bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natriuretic peptide‐induced cyclic GMP accumulation in adult guinea‐pig cerebellar slices
Authors: Hernández Félix , Alexander Stephen P.H. , Kendall David A. 
Published: July 2012

Second messenger responses to natriuretic peptides were studied in guinea‐pig cerebellar slices by use of radioactive precursors.
The rank order of potency of the different natriuretic peptides in generating [3H]‐guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) was atrial natriuretic peptide (ANP) > brain natriuretic peptide (BNP) > C‐type natriuretic peptide (CNP) with EC50 values of 19.5 ± 8.8 nM for ANP and 169 ± 41 nM for BNP. CNP induced [3H]‐cyclic GMP accumulation only at concentrations greater than 1 μm.
An additive response to ANP (1 μm) was observed in the presence of the adenosine receptor agonist, 5′‐N‐ethylcarboxamidoadenosine (NECA, 10 μm) or the soluble guanylyl cyclase activator, sodium nitroprusside (SNP, 100 μm) for [3H]‐cyclic GMP accumulation.
ANP, BNP and CNP (all at 1 μm) failed to alter significantly either basal‐, forskolin‐ (10 μm), isoprenaline‐ (100 μm), or NECA‐ (10 μm) induced [3H]‐cyclic AMP generation. Natriuretic peptides also did not change the [3H]‐cyclic AMP steady‐state reached after 10 min of treatment with 10 μm forskolin.
Natriuretic peptides failed to elicit significant accumulation of [3H]‐inositol phosphates at concentrations up to 10 μm.
These data are consistent with the presence of ANPA, rather than ANPB or clearance receptors (C‐receptors), linked to second messenger cascades in guinea‐pig cerebellar slices.
Antagonism by riluzole of entry of calcium evoked by NMDA and veratridine in rat cultured granule cells: evidence for a dual mechanism of action
Authors: Hubert J.P. , Delumeau J.C. , Glowinski J. , Prémont J. , Doble A. 
Published: July 2012

Intracellular calcium levels were measured in cultured cerebellar granule cells of the rat by use of the fluorescent dye, indo‐1/AM.
Intracellular calcium levels were increased by depolarizing stimuli such as N‐methyl‐d‐aspartate (NMDA) (100 μm), glutamic acid (20 μm), and veratridine (10 μm). This increase was essentially due to entry of external calcium.
Riluzole (10 μm) blocked responses to all the depolarizing agents.
Riluzole could still block the increase in intracellular calcium evoked by NMDA or glutamic acid when sodium channels were blocked by tetrodotoxin, suggesting that this effect is not mediated by a direct action of riluzole on the voltage‐dependent sodium channel.
Pretreatment of the cells with pertussis toxin (0.1 μg ml−1) did not modify the increases in intracellular calcium evoked by NMDA, glutamic acid or veratridine.
In pertussis toxin‐treated cells, riluzole could no longer block responses to excitatory amino acids, but still blocked responses to veratridine.
It is concluded that riluzole has a dual action on cerebellar granule cells, both blocking voltage‐dependent sodium channels and interfering with NMDA receptor‐mediated responses via a pertussis toxin‐sensitive mechanism. Furthermore, these two processes have been shown to be independent.
Pharmacological characteristics of liriodenine, isolated from Fissistigma glaucescens, a novel muscarinic receptor antagonist in guinea‐pigs
Authors: Lin Chien‐Huang , Chang Gwo‐Jyh , Su Ming‐Jai , Wu Yang‐Chang , Teng Che‐Ming , Ko Feng‐Nien 
Published: July 2012

