any effect on left atrial adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) levels.

The potassium channel agonist, pinacidil, exerted a dose‐dependent negative inotropic response in rabbit left atria and reversed positive inotropic responses to phenylephrine and isoprenaline. In the dose‐range tested, pinacidil had a greater inhibitory effect on positive inotropic responses to phenylephrine than on positive inotropic responses to isoprenaline.

Pretreatment of left atria with pinacidil or cromakalim, another potassium channel agonist, antagonized positive inotropic responses to phenylephrine but not to isoprenaline.

These results suggest that activation of potassium conductance plays an important role in the inhibition by carbachol of positive inotropic responses of rabbit left atria to phenylephrine but not to isoprenaline.
Release of atrial natriuretic peptide from rat myocardium in vitro: effect of minoxidil‐induced hypertrophy
Authors: Kinnunen Päivi , Taskinen Tarja , Leppäluoto Juhani , Ruskoaho Heikki
Published: July 2012

Ventricular hypertrophy is characterized by stimulation of ventricular synthesis of atrial natriuretic peptide (ANP). To examine the role of ventricular ANP levels in the secretion of ANP into the circulation, atrial and ventricular levels of immunoreactive‐ANP (IR‐ANP) as well as ANP messenger RNA (mRNA), and the release of IR‐ANP from isolated perfused hearts, both before and after atrialectomy, were measured simultaneously in control and minoxidil‐treated Wistar‐Kyoto (WKY) and spontaneously hypertensive (SHR) rats.

IR‐ANP levels in the ventricles of untreated, 12 month‐old SHR with severe ventricular hypertrophy were increased when compared to age‐matched WKY rats. Minoxidil treatment for 8 weeks in both strains resulted in a decrease in mean arterial pressure and increases in ventricular weight to body weight ratios, plasma IR‐ANP concentrations (in WKY from 133 ± 20 to 281 ± 34 pg ml−1, P < 0.01; in SHR from 184 ± 38 to 339 ± 61 pg ml−1, P < 0.05), and in ventricular IR‐ANP contents (in WKY: 53%; in SHR: 41%). A highly significant correlation was found between ventricular IR‐ANP content and ventricular weight to body weight ratio (r = 0.59, P < 0.001, n = 26).

When studied in vitro, in isolated perfused heart preparations, the hypertrophied ventricular tissue after atrialectomy secreted more ANP into the perfusate than ventricles of the control hearts; ventricles contributed 28%, 22%, 18% and 15% of the total ANP release to perfusate in the minoxidil‐treated SHR, control SHR, minoxidil‐treated WKY and control WKY, respectively. A significant correlation was found between the IR‐ANP release from ventricles and ventricular weight to body weight ratio (r = 0.56, P < 0.01, n = 24).

These studies demonstrate that the ventricles contribute substantially to the circulating level of ANP, and that the amount released depends on the degree of ventricular hypertrophy.
Hypotensive effects of 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin and 5‐methylurapidil following stereotaxic microinjection into the ventral medulla of the rat
Authors: Valenta Barbara , Singer Ernst A.
Published: July 2012

The effects of the 5‐HT1a receptor agonists 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) and 5‐methylurapidil (5‐MU) on blood pressure and heart rate were investigated in the anaesthetized normotensive rat after local injection into the ventral medulla (medial part of the area of the B1/B3 cell group).

Both 8‐OH‐DPAT and 5‐MU, decreased arterial blood pressure and heart rate. Local injection of the α1‐adrenoceptor antagonist prazosin did not affect cardiovascular parameters.

Subcutaneous injection of the 5‐HT1a receptor antagonists spiroxatrine or spiperone inhibited the cardiovascular response to 8‐OH‐DPAT and 5‐MU.

Histological examination showed the injection sites which were associated with cardiovascular responses to the agonists to be contained within the medial part of the area of the B1/B3 cell group, corresponding to the region of the nucleus raphe magnus and pallidus. Injections of agonists into adjacent areas had no effect on blood pressure or heart rate.

The results support the hypothesis that activation of somatodendritic 5‐HT1a autoreceptors located on 5‐hydroxytryptaminergic neurones in the ventral medulla of the rat results in a decrease in blood pressure and heart rate. The region of the B1/B3 cell group is suggested as a possible site for the hypotensive action of 5‐HT1a receptor agonists.
Inhibition of neutrophil and eosinophil induced chemotaxis by nedocromil sodium and sodium cromoglycate
Authors: Bruijnzeel P.L.B. , Warringa R.A.J. , Kok P.T.M. , Kreukniet J.
Published: July 2012

Neutrophils and eosinophils infiltrate the airways in association with the allergen‐induced late phase asthmatic reaction. Mobilization of these cells takes place via lipid‐like and protein‐like chemotactic factors. In this study platelet‐activating factor (PAF), leukotriene B4 (LTB4), zymosan‐activated serum (ZAS) and N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) were used as illustrative examples of both groups. Chemotaxis was studied in human neutrophils and eosinophils. The inhibitory effects of nedocromil sodium and sodium cromoglycate were evaluated.

