bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Reversals of the neostigmine‐induced tetanic fade and endplate potential run‐down with respect to the autoregulation of transmitter release
Authors: Chang C.C. , Chen S.M. , Hong S.J. 
Published: July 2012

In order to shed more light on the role of presynaptic cholinoceptors in the modulation of transmitter release, the effects of tubocurarine, choline and hexamethonium on neostigmine‐induced tetanic fade and run‐down of endplate potentials (e.p.ps) in response to indirect stimulation with trains of pulses were studied in the intact and cut isolated phrenic nerve‐diaphragm preparation of the mouse, respectively.
Tubocurarine, choline and hexamethonium reduced both the tetanic fade and e.p.p. run‐down caused by neostigmine, despite the fact that they themselves also induced these two effects.
At a given degree of postsynaptic inhibition, choline and hexamethonium caused less e.p.p. run‐down and reversed the neostigmine‐induced tetanic fade and e.p.p. run‐down better than tubocurarine. Moreover, the e.p.p. run‐down caused by choline or hexamethonium, but not that induced by tubocurarine, was reciprocally reversed by neostigmine.
Tubocurarine, choline and hexamethonium significantly decreased the endplate depolarization induced by repetitive nerve stimulation in the presence of neostigmine. The remaining depolarization continued to grow during repetitive stimulation in the presence of choline or hexamethonium, but not, however, in the presence of tubocurarine; a finding which suggests that choline and hexamethonium but not tubocurarine may be displaced from the receptor by the accumulated acetylcholine.
The mutual reversal by neostigmine and cholinoceptor antagonists of e.p.p. run‐down may implicate the presence of a positive (physiological) and a negative (pharmacological) feedback regulation for evoked transmitter release via nicotinic cholinoceptors in the mammalian motor nerve, depending on the concentration of acetylcholine within the synaptic cleft.
Effect of the ‘antidementia drug’ pantoyl‐GABA on high affinity transport of choline and on the contents of choline and acetylcholine in rat brain
Authors: Nakahiro Masanobu , Mochizuki Daisuke , Uchida Shuji , Yoshida Hiroshi 
Published: July 2012

Effect of pantoyl‐γ‐aminobutyric acid (pantoyl‐GABA) on high affinity transport of choline into synaptosomes and on the choline (Ch) and acetylcholine (ACh) concentrations of rat brain were studied.
Pantoyl‐GABA was injected intraperitoneally four times at a dose of 500mgkg−1 at intervals of 30min. One hour after the last injection, rats were killed by decapitation for measurement of high affinity transport of Ch into synaptosomes or by microwave irradiation for the measurement of Ch and ACh concentrations.
Transport of Ch was increased into synaptosomes prepared from the cerebral cortex and hippocampus, but not into those from the striatum.
In the cerebral cortex and hippocampus, Ch concentration was increased and ACh concentration decreased.
Since treatments that enhance the activity of cholinergic neurones in vivo are reported to increase high affinity transport of Ch measured in vitro, the present results suggest that pantoyl‐GABA may increase cholinergic activity in vivo. This action of the drug may be related to changes in the Ch and ACh concentrations.
Platelet inhibition by endothelium‐derived relaxing factor from the rabbit perfused aorta
Authors: Bult Hidde , Fret Hermine R.L. , Van den Bossche Rita M. , Herman Arnold G. 
Published: July 2012

The platelet inhibiting activity of endothelium‐derived relaxing factor (EDRF) released by the perfused thoracic aorta of the rabbit was investigated.
The aortic effluent superfused a ring of the abdominal aorta without endothelium in order to bioassay EDRF. Aliquots of effluent were collected on rabbit washed platelets and aggregation induced by U‐46619 was measured after 1 min. Prostacyclin (PGI2) was monitored by radioimmunoassay of 6‐oxo‐prostaglandin F1α.
Acetylcholine (ACh) caused a dose‐dependent secretion of EDRF, PGI2 and anti‐aggregating activity. Plasma and methylene blue suppressed the platelet inhibition by the effluent.
The PGI2 content of the effluent was not sufficient to account for all the anti‐aggregating activity. However, the platelet inhibition disappeared when PGI2 formation was blocked with indo‐methacin.
Compression of the thoracic aorta increased the EDRF content in the effluent. A transient secretion of anti‐aggregating activity was then observed in aortic effluent in the absence of PGI2. This activity coincided with the presumed EDRF peak in the effluent.
Superoxide dismutase enhanced the ACh‐induced EDRF content and revealed secretion of an anti‐aggregating substance when PGI2 formation was blocked. Pretreatment of the platelets with subthreshold concentrations of PGI2, or the cyclic GMP phosphodiesterase inhibitor RX‐RE 56, also revealed the release of a labile platelet inhibitor in response to ACh.
The results indicate that EDRF released by fresh aortic endothelium may suppress platelet aggregation, particularly when PGI2 is present.