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Muscle Preparations (muscle + preparation)
Selected AbstractsAnti-disialosyl antibodies mediate selective neuronal or Schwann cell injury at mouse neuromuscular junctionsGLIA, Issue 3 2005Susan K. Halstead Abstract The human paralytic neuropathy, Miller Fisher syndrome (MFS) is associated with autoantibodies specific for disialosyl epitopes on gangliosides GQ1b, GT1a, and GD3. Since these gangliosides are enriched in synaptic membranes, anti-ganglioside antibodies may target neuromuscular junctions (NMJs), thereby contributing to disease symptoms. We have shown previously that at murine NMJs, anti-disialosyl antibodies induce an ,-latrotoxin-like effect, electrophysiologically characterized by transient massive increase of spontaneous neurotransmitter release followed by block of evoked release, resulting in paralysis of the muscle preparation. Morphologically, motor nerve terminal damage, as well as perisynaptic Schwann cell (pSC) death is observed. The relative contributions of neuronal and pSC injury to the paralytic effect and subsequent repair are unknown. In this study, we have examined the ability of subsets of anti-disialosyl antibodies to discriminate between the neuronal and glial elements of the NMJ and thereby induce either neuronal injury or pSC death. Most antibodies reactive with GD3 induced pSC death, whereas antibody reactivity with GT1a correlated with the extent of nerve terminal injury. Motor nerve terminal injury resulted in massive uncontrolled exocytosis with paralysis. However, pSC ablation induced no acute (within 1 h) electrophysiological or morphological changes to the underlying nerve terminal. These data suggest that at mammalian NMJs, acute pSC injury or ablation has no major deleterious influence on synapse function. Our studies provide evidence for highly selective targeting of mammalian NMJ membranes, based on ganglioside composition, that can be exploited for examining axonal,glial interactions both in disease states and in normal NMJ homeostasis. © 2005 Wiley-Liss, Inc. [source] Effects of Temporal Application Parameters on Lesion Dimensions During Transvenous Catheter CryoablationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2 2005HUNG-FAT TSE M.D. Background: Transvenous catheter cryoablation is a novel technique for treating cardiac arrhythmias. However, the relative importance of temporal application parameters on lesion dimension and clinical efficacy has not been studied. Methods and Results: We investigated the effects of (1) application duration: single 2.5 (2.5 × 1) versus single 5 versus double 2.5 (2.5 × 2) versus double 5 (5 × 2) minutes, (2) number of freeze,thaw cycles: single versus double, and (3) electrode contact area: horizontal versus vertical orientation, on the lesion diameter and depth during catheter cryoablation (10F, 6.5-mm tip-electrode, CryoCorÔ, San Diego) in a thigh muscle preparation. A total of 175 lesions (horizontal = 90, vertical = 85) were created in thigh muscle preparations on 10 swine. The lesion diameter and depth were significantly greater using 2.5 × 2 and 5 × 2 application modes as compared with 2.5 × 1 applications (P < 0.05). Horizontal tip-electrode orientation produced larger lesion diameter (P < 0.05), but not lesion depth as compared with vertical orientation. Multivariate analysis demonstrated that both tip-electrode orientation and duration of freeze >2.5 minutes were independent predictors for lesion diameter (P < 0.001). However, only duration of freeze >2.5 minutes was an independent predictor for lesion depth (P < 0.001). Conclusions: The dimensions of lesions created by catheter cryoablation are affected by mode of cryoablation application and electrode orientation. Increasing the duration of application, employing multiple freeze,thaw cycles at shorter cycle durations, and orienting the catheter to enhance/increase tissue contact can create a larger lesion. [source] Spatial insulin signalling in isolated skeletal muscle preparationsJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 5 2010Peter Sogaard Abstract During in vitro incubation in the absence or presence of insulin, glycogen depletion occurs in the inner core of the muscle specimen, concomitant with increased staining of hypoxia-induced-factor-1-alpha and caspase-3, markers of hypoxia and apoptosis, respectively. The aim of this study was to determine whether insulin is able to diffuse across the entire muscle specimen in sufficient amounts to activate signalling cascades to promote glucose uptake and