The pharmacological activities of liriodenine, isolated from Fissistigma glaucescens, were determined in isolated trachea, ileum and cardiac tissues of guinea‐pigs.
Liriodenine was found to be a muscarinic receptor antagonist in guinea‐pig trachea as revealed by its competitive antagonism of carbachol (pA2 = 6.22 ± 0.08)‐induced smooth muscle contraction. It was slightly more potent than methoctramine (pA2 = 5.92 ± 0.05), but was less potent than atropine (pA2 = 8.93 ± 0.07), pirenzepine (pA2 = 7.02 ± 0.09) and 4‐diphenylacetoxy‐N‐methylpiperidine (4‐DAMP, pA2 = 8.72 ± 0.07).
Liriodenine was also a muscarinic antagonist in guinea‐pig ileum (pA2 = 6.36 ± 0.10) with a pA2 value that closely resembled that obtained in the trachea.
Liriodenine was 10 fold less potent in atrial preparations (left atria, pA2 = 5.24 ± 0.04; right atria, pA2 = 5.35 ± 0.09 and 5.28 ± 0.07 for inotropic and chronotropic effects, respectively) than in smooth muscle preparations.
High concentration of liriodenine (300 μm) partially depressed the contractions induced by U‐46619, histamine, prostaglandin F2a, neurokinin A, leukotriene C4 and high K+ in the guinea‐pig trachea. The inhibitions were characterized by a rightward shift in the concentration‐response curves with suppression of their maximal contraction.
High concentration of liriodenine (300 μm) did not affect U‐46619‐ or neurokinin A‐induced tracheal contraction in the presence of nifedipine (1 μm) or in Ca2+‐free (containing 0.2 mm EGTA) medium.
Neither cyclic AMP nor cyclic GMP content of guinea‐pig trachealis was changed by liriodenine (30–300 μm).8 It is concluded that liriodenine is a selective muscarinic receptor antagonist in isolated trachea, ileum and cardiac tissues of guinea‐pigs. It is more potent in smooth muscle than in cardiac preparations. It also acts as a blocker of voltage‐dependent Ca2+ channels at a high concentration (300 μm).
Effects of caffeine on intracellular sodium activity in cardiac Purkinje fibres: relation to force
Authors: Iacono Giovanni , Vassalle Mario 
Published: July 2012

An increase in cytoplasmic calcium by caffeine would lead to Ca extrusion via the Na/Ca exchange. The hypotheses were investigated that, as a consequence, caffeine might increase intracellular sodium activity (aiNa) and that the relation between aiNa and force might be conditioned by the Ca load.
Action potential, aiNa and contractile force were recorded in sheep Purkinje fibres during exposure to caffeine under conditions that decrease or increase the Ca load by different mechanisms.
In Tyrode solution, caffeine (8 mm) increased aiNa from 8.05 ± 0.20 to 10.52 ± 0.40 mm (+ 30.5%) and had a triphasic effect on force: an initial transient increase (+ 93.6%), a subsequent decrease (‐37.1%) (negative inotropy) and slow partial recovery (+8.9%).
Decreasing the Ca load by means of manganese (1 mm) decreased aiNa and force. Adding caffeine re‐increased aiNa and no longer caused a negative inotropic action. Cadmium (0.2 mm) also decreased aiNa, and caffeine reincreased it although far less than in Tyrode solution.
High [K]o (10 mm) and tetrodotoxin (5 μm) decreased aiNa as well as force. In their presence, caffeine re‐increased aiNa and no longer had a negative inotropic action.
Increasing the Ca load by means of high [Ca]o (8.1 mm) increased force (+ 195%) and decreased aiNa, (‐20.3%). Adding caffeine re‐increased aiNa (+ 28.1%), but immediately decreased force (‐32.3%).
Addition of pyruvate (10 mm) to caffeine increased force, as it does in the presence of Ca overload.
Noradrenaline (0.1–1 μm) decreased aiNa and increased contractile force. In its presence, caffeine decreased aiNa further and increased force.
It is concluded that caffeine increases aiNa, even during the negative inotropic effect. The decrease in force appears to depend on Ca load. Thus, caffeine no longer decreases force under conditions that decrease Ca load (Mn, high [K]o, TTX) and immediately decreases force when the Ca load is increased (high [Ca]o). However, in the presence of noradrenaline, caffeine decreases aiNa and markedly increases force, as the Ca load is increased, but Ca can be removed from the cytoplasm into the SR.
Involvement of enzymatic degradation in the inactivation of tachykinin neurotransmitters in neonatal rat spinal cord
Authors: Suzuki H. , Yoshioka K. , Yanagisawa M. , Urayama O. , Kurihara T. , Hosoki R. , Saito K. , Otsuka M. 
Published: July 2012

