bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contrasting effects of the imidazol(in)e α2‐adrenoceptor agonists, medetomidine, clonidine and UK 14,304 on extraneuronal levels of noradrenaline in the rat frontalcortex: evaluation using in vivo microdialysis and synaptosomal uptake studies
Authors: Dalley J.W. , Stanford S.C. 
Published: July 2012

In vivo microdialysis in halothane‐anaesthetized rats and synaptosomal [3H]‐noradrenaline uptake studies in vitro were used to evaluate the effects of imidazole (medetomidine) and imidazoline (clonidine and UK 14,304) α2‐adrenoceptor agonists on extraneuronal levels of noradrenaline in the frontal cortex.
Levels of noradrenaline in the dialysate were increased by a depolarizing concentration of K+ (60 mM for 20 min) and substantially attenuated by reducing Ca2+ supply in the perfusate. These results suggest that spontaneous efflux of noradrenaline in the cortex is regulated predominantly by cation‐dependent exocytotic mechanisms.
At a low perfusion concentration (0.5 μm), medetomidine, clonidine and UK 14,304 all reduced the level of noradrenaline in cortical dialysates. Continuous perfusion of the selective α2‐adrenoceptor antagonist, atipamezole (0.5 μm) caused a sustained increase in noradrenaline efflux and reversed the inhibitory effects of medetomidine. All these changes are consistent with drug actions at presynaptic α2‐adrenoceptors.
Higher concentrations of medetomidine (5–50 μm), but not clonidine or UK 14,304, evoked a non‐desensitizing increase in noradrenaline efflux. This effect was not antagonized by 0.5 μm atipamezole.
The tricyclic noradrenaline reuptake inhibitor, desmethylimipramine (0.5–50 μm), increased noradrenaline efflux in a concentration‐dependent manner.
The specific uptake of [3H]‐noradrenaline into cortical synaptosomes was inhibited by medetomidine and desmethylimipramine with IC50 values of approximately 7μm and 8mUm respectively. Neither clonidine nor UK 14,304 inhibited [3H]‐noradrenaline uptake.
These results indicate that micromolar concentrations of the selective α2‐adrenoceptor agonist, medetomidine, can augment extraneuronal levels of noradrenaline in the rat frontal cortex; this effect seems to involve an inhibition of noradrenaline reuptake rather than an action at α2‐adrenoceptors.
Actions of the novel neuroprotective agent, lifarizine (RS‐87476), on voltage‐dependent sodium currents in the neuroblastoma cell line, N1E‐115
Authors: McGivern Joseph G. , Patmore Leslie , Sheridan Robert D. 
Published: July 2012

The actions of the neuroprotective agent, lifarizine (RS‐87476‐190), on voltage‐dependent Na+ currents have been examined in the neuroblastoma cell line, N1E‐115, using the whole‐cell variant of the patch clamp technique.
At a holding potential of −80 mV, lifarizine reduced the peak Na+ current evoked by a 10 ms depolarizing step with an IC50 of 1.3μm. At holding potentials of −100 and −60mV the IC50 concentrations of lifarizine were 7.3 μm and 0.3μm, respectively.
At a holding potential of −100 mV, most channels were in the resting state and the IC50 value for inhibition of Na+ current should correspond to the dissociation constant of lifarizine for resting channels (KR). Kr was therefore estimated to be 7.3 μm.
In the absence of lifarizine, recovery from inactivation following a 20 s depolarization from −100 mV to 0 mV was complete within 2 s. However, in the presence of 3 μm lifarizine recovery took place in a biexponential fashion with time constants of 7 s and 79 s.
Lifarizine (1 μm) had no effect on steady‐state inactivation curves when conditioning pre‐pulses of 1 s duration were used. However, when pre‐pulse durations of 1 min were used the curves were shifted to the left by lifarizine by about 10 mV. Analysis of the shifts induced by a range of lifarizine concentrations revealed that the apparent affinity of lifarizine for the inactivated state of the channel (KI) was 0.19 μm.
Lifarizine (1 μm) had no effect on chloramine‐T‐modified Na+ currents, suggesting no significant open channel interaction.
Taken together, these data show that lifarizine is a potent voltage‐dependent inhibitor of Na+ currents in N1E‐115 cells and that the voltage‐dependence arises from an interaction of the compound with the inactivated state of the channel. The possible contribution of Na+ current inhibition to the neuroprotective actions of lifarizine is discussed.
Electrocardiographic interactions between pinacidil, a potassium channel opener and class I antiarrhythmic agents in guinea‐pig isolated perfused heart
Authors: Yang Quan , Padrini Roberto , Bova Sergio , Piovan Donatella , Magnolfi Gianna 
Published: July 2012

