bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of κ‐opioid receptor stimulation in the heart and the involvement of protein kinase C
Authors: Bian Jin‐Song , Wang Hong‐Xin , Zhang Wei‐Min , Wong Tak‐Ming 
Published: January 2005

The role of protein kinase C (PKC) in mediating the action of κ‐receptor stimulation on intracellular Ca2+ and cyclic AMP production was determined by studying the effects of trans‐(±)‐3,4‐dichloro‐N‐methyl‐N‐(2‐[1‐pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate (U50,488H), a selective κ‐receptor agonist, and phorbol 12‐myristate 13‐acetate (PMA), a PKC agonist, on the electrically‐induced [Ca2+]i transient and forskolin‐stimulated cyclic AMP accumulation in the presence and absence of a PKC antagonist, staurosporine or chelerythrine, in the single rat ventricular myocyte.
U50,488H at 2.5–40 μM decreased both the electrically‐induced [Ca2+]i transient and forskolin‐stimulated cyclic AMP accumulation dose‐dependently, effects which PMA mimicked. The effects of the κ‐agonist, that were blocked by a selective κ‐antagonist, nor‐binaltorphimine, were significantly antagonized by the PKC antagonists, staurosporine and/or chelerythrine. The results indicate that PKC mediates the actions of κ‐receptor stimulation.
To determine whether the action of PKC was at the sarcoplasmic reticulum (SR) or not, the [Ca2+]i transient induced by caffeine, that depletes the SR of Ca2+, was used as an indicator of Ca2+ content in the SR. The caffeine‐induced [Ca2+]i transient was significantly reduced by U50,488H at 20 μM. This effect of U50,488H on caffeine‐induced [Ca2+]i transient was significantly attenuated by 1 μM chelerythrine, indicating that the action of PKC involves mobilization of Ca2+ from the SR. When the increase in IP3 production in response to κ‐receptor stimulation with U50,488H in the ventricular myocyte was determined, the effect of U50,488H was the same in the presence and absence of staurosporine, suggesting that the effect of PKC activation subsequent to κ‐receptor stimulation does not involve IP3. The observations suggest that PKC may act directly at the SR.
In conclusion, the present study has provided evidence for the first time that PKC may be involved in the action of κ‐receptor stimulation on Ca2+ in the SR and cyclic AMP production, both of which play an essential role in Ca2+ homeostasis in the heart.
Role of hyperthermia in the protective action of clomethiazole against MDMA (‘ecstasy’)‐induced neurodegeneration, comparison with the novel NMDA channel blocker AR‐R15896AR
Authors: Colado M I , Granados R , O'Shea E , Esteban B , Green A R 
Published: January 2005

The immediate effect of administration of 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) on rectal temperature and the effect of putative neuroprotective agents on this change has been examined in rats. The influence of the temperature changes on the long term MDMA‐induced neurodegeneration of cerebral 5‐hydroxytryptamine (5‐HT) nerve terminals was also examined.
The novel low affinity N‐methyl‐D‐aspartate (NMDA) receptor channel blocker AR‐R15896AR (20 mg kg−1, i.p.) given 5 min before and 55 min after MDMA (15 mg kg−1, i.p.) did not prevent the MDMA‐induced hyperthermia and did not alter either the MDMA‐induced neurodegenerative loss of 5‐HT and 5‐hydroxyindoleacetic acid (5‐HIAA) in cortex, striatum and hippocampus or loss of [3H]‐paroxetine binding in cortex 7 days later.
The neuroprotective agent clomethiazole (50 mg kg−1, i.p.) given 5 min before and 55 min after MDMA (15 mg kg−1) abolished the MDMA‐induced hyperthermic response and markedly attenuated the loss of 5‐HT, 5‐HIAA and [3H]‐paroxetine binding in the brain regions examined 7 days later.