All chemotactic factors tested attracted neutrophils with the following rank order of activity: ZAS > PAF ≡ FMLP ≡ LTB4. Eosinophils were only mobilized by PAF, LTB4 and ZAS with the following rank order of activity: ZAS > PAF > LTB4.

Nedocromil sodium and sodium cromoglycate were equally active as the PAF antagonist BN 52021 in inhibiting the PAF‐induced chemotaxis of neutrophils (IC50 & 10−8 m). Both drugs were also equally active in inhibiting the chemotaxis of neutrophils induced by ZAS (IC50 ≅ 10−7−10−6 m), FMLP(IC50 ≅ 10−7 m) and LTB4 (IC50 ≅ 10−6 m).

Nedocromil sodium significantly inhibited the chemotaxis of eosinophils induced by PAF (IC50 ≅ 10−6 m) and LTB4 (IC50 ≅ 10−7 m). The inhibitory potency of BN 52021 was similar to that of nedocromil sodium on the PAF‐induced chemotaxis of eosinophils. Sodium cromoglycate was incapable of eliciting significant inhibition of these chemotactic responses. However, sodium cromoglycate significantly inhibited the chemotaxis of eosinophils induced by ZAS (IC50 ≅ 10−7 m), whereas nedocromil sodium was ineffective.
Use‐dependent effects of pirmenol on and conduction in guinea‐pig ventricular myocardium
Authors: Hasegawa Junichi , Hirai Shozo , Noguchi Noriyasu , Hisatome Ichiro , Kotake Hiroshi , Mashiba Hiroto
Published: July 2012

The use‐dependent effects of pirmenol, a new antiarrhythmic drug, on the maximal rate of rise of the action potential, conduction velocity, and their corresponding recovery kinetics were studied in isolated papillary muscles of guinea‐pig. Standard microelectrode techniques were used to monitor the conduction and action potential characteristics of the muscles.

Pirmenol decreased and the overshoot of action potentials in a dose‐dependent fashion. Also, doses of pirmenol greater than 1 mm abolished the generation of action potentials. Low concentrations of pirmenol (3 and 10 μm) prolonged the action potential duration, while concentrations greater than 0.1 mm shortened it markedly.

The resting block of in the presence of 10 and 30 μm pirmenol was 9.48 ± 3.12 and 20.36 ± 3.61%, and that of conduction velocity 2.87 ± 1.52 and 6.58 ± 2.09%, respectively.

The degree of use‐dependent block induced by 10 and 30 μm pirmenol during 0.2, 1, 2 and 3 Hz stimulations was dose‐ and rate‐dependent.

In the presence of 30 μm pirmenol, mean values of time constants for the onset of the use‐dependent inhibition of and conduction velocity during a 2 Hz stimulation were 1.32 ± 0.15 and 1.28 ± 0.09 s, respectively. The recovery time constants averaged 15.83 ± 2.14 (for ) and 27.80 ± 8.74 (for conduction velocity) s in the presence of 30 μm pirmenol.

These results showed that the characteristics of the use‐dependent inhibition of and conduction velocity induced by pirmenol are similar to those of slow kinetic drugs such as disopyramide rather than of fast ones.
Behavioural evidence for a functional interaction between central 5‐HT2 and 5‐HT1A receptors
Authors: Backus Lisa I. , Sharp Trevor , Grahame‐Smith David G.
Published: July 2012

The possibility of 5‐HT2 receptor modulation of central 5‐HT1A receptor function has been examined using the 5‐hydroxytryptamine (5‐HT) behavioural syndrome induced by 5‐HT1A receptor active drugs in rats.

The 5‐HT2/5‐HT1C antagonist ritanserin (0.1–2 mg kg−1) increased the 5‐HT behavioural syndrome induced by submaximally effective doses of 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT), 5‐methoxy‐N,N‐dimethyltryptamine (5‐MeODMT) and gepirone.

Pretreatment with the 5‐HT2/5‐HT1C antagonist ICI 170,809 (0.25–5 mg kg−1) also enhanced the behavioural syndrome induced by 8‐OH‐DPAT or 5‐MeODMT.