Drugs that shorten action potential duration could decrease the Na‐channel blocking effect of class I antiarrhythmic agents by reducing the availability of Na channel in the inactivated state.
This hypothesis was tested in guinea‐pig perfused heart, measuring the surface ECG effects of three class I drugs endowed with different binding kinetics (15 μm mexiletine, 10 μm quinidine and 3 μm flecainide) in the presence of increasing concentrations of pinacidil (10 μm, 30 μm, 50 μm), a potassium channel opener that shortens action potential duration.
The ECG parameters measured were: the QRS interval, i.e. the intraventricular conduction time; the JT interval, which reflects the duration of ventricular repolarization; the ratio between JTpeak (the time from the end of QRS and the peak of T wave) and JT interval, which quantifies changes in the morphology of the T wave.
At the concentrations tested all the antiarrhythmic drugs widened the QRS complex by 55–60%. Flecainide did not significantly change JT interval, but quinidine prolonged and mexiletine shortened it. Mexiletine also decreased the JTpeak/JT ratio. Pinacidil by itself decreased the JT interval and the JT peak/JT ratio in a dose‐dependent way, but did not affect QRS duration.
In the presence of fixed antiarrhythmic drug concentrations, however, pinacidil decreased the QRS prolongation induced by mexiletine (−17%) and quinidine (− 8%), but not that induced by flecainide: this effect was already maximal at the lower concentration tested (10 μm) and there was no relationship between pinacidil‐induced JT shortening and QRS changes. To explain this unexpected result it has been supposed that, at the driving frequency used (4 Hz), myocardial cells were partially depolarized and that pinacidil could repolarize them, thus decreasing the number of inactivated Na channels and the effects of drugs that (mainly or partly) block the channels in the inactivated state. In agreement with this hypothesis, an additional series of experiments carried out with 15 μm mexiletine at a lower stimulation rate (2 Hz) showed only a negligible loss of QRS effect (−2.3%) at any pinacidil concentration.
Flecainide, but not quinidine and mexiletine, antagonized the JT shortening induced by pinacidil; furthermore, no drug modified the JTp/JT decrease induced by pinacidil.
These results indicate that: (a) an antagonism between class I antiarrhythmic drugs and pinacidil is possible; (b) mexiletine is the most involved among the drugs tested; (c) the interaction is not related to pinacidil‐induced repolarization shortening, but probably to changes in membrane resting potential. The possible clinical implications need to be defined.
Additive effect of ADP and CGRP in modulation of the acetylcholine receptor channel in Xenopus embryonic myocytes
Authors: Liou Jau‐Cheng , Fu Wen‐Mei 
Published: July 2012

We have previously shown that the activation of either protein kinase A (PKA) or protein kinase C (PKC) enhanced the responses of muscle membrane to acetylcholine (ACh) by increasing the mean open time of embryonic‐type ACh channels in Xenopus cultured myocytes. In the present study, we further investigated the interaction between these two kinases in the modulation of ACh channels by using the receptor ligands, adenosine diphosphate (ADP) and calcitonin gene‐related peptide (CGRP) which selectively activate PKC and PKA, respectively.
ADP concentration‐dependently increased the mean open time of embryonic‐type ACh channels and 0.3 mM ADP is sufficient to achieve the maximal potentiating effect, α, β‐Methylene ATP and PMA (phorbol 12‐myristate 13‐acetate) but not adenosine, AMP, dibutyryl cyclic GMP have similar potentiating action.
Suramin (0.3 mM) pretreatment abolished the potentiating effect of ADP but left that of PMA unchanged.
CGRP increased the mean open time of embryonic‐type ACh channels in a concentration‐dependent manner and 1 μm CGRP produced the maximal effect.
The maximal effects of both ADP (0.3 mM) and CGRP (1 μm) in the prolongation of mean open time of ACh channels were additive.
These results suggest that the modulation of embryonic‐type ACh channels by the endogenously released ligands via the activation of PKA and PKC is additive and possibly different sites of ACh channels may be involved in the potentiation effect of either PKC or PKA.
Protein kinase C in rat brain cortex and hippocampus: effect of repeated administration of fluoxetine and desipramine
Authors: Mann Catherine D. , Vu T. Bich , Hrdina Pavel D. 
Published: July 2012