When rats treated with MDMA plus clomethiazole were kept at high ambient temperature for 5 h post‐MDMA, thereby keeping their body temperature elevated to near that seen in rats given MDMA alone, the MDMA‐induced loss of 5‐HT, 5‐HIAA and [3H]‐paroxetine was still attenuated. However, the protection (39%) afforded by the clomethiazole administration was less than seen in rats kept at normal ambient temperature (75%).
These data support the proposals of others that NMDA receptor antagonists are neuroprotective against MDMA‐induced degeneration only if they induce hypothermia and further suggest that increased glutamate activity may not be involved in the neurotoxic action of MDMA.
These data further demonstrate that a proportion of the neuroprotective action of clomethiazole is due to an effect on body temperature but that, in addition, the compound protects against MDMA‐induced damage by an unrelated mechanism.
T‐type and L‐type calcium channel blockers exert opposite effects on renin secretion and renin gene expression in conscious rats
Authors: Wagner Charlotte , Krämer Bernhard K , Hinder Markus , Kieninger Martin , Kurtz Armin 
Published: January 2005

This study aimed to investigate and to compare the effects of pharmacological T‐type calcium channel and of L‐type calcium channel blockade on the renin system. To this end, male healthy Sprague‐Dawley rats were treated with the T‐channel blocker mibefradil or with the L‐channel blocker amlodipine at doses of 5 mg kg−1, 15 mg kg−1 and 45 mg kg−1 per day for four days and their effects on plasma renin activity (PRA) and kidney renin mRNA levels were determined.
Whilst amlodipine lowered basal systolic blood pressure at 5 mg kg−1, mibefradil had no effect on basal blood pressure in the whole dose range examined. Amlodipine dose‐dependently induced up to 7 fold elevation of PRA and renin mRNA levels. Mibefradil significantly lowered PRA and renin mRNA levels at 5 mg kg−1 and moderately increased both parameters at a dose of 45 mg kg−1, when PRA and renin mRNA levels were increased by 100% and 30%, respectively. In primary cultures of renal juxtaglomerular cells neither amlodipine nor mibefradil (0.1–10 μM) changed renin secretion.
In rats unilateral renal artery clips (2K‐1C) mibefradil and amlodipine at doses of 15 mg kg−1 day−1 were equally effective in lowering blood pressure. In contrast mibefradil (5 mg kg−1 and 15 mg kg−1 day−1) significantly attenuated the rise of PRA and renin mRNA levels, whilst amlodipine (15 mg kg−1) additionally elevated the rise of PRA and renin mRNA levels in response to renal artery clipping.
These findings suggest that T‐type calcium channel blockers can inhibit renin secretion and renin gene expression in vivo, whilst L‐type calcium channel blockers act as stimulators of the renin system. Since the inhibitory effect of T‐type antagonists is apparent in vivo but not in vitro, one may infer that the effect on the renin system is indirect rather than directly mediated at the level of renal juxtaglomerular cells.
Differential regulation of β3‐adrenoceptors in gut and adipose tissue of genetically obese (ob/ob) C57BL/6J‐mice
Authors: Evans Bronwyn A , Papaioannou Maria , Anastasopoulos Frank , Summers Roger J 
Published: January 2005

Levels of β3‐adrenoceptor (AR) mRNA were compared using reverse transcription‐polymerase chain reaction (RT–PCR) in white adipose tissue (WAT), brown adipose tissue (BAT), ileum and colon from genetically obese (ob/ob) and lean (+/+) C57BL/6J mice. Functional responses to the β3‐AR agonist CL 316243 were also characterized in ileal longitudinal smooth muscle from obese and lean mice.
β3‐AR mRNA levels were significantly higher in WAT (100±16%) and BAT (100±13%) from lean compared to WAT (21.0±0.9%; n=4; P<0.005) and BAT (14.1±2.2%; n=5; P<0.01) from obese mice. In contrast, β3‐mRNA levels were not significantly different in ileum (100±15%) and colon (100±22%) from lean mice, compared to ileum (78±13%; n=4; P=0.31) or colon (82±15%; n=4; P=0.52) from obese mice.