The possible involvement of enzymatic degradation in the inactivation of tachykinin neurotransmitters was examined in the spinal cord of the neonatal rat.
The magnitude of substance P (SP)‐ or neurokinin A (NKA)‐evoked depolarization of a lumbar ventral root in the isolated spinal cord preparation was increased by a mixture of peptidase inhibitors, consisting of actinonin (6 μm), arphamenine B (6 μm), bestatin (10 μm), captopril (10 μm) and thiorphan (0.3 μm). The mixture augmented the response to NKA more markedly than that to SP.
In the isolated spinal cord‐cutaneous nerve preparation, the saphenous nerve‐evoked slow depolarization of the L3 ventral root was augmented by the mixture of peptidase inhibitors in the presence of naloxone (0.5 μm) but not in the presence of both naloxone and a tachykinin receptor antagonist, GR71251 (5 μm).
Application of capsaicin (0.5 μm) for 6 min to the spinal cord evoked an increase in the release of SP from the spinal cord. The amount of SP released was significantly augmented by the mixture of peptidase inhibitors.
Synaptic membrane fractions were prepared from neonatal rat spinal cords. These fractions showed degrading activities for SP and NKA and the activities were inhibited by the mixture of peptidase inhibitors. The degrading activity for NKA was higher than that for SP and the inhibitory effect of the mixture for NKA was more marked than that for SP. Although some other fractions obtained from homogenates of spinal cords showed higher degrading activities for SP, these activities were insensitive to the mixture of peptidase inhibitors.
Effects of individual peptidase inhibitors on the enzymatic degradation of SP and NKA by synaptic membrane fractions were examined. Thiorphan, actinonin and captopril inhibited SP degradation, while thiorphan and actinonin, but not captopril, inhibited NKA degradation. The potency of the inhibition of each peptidase inhibitor was lower than that of the mixture.
The present results suggest that enzymatic degradation is involved in the inactivation of tachykinin neurotransmitters in the spinal cord of the neonatal rat.
5‐HT3 receptor antagonism by anpirtoline, a mixed 5‐HT1 receptor agonist/5‐HT3 receptor antagonist
Authors: Göthert M. , Hamon M. , Barann M. , Bönisch H. , Gozlan H. , Laguzzi R. , Metzenauer P. , Nickel B. , Szelenyi I. 
Published: July 2012

The aim of this study was to provide evidence that anpirtoline, which is an agonist at 5‐HT1B and 5‐HT1D receptors and also displays submicromolar affinity for 5‐HT1A recognition sites, in addition, acts as an antagonist at 5‐HT3 receptors.
In radioligand binding studies on rat brain cortical membranes, anpirtoline inhibited specific binding of [3H]‐(S)‐zacopride to 5‐HT3 receptor recognition sites (pKi: 7.53).
In N1E‐115 neuroblastoma cells in which [14C]‐guanidinium was used as a tool to measure cation influx through the 5‐HT3 > receptor channel, the 5‐HT‐induced influx was concentration‐dependently inhibited by anpirtoline. In this respect, anpirtoline mimicked other 5‐HT3 receptor antagonists; the rank order of potency was ondansetron>anpirtoline>metoclopramide.
The concentration‐response curve for 5‐HT as a stimulator of [14C]‐guanidinium influx was shifted to the right by anpirtoline (apparent pA2: 7.78).
In urethane‐anaesthetized rats, anpirtoline inhibited (at lower potency than zacopride and tropisetron) the 5‐HT‐ or phenylbiguanide‐induced bradycardia (Bezold‐Jarisch reflex), but did not induce this reflex by itself.
Intravenous infusion of cisplatin in the domestic pig caused a consistent emetic response which was antagonized by anpirtoline.
It is concluded that anpirtoline, which was previously characterized as a 5‐HT1 receptor agonist also proved to be a 5‐HT3 receptor antagonist in several experimental models and, hence, exhibits a unique pattern of properties at different 5‐HT receptors.
Inhibition by dizocilpine (MK‐801) of striatal dopamine release induced by MPTP and MPP+: possible action at the dopamine transporter
Authors: Clarke P.B.S. , Reuben M. 
Published: July 2012