glycogenesis within isolated mouse skeletal muscle. Phosphoprotein multiplex assay on lysates from muscle preparation was performed to detect phosphorylation of insulin-receptor on Tyr1146, Akt on Ser473 and glycogen-synthases-kinase-3 on Ser21/Ser9. To address the spatial resolution of insulin signalling, immunohistochemistry studies on cryosections were performed. Our results provide evidence to suggest that during the in vitro incubation, insulin sufficiently diffuses into the centre of tubular mouse muscles to promote phosphorylation of these signalling events. Interestingly, increased insulin signalling was observed in the core of the incubated muscle specimens, correlating with the location of oxidative fibres. In conclusion, insulin action was not restricted due to insufficient diffusion of the hormone during in vitro incubation in either extensor digitorum longus or soleus muscles from mouse under the specific experimental settings employed in this study. Hence, we suggest that the glycogen depleted core as earlier observed is not due to insufficient insulin action. J. Cell. Biochem. 109: 943,949, 2010. © 2010 Wiley-Liss, Inc. [source] Nifedipine enhances cGMP production through the activation of soluble guanylyl cyclase in rat ventricular papillary muscleJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2005Kazuhiko Seya It is known that nifedipine, an L-type calcium channel blocker, increases cGMP production, which partially contributes to the relaxation of vascular smooth muscle. The aim of our investigation was to clarify whether or not nifedipine regulates cGMP production, which has a physiological role in cardiac muscle. To measure contractile responses and tissue cGMP levels, left ventricular papillary muscles prepared from male Wistar rats (350,400 g) were mounted in the isolated organ chamber under isometric conditions and electrically paced by means of platinum punctate electrodes (1 Hz, 1 ms duration). In papillary muscle preparation, the negative inotropic effect induced by nifedipine (30 to 300 nm) was significantly inhibited in the presence of ODQ (1H-[1,2,4]oxidazolo[4,3-a]quinoxaline-1-one; 10 ,m), a soluble guanylyl cyclase inhibitor. Furthermore, nifedipine (100 nm) strongly increased the tissue cGMP level, which was significantly decreased in the presence of ODQ. On the other hand, NG -monomethyl-l-arginine (100 ,m), a nitric oxide synthase inhibitor, did not inhibit either the negative inotropic effect or cGMP production induced by nifedipine. These results indicate that in rat left ventricular papillary muscle, nifedipine augments its negative inotropic effect at least partly through direct activation of cardiac soluble guanylyl cyclase but not nitric oxide synthase. [source] Proteomics of the rat gut: Analysis of the myenteric plexus-longitudinal muscle preparationPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 10 2005Laure Marvin-Guy Abstract The enteric nervous system (ENS) , present all along the gastrointestinal tract , is the largest and most complicated division of the peripheral nervous system that can function independently of the brain. The peripheral nerve cells are organized in two separate but interconnected meshworks, called the myenteric and submucous plexus. The nervous control of intestinal motility is primarily governed by the myenteric plexus (MP), which lies in-between the longitudinal- (LM) and circular-muscle layers and regulates their functions. To determine whether the proteomic technology is adapted to the analysis of specific gut tissues, we dissected the MP-LM layers from the jejunum, ileum, and colon of Long Evans rats, homogenized them, and separated the proteins using two-dimensional gel electrophoresis. A subset of all the visualized protein spots, covering the entire range of molecular weights and isoelectric points, was then selected and further analyzed by matrix-assisted laser desorption/ionization-time of flight and liquid chromatography mass spectrometry. We identified around 80 proteins in each gut segment, and among those, five were segment-specific. Most of the proteins identified were derived from muscle cells, but we also detected some neuron-specific proteins. This study represents, to our knowledge, the first extensive protein catalog of a neuromuscular layer of the rat intestine and it may constitute the basis to understand pathophysiological mechanisms related to the ENS. [source] Neurotoxic effects of venoms from seven species of australasian black snakes (Pseudechis): Efficacy of black and tiger snake antivenomsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2005Sharmaine Ramasamy SUMMARY 1.,Pseudechis species (black snakes) are among the most widespread venomous snakes in Australia. Despite this, very little is known about the potency of their venoms or the efficacy of the antivenoms used to treat systemic envenomation by these snakes. The present study investigated the in vitro neurotoxicity of venoms from seven Australasian Pseudechis species and determined the efficacy of black and tiger snake antivenoms against this activity. 