Concentration‐response curves to CL 316243 did not differ significantly in slope or position in ileal longitudinal smooth muscle from obese or lean mice. pEC50 (±s.e.mean) values were not significantly different (P=0.59) between obese (7.90±0.13, n=7) and lean (7.77±0.20, n=7) mice.
pKB values for the β1‐AR and β2‐AR selective antagonist propranolol or the β3‐AR selective antagonist SR 58894 against relaxations to CL 316243 were similar in ileum of genetically obese (propranolol 6.31±0.22 and 6.13±0.12; SR 58894 8.22±0.06) and lean mice (propranolol 6.40±0.08 and 6.60±0.13; SR 58894 8.27±0.12) and were consistent with values previously found at β3‐AR.
Treatment of lean C57BL/6J mice with dexamethasone (1 mg kg−1, i.p.) significantly reduced β3‐AR mRNA levels after 4 h in WAT (100±6.1 to 41.4±4.3; n=16–18; P<0.0001) and BAT (100±8.0 to 35.1±5.8; n=17; P<0.0001), but caused no change in ileum (100±6.1 to 101±17; n=10–11; P=0.95) or colon (100±11 to 101±11; n=11; P=0.94). β3‐mRNA levels in ileum and colon also did not change significantly when examined over 24 h or after the administration of a higher dose of dexamethasone (5 mg kg−1).
In summary, β3‐AR mRNA levels were considerably lower in WAT and BAT of obese compared to lean mice whereas the levels in ileum and colon were not significantly different. The similar β3‐mRNA levels in ileum of obese and lean mice were associated with indistinguishable responses of carbachol‐contracted ileum to a β3‐agonist and similar affinity for β‐antagonists. Administration of glucocorticoids to lean mice reduced β3‐AR mRNA levels in WAT and BAT but not in ileum or colon. These studies show that in mice, β3‐ARs are differentially regulated in ileum and colon compared to adipose tissues.
Selectivity of action of 8‐alkylamino analogues of N6‐cyclopentyladenosine in vivo: haemodynamic versus anti‐lipolytic responses in rats
Authors: Van Schaick E A , Tukker H E , Roelen H C P F , IJzerman A P , Danhof M 
Published: January 2005

A1 adenosine receptor agonists with reduced intrinsic activity may be therapeutically useful as result of an increased selectivity of action. In this study the tissue selectivity of three 8‐alkylamino substituted analogues of N6‐cyclopentyladenosine (CPA) was investigated for haemodynamic and anti‐lipolytic effects using an integrated pharmacokinetic‐pharmacodynamic approach.
Chronically instrumented male Wistar rats received intravenous infusions of 4.0 mg kg−1 8‐methylaminoCPA (8MCPA), 12.0 mg kg−1 8‐ethylaminoCPA (8ECPA), 20.0 mg kg−1 8‐butylaminoCPA (8BCPA) or vehicle during 15 min. During experimentation, serial arterial blood samples were drawn for the determination of agonist concentrations and plasma non‐esterified fatty acid (NEFA) levels. Blood pressure and heart rate were monitored continuously. In addition to the CPA analogues, each rat received a rapid bolus infusion of CPA to determine the maximal effects of the full agonist.
The concentration‐time profiles of the CPA analogues could be described by a bi‐exponential function. Values for clearance, volume of distribution at steady state and elimination half‐life were 44±5, 48±6 and 39±2 ml min−1 kg−1, 0.97±0.09, 0.84±0.10 and 1.05±0.07 1 kg−1 and 25±2, 28±2 and 40±2 min for 8MCPA, 8ECPA and 8BCPA, respectively (mean±s.e.mean, n=6–8).