The NMDA‐type glutamate receptor antagonist, dizocilpine (MK‐801) can protect against neurotoxicity associated with 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) and its principal metabolite, the 1‐methyl‐4‐phenylpyridinium ion (MPP+). It has been suggested that these neurotoxic effects may be mediated by release of excitatory amino acids, but possible alternative mechanisms have been little investigated.
MPTP and MPP+ (0.1–1000 μm) were tested in superfused rat striatal synaptosomes preloaded with [3H]‐dopamine. Both MPTP (10 μm and higher) and MPP+ (1 μm and higher) evoked an immediate and concentration‐dependent release of [3H]‐dopamine. The maximal effect exceeded that achievable with nicotine. For subsequent experiments, submaximal concentrations of MPTP (50 μm) and MPP+ (10 μm) were tested.
MK‐801 (0.1–100 μm) inhibited responses to MPTP (50 μm) and MPP+ (10 μm) in a concentration‐dependent manner. However, further tests of NMDA‐type glutamate receptor involvement proved negative. Responses to MPTP or MPP+ were unaffected by the omission of Mg2+ or Ca2+ and were not reduced by the NMDA receptor antagonists, AP‐7 (200 μm) and kynurenic acid (300 μm). In this assay, N‐methyl‐d‐aspartate (even in the absence of Mg2+ and with added glycine and strychnine) did not evoke [3H]‐dopamine release.
In crude membrane preparations of rat cerebral cortex, MPTP and MPP+ inhibited high‐affinity [3H]‐nicotine binding to nicotinic cholinoceptors (IC50 1.8 μm and 26 μm, respectively).
[3H]‐dopamine release evoked by nicotine (1 μm) was blocked by the nicotinic antagonists, mecamylamine and chlorisondamine, and by MK‐801 (all at 100 μm); K+‐evoked release was not affected. Release evoked by MPTP and MPP+ was significantly attenuated by MK‐801 but not by mecamylamine or chlorisondamine.
At a high concentration (10 μm), the selective dopamine uptake inhibitor, nomifensine, completely blocked [3H]‐dopamine release evoked by amphetamine 0.3 μm and MPP+ 10 μm, attenuated responses to MPTP 50 μm and did not affect responses to 12 mm K+. MK‐801 100 μm evinced a similar profile but was less effective.
MK‐801 inhibited [3H]‐dopamine uptake in striatal synaptosomes with an IC50 of 115 μm.
It is concluded that high concentrations of MK‐801 inhibit the acute dopamine release evoked by MPTP and MPP+ in synaptosomes. This antagonism may occur, at least in part, through inhibition of the cell membrane dopamine transporter. MPTP and MPP+ also appear to interact with brain nicotinic cholinoceptors but the functional consequences of this interaction are not yet clear.
Mechanism of activation of nonselective cation channels by putative M4 muscarinic receptor in guinea‐pig chromaffin cells
Authors: Inoue Masumi , Imanaga Itsusei 
Published: July 2012

Mechanisms involved in the generation of nonselective cation currents (INS) by muscarinic agonists in the chromaffin cell were investigated by the perforated patch method.
Bath application of muscarine (0.1–30 μm) produced an inward INS with or without a transient outward current at −40 mV, whereas oxotremorine (0.06–60 μm) induced INS alone. Rectangular hyperbolas with EC50S of 2.01 and 0.21 μm were fitted to muscarine‐ and oxotremorine‐induced INSs, respectively, and the maximal amplitude of the former was about 3.4 times larger than that of the latter.
In 36% of the cells exposed to Ca2+‐free solution, muscarine INS was suppressed, being 53% of control 20 min after the perfusion, and in four cells that were incubated with Ca2+‐free solution for 2 h or more, the INS averaged 44% of that induced subsequently in normal solution. In contrast, muscarine INS was enhanced by about 30% when A‐23187 was added to normal solution.
W‐7 and W‐5, calmodulin‐related agents, were almost equally potent in inhibiting muscarine INS, whereas compound 5, a potent inhibitor of calmodulin‐dependent kinase II (CaM kinase II), produced no evident inhibition.
HA 1004, a weak kinase C inhibitor, induced a reversible suppression of muscarine INS with an IC50 of 163 μm, whereas H‐8, another kinase inhibitor, produced an even small degree of inhibition. Administration of phorbol 12, 13‐dibutyrate did not mimic muscarinic stimulation of NS channels; rather, it led to a progressive inhibition of INS and this inhibition was almost complete within 20 min. An inactive phorbol ester had no such effect.
The muscarinic antagonists, pirenzepine and AF‐DX 116, shifted the dose‐response curve for the muscarine INS to the right in a parallel manner. The KDS for pirenzepine and AF‐DX 116 were estimated to be 13 nm (95% confidence interval, 11–16 nm) and 365 nm (283–470 nm), respectively.
These results suggest that muscarine efficiently produces INS, probably through binding to the M4 subtype, that intracellular Ca2+ has a facilitating, but not an essential role in the generation of INS, and that neither CaM kinase II nor protein kinase C is involved.
Necessity of protein kinase C activity for maintenance of acetylcholine receptor function at snake twitch fibre endplates
Authors: Hardwick Jean C. , Parsons Rodney L. 
Published: July 2012