Recent evidence indicates that changes in the activity of cyclic AMP‐dependent protein kinase may be involved in neuroadaptive mechanisms after chronic treatment with antidepressants. The aim of this study was to investigate the effect of repeated administration of fluoxetine (FL) and desipramine (DMI) on the distribution and activity of protein kinase C (PKC) in subcellular fractions of rat cortex (Cx) and hippocampus (Hc) under basal conditions and in response to a single in vivo administration of 5‐HT2A/2C agonist, 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI).
Rats were treated for 21 days with FL (5 mg kg−1 day−1, i.p.) or DMI (10 mg kg−1 day−1, i.p.). DOI was injected to groups of rats receiving repeated doses of antidepressants or to control rats 1 h before ex vivo PKC assay. Distribution of PKC was determined by [3H]‐phorbol‐12,13‐dibutyrate ([3H]‐PDBu) binding and PKC activity by the Amersham enzyme assay system.
Autoradiography of tissue sections revealed decreased [3H]‐PDBu binding in CA1 region of hippocampus (by 18%) and paraventricular thalamic nucleus (by 28%) of rats after repeated administration of FL.
In vitro exposure of brain sections to 50 μm FL resulted in significant decreases (by 23–32%) of [3H]‐PDBu binding in six out of seven regions examined; exposure to 100 μm FL reduced [3H]‐PDBu binding (by 36–52%) in all regions. In contrast, exposure of brain sections to 100 μm DMI failed to alter specific [3H]‐PDBu binding in brain sections.
The activity of PKC in subcellular fractions of Cx and Hc was significantly (by 40–50%) decreased in rats given repeated doses of FL or DMI. A single administration of either drug was without effect.
A single in vivo administration of DOI to control rats resulted in reduced PKC activity (by 30–40%) in the particulate fraction of both Cx and Hc. This response to DOI was similar in DMI‐treated rats but was not seen in rats given repeated doses of FL. A single administration of DOI to animals given repeated doses of FL resulted in PKC activities higher than those seen in rats treated with FL alone.
The results indicate that repeated administration of FL and DMI produced similar changes in basal PKC activity but differentially affected the PKC response to the 5‐HT2A/2C receptor agonist, DOI. The effect on basal PKC activity may result from a post‐receptor action of antidepressants; the alteration of PKC response to DOI after fluoxetine could be due to receptor‐mediated desensitization of the signalling system.
The involvement of ATP‐sensitive potassium channels in β‐adrenoceptor‐mediated vasorelaxation in the rat isolated mesenteric arterial bed
Authors: Randall Michael D. , McCulloch Audrey I. 
Published: July 2012

We have used the isolated buffer‐perfused superior mesenteric arterial bed of the rat to assess the involvement of ATP‐sensitive potassium (KAtp) channels in the vasorelaxant responses to β‐adrenoceptor agonists.
The vasorelaxant potencies of the non‐selective β‐adrenoceptor agonist, isoprenaline, the β1 adrenoceptor agonist, dobutamine and the β2‐adrenoceptor agonist, terbutaline were all significantly (P>0.05) reduced (isoprenaline, ED50=265±31 pmol v. 1.05 ± 0.42 nmol; dobutamine, ED50=294± 67 pmol v. 497 ± 115 pmol; terbutaline, ED50= 157 ±26 nmol v. 452 ± 120 nmol) in the presence of the KATP‐channel blocker, glibenclamide.
The presence of glibenclamide only weakly influenced the vasorelaxant properties of salbutamol, a β2‐adrenoceptor agonist, while those of verapamil, a β‐adrenoceptor‐independent vasorelaxant, were unaffected.
In radioligand binding experiments, glibenclamide (1 nM‐100 μm) did not displace any specific [3H]‐dihydroalprenolol binding from rat β‐adrenoceptors. Therefore, glibenclamide does not bind to β‐adrenoceptors at the concentration used in the present investigation.
Vasorelaxant responses to dibutyryl cyclic AMP, the cell permeable analogue of cyclic AMP, were also unaffected by glibenclamide, indicating that the coupling of β‐adrenoceptors to KATP‐channels occurs independently of the elevation of intracellular cyclic AMP.
We have shown that a significant element of the vasorelaxant responses to both β1 and β2 adrenoceptor activation involves the opening of KATP‐channels. In conclusion, KATP‐channels may play a physiological role in β‐adrenoceptor‐mediated vasodilatation.
Polydeoxyribonucleotides and nitric oxide release from guinea‐pig hearts during ischaemia and reperfusion
Authors: Masini E. , Lupini M. , Mugnai L. , Raspanti S. , Mannaioni P.F. 
Published: July 2012