Different models were used to derive the concentration‐effect relationships for heart rate and NEFA, yielding estimates of potency (EC50) and instrinsic activity (Emax) for both effects of the compounds in vivo. On heart rate the compounds acted as partial agonists, with Emax values of −173±14, −131±11 and −71±6 beats min−1 for 8MCPA, 8ECPA and 8BCPA, respectively. These Emax values were significantly lower than the maximal effect of CPA (−208±8 beats min−1). With regard to the anti‐lipolytic effect all three compounds were full agonists and lowered NEFA levels to the same extent as CPA (69%). The estimated Emax values were 63±5, 63±4 and 68±2%, respectively.
Furthermore, the compounds were more potent in causing anti‐lipolytic than cardiovascular effects. The EC50 values for the NEFA and heart rate lowering effects were 37±15, 68±22 and 659±108 ng ml−1 and 164±22, 341±76 and 975±190 ng ml−1 for 8MCPA, 8ECPA and 8BCPA, respectively (mean±s.e.mean, n=6–8).
This study demonstrates that partial agonists for the A1 adenosine receptor have increased selectivity of action in vivo. The 8‐alkylamino analogues of CPA may be useful anti‐lipolytics with less pronounced haemodynamic side effects.
Depression of NMDA receptor‐mediated synaptic transmission by four α2 adrenoceptor agonists on the in vitro rat spinal cord preparation
Authors: Faber E S L , Chambers J P , Evans R H 
Published: January 2005

α2‐Adrenoceptor agonists have a spinal site of analgesic action. In the current study the synaptic depressant actions of xylazine, detomidine, romifidine and dexmedetomidine have been compared on segmental reflexes containing NMDA receptor‐mediated components in the neonatal rat hemisected spinal cord preparation in vitro.
Reflexes were evoked in the ventral root following either supramaximal electrical stimulation of the corresponding ipsilateral lumbar dorsal root to evoke the high intensity excitatory postsynaptic potential (e.p.s.p.) involving all primary afferent fibres, or low intensity stimulation to evoke the solely A fibre‐mediated low intensity e.p.s.p. The high intensity e.p.s.p. contains a greater NMDA receptor‐mediated component.
Xylazine, romifidine, detomidine and dexmedetomidine all depressed both the high intensity e.p.s.p. and the low intensity e.p.s.p. giving respective EC50 values of 0.91±0.2 μM (n=12), 23.4±3 nM (n=12), 37.7±7 nM (n=8) and 0.84±0.1 nM (n=4) for depression of the high intensity e.p.s.p. and 0.76±0.1 μM (n=12), 22.0±3 nM (n=12), 24.9±6 nM (n=4) and 2.7±0.6 nM (n=4) for depression of the low intensity e.p.s.p., respectively. Unlike the other three drugs, the two values for dexmedetomidine, showing a greater selectivity for the high intensity e.p.s.p., are significantly different.
Each of these depressant actions was reversed by the selective α2‐adrenoceptor antagonist atipamezole (1 μM).
In contrast to previous reports of the actions of α2‐adrenoceptor agonists on the in vitro spinal cord preparation, at concentrations ten fold higher than the above EC50 values xylazine, romifidine, detomidine and dexmedetomidine depressed the initial population spike of motoneurons (MSR). This depression was not reversed by atipamezole.
Comparison of the rank order of the present EC50 values for depression of the high intensity e.p.s.p. with potency ratios from in vivo analgesic tests in previous studies show a close correlation between the present in vitro tests and analgesic potency. There is no correlation between the present data and previously obtained affinities of the agonists at non‐adrenergic imidazoline binding sites.
The current findings therefore suggest that xylazine, romifidine, detomidine and dexmedetomidine are exerting their central analgesic actions at the spinal level principally through α‐2‐adrenoceptors. All four agonists showed the same profile of selective depression of the NMDA receptor‐mediated component of reflexes similar to that reported previously for clonidine. However dexmedetomidine, unlike the other ligands, selectively depressed the high intensity e.p.s.p.