The extent of recovery of endplate sensitivity following a 5 or 10 min exposure to carbachol was determined from measurements of miniature endplate current (m.e.p.c.) amplitudes in voltage‐clamped snake twitch fibre endplates. M.e.p.c. amplitude recovery was dependent on the carbachol concentration (0.27–5.4 mm) and duration of application. Staurosporine pretreatment (0.5 μm for ∼15 min) further decreased the extent of m.e.p.c. amplitude recovery.
The decrease in m.e.p.c. amplitude at control endplates exposed to high concentrations of agonist (5.4 mm carbachol for 10 min) was due to an apparent decrease in postsynaptic receptor density, not to a change in the conductance of the acetylcholine (ACh)‐activated channels.
Pretreatment with either 1 μm lavendustin A or 50 μm KN‐62 had no effect on m.e.p.c. amplitude recovery, whereas pretreatment with either 0.5 μm staurosporine, 50 μm sphingosine, or 0.5 μm calphostin C significantly reduced m.e.p.c. amplitude recovery following carbachol exposure.
Sphingosine and staurosporine produced a concentration‐dependent decrease in the extent of m.e.p.c. amplitude recovery, but had no effect on m.e.p.c. characteristics in the absence of carbachol. In addition, this decrease in m.e.p.c. amplitude was not due to the presence of a subpopulation of small amplitude m.e.p.cs.
Prolonged treatment (18–20 h) of muscles with 200 nm phorbol 12‐myristate 13‐acetate (PMA), to down regulate protein kinase C, resulted in a significant reduction in m.e.p.c. amplitudes following exposure to carbachol. Conversely, treatment wtih 200 nm 4αPMA, an inactive analogue, had no effect on m.e.p.c. amplitude recovery.
Only large amplitude ACh‐activated channels (∼50 pS) were recorded from fibres either in the presence of 50 μm sphingosine or from fibres chronically exposed to PMA. However, following recovery from a 10 min exposure to 540 μm carbachol, both small conductance (∼25 pS) and large conductance ACh‐activated channels were recorded in both sphingosine‐ and phorbol‐treated preparations. The conductance of these two populations of channels was virtually identical to those seen in staurosporine‐treated fibres following carbachol exposure.
We conclude that protein kinase C is required for full recovery of AChR sensitivity following carbachol‐induced receptor inactivation. Exposure to high concentrations of agonist for prolonged periods appears to result in the inactivation of a subpopulation of receptors. These receptors must be replaced or reactivated by a process involving protein kinase C. When this phosphorylation step is inhibited, the AChRs remain in an activatable form, but with a reduced conductance.
Requirement of a colchicine‐sensitive component of the cytoskeleton for acetylcholine receptor recovery
Authors: Hardwick Jean C. , Parsons Rodney L. 
Published: July 2012

The effect of colchicine treatment on acetylcholine receptor function was examined in potassium depolarized, voltage‐clamped snake twitch fibre endplates. Receptor function was assessed by analysis of miniature endplate currents (m.e.p.c.) as well as acetylcholine (ACh)‐induced single channel currents.
Pretreatment of snake muscle fibres with colchicine (10 μm to 100 μm) for 16–18 h had no effect on m.e.p.c. amplitude or decay rates. At higher concentrations (1 mm), there was a slight decrease in the average m.e.p.c. amplitude.
Colchicine produced a concentration‐dependent decrease in the extent of m.e.p.c. amplitude recovery following a 10 min exposure to 540 μm carbachol. Exposure of 100 μm colchicine‐treated preparations to 0.5 μm staurosporine further reduced the extent of m.e.p.c. amplitude recovery following carbachol exposure.
The decrease in m.e.p.c. amplitude following carbachol exposure was not due to a shift in the m.e.p.c. reversal potential. In addition, the distribution of m.e.p.c. amplitudes remained unimodal in both control and colchicine (100 μm)‐treated preparations following carbachol exposure.
In addition to the normal, large conductance (∼48 pS) ACh‐activated channels, a population of small conductance (∼29 pS) channels was observed in colchicine‐treated preparations following exposure to carbachol. In preparations treated with both colchicine and staurosporine and then exposed to carbachol, the conductance of these small channels was identical to that of colchicine or staurosporine alone.
We suggest that prolonged exposure of snake twitch fibre endplates to agonist results in the activation and desensitization of ACh receptors. Furthermore, we propose that for a subpopulation of the inactivated receptors, restoration of function requires both the integrity of a subsynaptic cytoskeletal component and phosphorylation by a staurosporine‐sensitive protein kinase. One plausible mechanism is that some receptors become destabilized in the membrane and phosphorylation of a cytoskeletal component, whose distribution may depend on an intact microtubular system, is required to re‐anchor these receptors. If this anchoring process is inhibited either by disruption of the cytoskeleton with colchicine, or inhibition of the kinase by staurosporine, these receptors remain activatable, but have a reduced conductance.