Two polydeoxyribonucleotides, produced by the controlled hydrolysis of DNA of mammalian lung (defibrotide and its lower molecular weight fraction, P.O. 085 DV), were studied for their ability to modify the release of nitrite and the coronary flow in perfusates collected from isolated, normally perfused hearts of guinea‐pigs and from hearts subjected to regional ischaemia and reperfusion.
In guinea‐pig normally perfused hearts, both defibrotide (DFT) and its fraction, P.O. 085 DV, increase the amount of nitrite appearing in perfusates in a concentration‐dependent fashion. At the highest concentration studied (10−6 m), P.O. 085 DV was more effective than DFT. A concomitant increase in the coronary flow was observed.
The increase in nitrite in perfusates and the increase in coronary flow induced by both DFT and P.O. 085 DV were significantly reduced by NGmonomethyl‐L‐arginine (l‐NMMA, 10−4 m), an inhibitor of nitric oxide synthase (NOS).
The endothelium‐dependent vasodilator, acetylcholine (ACh), enhances the formation of nitrite and the coronary flow. Both the increase in coronary flow and in the formation of nitrite were significantly reduced by L‐NMMA (10−4 m).
In guinea‐pig hearts subjected to ischaemia and reperfusion, the effect of both compounds in increasing the amount of nitrite in perfusates was more evident and more pronounced with P.O. 085 DV.
Reperfusion‐induced arrhythmias were significantly reduced by both compounds to the extent of complete protection afforded by compound P.O. 085 DV.
The cardioprotective and antiarrhythmic effects of DFT and P.O. 085 DV are discussed.
Mechanism of bradykinin‐induced plasma extravasation in the rat knee joint
Authors: Cambridge H. , Brain S.D. 
Published: July 2012

We have investigated the mechanism of bradykinin (BK)‐induced plasma extravasation into the knee joint of the anaesthetized rat. Accumulation of [125I]‐human serum albumin within the synovial cavity was used as a marker of increased vascular permeability.
Perfusion with BK (1 μm) produced significant plasma extravasation into the knee which was inhibited by co‐perfusion of the selective bradykinin B2 receptor antagonist D‐Arg‐[Hyp3, Thi5, D‐Tic7Oic8]‐bradykinin (Hoe 140, 200 nM).
The bradykinin B1 receptor agonist, [des‐Arg9]‐BK (up to 100 mM), did not induce plasma extravasation into the knee joint over this time period.
Chemical sympathectomy by chronically administered 6‐hydroxydopamine (6‐OHDA) did not inhibit bradykinin‐induced plasma extravasation. Acute intra‐articular perfusion with 6‐OHDA (to stimulate transmitter release from sympathetic nerve terminals) at concentrations up to 50 mM did not induce significant plasma extravasation. Intra‐articular perfusion of 100 mM 6‐OHDA induced significant plasma extravasation but produced severe systemic toxicity.
The selective neurokinin1 (NK1) receptor antagonist, RP67580 (230 nmol kg−1), or receptor antagonists for the mast cell products histamine and 5‐hydroxytryptamine did not significantly inhibit BK‐induced plasma extravasation.
Co‐perfusion of the NO synthase inhibitor, NG‐nitro‐L‐arginine methyl ester (L‐NAME) (1 mM) did not significantly inhibit the response to BK. 133Xe clearance from L‐NAME (1 mM)‐injected joints was significantly (P < 0.05) reduced compared to D‐NAME injected joints, suggesting a reduction in blood flow as a result of decreased basal NO production. Systemic administration of L‐NAME at doses sufficient to produce significant and sustained elevation of blood pressure (5 or 30 mg kg−1, i.v. 15 min prior to BK perfusion) also failed to significantly inhibit the BK‐induced response.
We conclude that, in normal joints, BK induces plasma extravasation by acting on bradykinin B2 receptors and that this response is not dependent on secondary release of mediators from sympathetic nerve terminals, sensory nerves, mast cells or on generation of NO.
Effects of mastoparan upon the late stages of the ACTH secretory pathway of AtT‐20 cells
Authors: McFerran Brian W. , Guild Simon B. 
Published: July 2012