Impairment in connective tissue mast cells degranulation in spontaneously hypertensive rats: stimulus dependent resistance
Authors: Kwasniewski F H , Tavares de Lima W , Bakhle Y S , Jancar S 
Published: January 2005

Microvascular permeability in the mesentery and consequent leakage of protein into the peritoneum of spontaneously hypertensive rats (SHR) and normotensive rats (NTR) was measured in vivo by the extravasation of Evans blue dye.
In sensitized NTR, challenge with antigen produced extensive increases in dye extravasation in the mesentery and in peritoneal lavage fluid within 10 min.
In sensitized SHR there was no increase in the permeability of the mesentery and a very weak increase in dye extravasation in the peritoneal cavity following challenge.
The glucocorticoid antagonist RU38486 did not change the permeability response induced by antigen in sensitized NTR and SHR.
However, compound 48/80 was equally effective in either NTR or SHR in causing increased vasopermeability.
Mesenteric mast cells in the NTR were degranulated after immunological challenge, whereas those in the SHR were resistant, as measured histologically.
Similarly, challenge ex vivo of mesentery from sensitized NTR induced contraction of guinea‐pig ileum in co‐incubation experiments, whereas SHR mesentery was unresponsive.
Plasma levels of antigen‐specific IgE and IgG2a in sensitized NTR and SHR were identical.
Immune serum from SHR was unable to induce a passive cutaneous anaphylaxis (PCA) reaction in the skin of NTR and SHR did not develop a PCA reaction upon passive sensitization with NTR immune serum.
We conclude that the mast cells of SHR are resistant to degranulation following immunological challenge, although the relevant antibodies are present.
The effects of propofol on macroscopic and single channel sodium currents in rat ventricular myocytes
Authors: Saint David A 
Published: January 2005

The effects of the injectable anaesthetic agent propofol (di‐isopropyl phenol) were examined on sodium currents and single sodium channels by use of patch‐clamp techniques in ventricular myocytes isolated from rat hearts.
Propofol dose‐dependently blocked the whole cell sodium currents evoked by a voltage step to −30 mV from a holding potential of −90 mV with an EC50 of 14.8±2.3 μM (mean±s.e.mean).
Propofol caused a substantial hyperpolarizing shift in the voltage‐dependence of inactivation of sodium currents (168 μM (30 μg ml−1) propofol caused a −14 mV shift (P<0.01); 56 μM caused a −8 mV shift (P<0.05)). A smaller shift in the voltage‐dependence of activation was produced (4 mV by 168 μM (not statistically significant)), but this was to more depolarized potentials. The maximal sodium conductance, as judged from the activation and inactivation curves, was reduced by 13% by 168 μM propofol (not statistically significant), but propofol did not affect the reversal potential of the current ‐ voltage relationship.
The macroscopic rate of inactivation, as measured by the time constant of the exponential fall of current amplitude from the peak current, was also slowed by propofol, from a control time constant of 1.78±0.31 ms to 2.93±0.47 ms (mean±s.e.mean, n=8, P<0.05) by 168 μM propofol. Despite the increase in the time constant, the macroscopic inactivation remained well fitted by a single exponential. The macroscopic rate of activation was also slowed, but to a lesser degree (<10%, not statistically significant) by 168 μM propofol.
Propofol slowed the rate of recovery from inactivation of the sodium current, as measured by a two pulse protocol. Propofol (168 μM) increased the time constant of recovery, measured at −100 mV and room temperature, from a control value of 55±5.9 ms to 141±24.2 ms (mean±s.e.mean, n=8, P<0.01). Although the time constant was increased at all voltages measured, the intrinsic voltage‐dependence of the rate of recovery was not changed.
Single channel recordings showed that the mean open time of single sodium channels was dramatically reduced by propofol (from 0.50±0.02 ms in control to 0.28±0.01 ms by 56 μM propofol and to 0.24±0.01 ms by 168 μM, both significantly different from control, P<0.01). Single channel conductance was not changed by either concentration of propofol.