The 5‐HT2/α1‐adrenoceptor antagonist ketanserin in a low dose (0.25 mg kg−1) significantly increased the 5‐HT behavioural syndrome induced by 8‐OH‐DPAT or 5‐MeODMT, while in a higher dose (2.5 mg kg−1) this drug decreased the response. Experiments with prazosin indicate that the higher dose of ketanserin might reduce the 5‐HT behavioural syndrome through blockade of α1‐adrenoceptors.

Ritanserin and ICI 170,809 had no effect on apomorphine‐induced stereotypy or hyperactivity, indicating that these drugs do not produce non‐specific behavioural activation.

Ritanserin and ICI 170,809 inhibited quipazine‐induced wet dog shakes at doses similar to those enhancing the 5‐HT behavioural syndrome.

We suggest that ritanserin, ICI 170,809 and ketanserin enhance 5‐HT1A agonist‐induced behaviour through blockade of an inhibitory 5‐HT2 receptor regulating or coupled to 5‐HT1A receptor‐mediated function.
Induction of non‐specific airway hyperreactivity by potassium channel blockade in rat isolated trachea
Authors: Chand N. , Diamantis W. , Sofia R.D.
Published: July 2012

The exposure of rat isolated tracheal segment to the K+‐channel inhibitor tetraethylammonium (TEA, 10 mm) for a period of 10–15 min generally produced little or no contractile response.

Cooling (10°C) provocation alone usually produced small (10 ± 3% acetylcholine maximum) contractile responses.

In the presence of TEA (10 mm, 10–15 min exposure), rat trachea exhibited airway hyperreactivity to acetylcholine, 5‐hydroxytryptamine (5‐HT) and cooling. It also increased the peak tension induced by 5‐HT.

TEA‐induced airway hyperreactivity to cooling was signficantly inhibited in Ca2+‐free Krebs solution suggesting an important role for extracellular Ca2+ influx.

We conclude that the blockade of potassium channels with TEA induces non‐specific airway hyperreactivity to cooling, 5‐HT and acetylcholine in rat isolated tracheal segments.
Evidence for the existence of ‘atypical’β‐adrenoceptors (β3‐adrenoceptors) mediating relaxation in the rat distal colon in vitro
Authors: McLaughlin Daniel P. , MacDonald Allan
Published: July 2012

Experiments were carried out to characterize the adrenoceptors mediating relaxant responses in the rat distal colon. Three agonists were used: noradrenaline, isoprenaline and the β3‐adrenoceptor agonist BRL 37344. Phentolamine, propranolol and (±)‐cyanopindolol were tested as antagonists. Tone in the rat distal colon was induced with KCl (30–40 mm) as a spasmogen, and relaxations of this KCl‐induced tone produced by the agonists were measured.

Relaxant responses to noradrenaline that were obtained in the presence of propranolol (1 μm) were not antagonized by phentolamine (0.01 to 1 μm). Relaxant responses to isoprenaline that were obtained in the presence of phentolamine (1 μm) were antagonized in a concentration‐dependent manner by propranolol (0.01 to 3 μm), although this antagonism was weak and non‐competitive. Relaxant responses to BRL 37344 that were obtained in the presence of phentolamine (1 μm) were only weakly antagonized by high (1 μm) concentrations of propranolol.

Tachyphylaxis to BRL 37344 was observed, a second concentration‐response curve being shifted to the right by 15 fold. Exposure of the tissues to BRL 37344 (1 μm) between concentration‐response curves also caused rightward shifts in the responses to noradrenaline (18 fold) and isoprenaline (19 fold) but not to papaverine.

In the presence of phentolamine (1 μm) and propranolol (1 μm), the rank order of potency of the agonists was: (−)‐isoprenaline (1.0) ≥ BRL 37344 (0.93) > (−)‐noradrenaline (0.3).

Responses to BRL 37344 in the presence of phentolamine (1 μm) and propranolol (1 μm) were antagonized by (±)‐cyanopindolol (1 μm), with an apparent pA2 value of 6.67. Responses to isoprenaline, under the same conditions, were antagonized in a competitive manner by (±)‐cyanopindolol (0.1 to 10 μm), with the slope of the Schild plot close to unity and a pA2 value of 7.12.

The resistance of the relaxant responses to antagonism by phentolamine and propranolol, along with the relatively high potency of the β3‐adrenoceptor agonist BRL 37344 and the antagonism of ‘resistant’ responses by (±)‐cyanopindolol would suggest that ‘atypical’ β‐adrenoceptors, similar to the β3‐adrenoceptors of rat adipocytes and other tissues, exist in the rat distal colon.