The mouse AtT‐20/D16‐16 anterior pituitary tumour cell line was used as a model system for the study of the effects of mastoparan upon the late stages of the adrenocorticotrophin (ACTH) secretory pathway.
Mastoparan (10−8‐10−5 m), an activator of heterotrimeric guanosine 5′‐triphosphate binding proteins (G‐proteins), stimulated ACTH secretion from electrically‐permeabilized AtT‐20 cells in a concentration‐dependent manner in the effective absence of calcium ions with a threshold of 10−6 m. Guanosine 5′‐0‐(3‐thiotriphosphate) (GTP‐γ‐S) (10−8‐10−4m) also stimulated ACTH secretion from electrically‐permeabilized AtT‐20 cells in a concentration‐dependent manner in the effective absence of calcium ions with a threshold of 10−6 m. This GTP‐γ‐S‐evoked secretion is consistent with previous studies which demonstrated that a G‐protein, termed GE, mediates calcium evoked ACTH secretion from AtT‐20 cells. GTP‐γ‐S‐evoked secretion however was not as great as that obtained in response to mastoparan.
Both mastoparan (10−5 m) and GTP‐γ‐S (10−4m) stimulated ACTH secretion from electrically‐permeabilized AtT20 cells in a time‐dependent manner. A time of 30 min was adopted as the standard incubation period for the study of both mastoparan and GTP‐γ‐S‐stimulated ACTH secretion from permeabilized AtT‐20 cells.
Mastoparan (10−8‐10−5 m) stimulated ACTH secretion from permeabilized AtT‐20 cells to the same extent in the presence and absence of the protein kinase C (PKC) inhibitor, chelerythrine chloride (10−5 m).
Mastoparan (10−8‐10−5 m)‐stimulated ACTH secretion from permeabilized AtT‐20 cells was significantly reduced in the presence of guanosine 5′‐0‐(2‐thiodiphosphate) (GDP‐β‐S, 10−4 m).
The mastoparan analogue, Mas‐7 (10−8‐10−5m) stimulated ACTH secretion from permeabilized AtT‐20 cells to a greater extent than mastoparan (10−8‐10−5m) however, the mastoparan analogue Mas‐17 (10−8‐10−5 m) had no effect upon ACTH secretion from permeabilized AtT‐20 cells.
Mastoparan (10−8‐10−5m) stimulated ACTH secretion from permeabilized AtT‐20 cells in the presence and absence of ATP, normally present in the standard permeabilization medium at a concentration of 5 mM. Mastoparan (10−8‐10−5 m)‐stimulated ACTH secretion as well as control secretion was reduced when ATP was omitted.
The results of the present study demonstrate that mastoparan stimulated ACTH secretion from permeabilized AtT‐20 cells and displayed characteristics consistent with calcium ion‐ and GTP‐γ‐S‐stimulated ACTH secretion from permeabilized AtT‐20 cells. This suggests that in permeabilized AtT‐20 cells, mastoparan directly activates GE and that this G‐protein may be a heterotrimeric G‐protein. This study also suggests mastoparan may be a useful alternative to GTP‐γ‐S as a means of directly activating GE.
Increase of noradrenaline release in the hypothalamus of freely moving rat by postsynaptic 5‐hydroxytryptamine1A receptor activation
Authors: Suzuki M. , Matsuda T. , Asano S. , Somboonthum P. , Takuma K. , Baba A. 
Published: July 2012

5‐Hydroxytryptamine (5‐HT) plays a role in the regulation of noradrenergic neurones in the brain, but the precise mechanism of regulation of noradrenaline (NA) release by 5‐HT1A receptors has not been defined. The present study describes the effect of a highly potent and selective 5‐HT1A receptor agonist, 5‐{3‐[[(2S)‐1,4‐benzodioxan‐2‐ylmethyl]amino]propoxy}‐1,3‐benzodioxole HC1 (MKC‐242), on NA release in the hypothalamus using microdialysis in the freely moving rat.
Subcutaneous injection of MKC‐242 (0.5mg kg_1) increased extracellular levels of NA and its metabolite, 3‐methoxy‐4‐hydroxyphenylglycol, in the hypothalamus and hippocampus.
The 5‐HT1a receptor agonists, 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT) (0.2 mg kg−1) and buspirone (3 mg kg−1) mimicked the effect of MKC‐242 in increasing NA release in the hypothalamus.
The effects of MKC‐242 and 8‐OH‐DPAT in the hypothalamus were antagonized by pretreatment with WAY100135 (10 mg kg−1), a silent 5‐HT1A receptor antagonist.
Local administration of 8‐OH‐DPAT (10–100 μm), citalopram (1 μm), a 5‐HT reuptake inhibitor, and MDL72222 (10 μm), a 5‐HT3 receptor antagonist, into the hypothalamus, had no effect on NA release.
Intracerebroventricular injection with 5,7‐dihydroxytryptamine caused a marked reduction in brain 5‐HT content, but the treatment affected neither basal NA levels nor the MKC‐242‐induced increase in NA release.
The effect of MKC‐242 in increasing NA release was not attenuated by repeated treatment with the drug (0.5 mg kg−1, once a day for 2 weeks).
The present results suggest that activation of postsynaptic 5‐HT1A receptors increases NA release in the hypothalamus.