Effects of cetirizine on the delayed K+ currents in cardiac cells: comparison with terfenadine
Authors: Carmeliet Edward 
Published: January 2005

The aim of the present experiments was to analyse the effect of the H1‐histamine antagonist, cetirizine, on the delayed K+ currents in cardiac cells and to compare its effects with another H1‐histamine antagonist terfenadine, known to possess proarrhythmic effects.
Whole cell currents were measured by use of the single electrode patch‐clamp technique in rabbit and guinea‐pig myocytes.
The activation relationship for the IKr current in rabbit ventricular myocytes was depressed and its voltage‐dependence shifted in the negative direction with a V1/2 value −13.4±2.4 mV under control conditions which changed to −19.1±1.9 mV (n=4) in the presence of 0.1 mM cetirizine.
In rabbit ventricular myocytes the IC50 for block of IKr was 108±8 μM (n=5); in guinea‐pig ventricular myocytes this concentration of cetirizine reduced the rapidly activating component IKr to 49±4.5% (n=5), while the slowly activating IKs was less affected and only inhibited to 79±2.3% (n=5).
The block of IKr did not show use‐dependence and the time course of the tail current was not changed, suggesting rested‐state block or fast activated‐state block and no rapid recovery on deactivation. No important difference was found in the activity of the two enantiomers of cetirizine.
Terfenadine in comparison was more potent in blocking IKr, the IC50 being 96±15 nM (n=6).
Based on the present results and information in the literature on binding, it was concluded that cetirizine is a relatively selective H1‐histamine receptor antagonist, with minor effects on K+ currents. The IC50 concentration for IKr block in heart cells was 1.000 times higher than the concentrations needed to block H1 histamine receptors. The occurrence of cardiac arrhythmias due to K+ current blockade is therefore unlikely with this drug.
ATP and adenosine inhibit transmitter release at the frog neuromuscular junction through distinct presynaptic receptors
Authors: Giniatullin R A , Sokolova E M 
Published: January 2005

The effects of exogenous ATP or adenosine on end‐plate currents (e.p.cs; evoked by simultaneous action of a few hundred quanta of ACh) or on miniature e.p.cs (m.e.p.cs) were studied under voltage clamp conditions on frog sartorius muscle fibres.
ATP or adenosine (100 μM–1 mM) reduced the e.p.c. amplitude but did not affect m.e.p.c. amplitude, decay time constant and voltage‐dependence of m.e.p.c., suggesting that e.p.c. depression induced by these purines had presynaptic origin only.
The action of ATP, unlike that of adenosine, was prevented by the P2‐purinoceptor antagonist suramin (100 μM). The stable ATP analogue α,β‐methylene ATP (100 μM), known to be desensitizing agent on P2X receptors, also abolished the depressant effect of ATP while sparing the action of adenosine. Concanavalin A, an inhibitor of ecto‐5′‐nucleotidase, did not affect the presynaptic action of exogenously applied ATP.
The presynaptic action of adenosine was prevented by theophylline (1 mM), a blocker of adenosine receptors, while the effect of ATP was not changed under these conditions. The selective blocker of A1 adenosine receptors, 8‐cyclopentyl‐1,3,dipropylxanthine (DPCPX; 0.1 μM), abolished the presynaptic action of adenosine but did not prevent the depressant effect of ATP.
The effects of ATP and adenosine (at nearly saturating concentration) were additive suggesting that these purines activated not only distinct receptors but also different intracellular signalling mechanisms.
In contrast to the hypothesis that at the neuromuscular junction ATP reduces transmitter release via enzymatic degradation to presynaptically active adenosine, our data suggest that ATP (through its own presynaptic receptors) directly inhibits ACh release. Thus, ATP and adenosine might be almost equipotent as endogenous prejunctional neuromodulators at the neuromuscular junction.