2.,All venoms (10 µg/mL) significantly inhibited indirect twitches of the chick biventer cervicis nerve,muscle preparation and responses to exogenous acetylcholine (ACh; 1 mmol/L), but not to KCl (40 mmol/L), indicating activity at post-synaptic nicotinic receptors on the skeletal muscle. 3.,Prior administration of either black or tiger snake antivenom (5 U/mL) prevented the inhibitory effects of all Pseudechis venoms. 4.,Black snake antivenom (5 U/mL) added at t90 (i.e. the time-point at which the original twitch height was reduced by 90%) significantly reversed the effects of P. butleri (28 ± 5%), P. guttatus (25 ± 8%) and P. porphyriacus (28 ± 10%) venoms. Tiger snake antivenom (5 U/mL) added at the t90 time-point significantly reversed the neurotoxic effects of P. guttatus (51 ± 4%), P. papuanus (47 ± 5%) and P. porphyriacus (20 ± 7%) venoms. 5.,We show, for the first time, the presence of neurotoxins in the venom of these related snake species and that this activity is differentially affected by either black snake or tiger snake antivenoms. [source] Estimation of endogenous adenosine activity at adenosine receptors in guinea-pig ileum using a new pharmacological methodACTA PHYSIOLOGICA, Issue 2 2010K. F. Nilsson Abstract Aim:, Adenosine modulates neurotransmission and in the intestine adenosine is continuously released both from nerves and from smooth muscle. The main effect is modulation of contractile activity by inhibition of neurotransmitter release and by direct smooth muscle relaxation. Estimation of adenosine concentration at the receptors is difficult due to metabolic inactivation. We hypothesized that endogenous adenosine concentrations can be calculated by using adenosine receptor antagonist and agonist and dose ratio (DR) equations. Methods:, Plexus-containing guinea-pig ileum longitudinal smooth muscle preparations were made to contract intermittently by electrical field stimulation in organ baths. Schild plot regressions were constructed with 2-chloroadenosine (agonist) and 8-(p -sulfophenyl)theophylline (8-PST; antagonist). In separate experiments the reversing or enhancing effect of 8-PST and the inhibiting effect of 2-chloroadenosine (CADO) were analysed in the absence or presence of an adenosine uptake inhibitor (dilazep), and nucleoside overflow was measured by HPLC. Results:, Using the obtained DR, baseline adenosine concentration was calculated to 28 nm expressed as CADO activity, which increased dose dependently after addition of 10,6 m dilazep to 150 nm (P < 0.05). HPLC measurements yielded a lower fractional increment (80%) in adenosine during dilazep, than found in the pharmacological determination (440%). Conclusion:, Endogenous adenosine is an important modulator of intestinal neuro-effector activity, operating in the linear part of the dose,response curve. Other adenosine-like agonists might contribute to neuromodulation and the derived formulas can be used to calculate endogenous agonist activity, which is markedly affected by nucleoside uptake inhibition. The method described should be suitable for other endogenous signalling molecules in many biological systems. [source] D-2-Hydroxyglutaric acid inhibits creatine kinase activity from cardiac and skeletal muscle of young ratsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 10 2003C. G. Da Silva Abstract Background, Tissue accumulation of high amounts of D-2-hydroxyglutaric acid (DGA) is the biochemical hallmark of the inherited neurometabolic disorder D-2-hydroxyglutaric aciduria (DHGA). Patients affected by this disease usually present hypotonia, muscular weakness, hypothrophy and cardiomyopathy, besides severe neurological findings. However, the underlying mechanisms of muscle injury in this disorder are virtually unknown. Materials and methods, In the present study we have evaluated the in vitro role of DGA, at concentrations ranging from 0·25 to 5·0 mm, on total, cytosolic and mitochondrial creatine kinase activities from skeletal and cardiac muscle of 30-day-old Wistar rats. We also tested the effects of various antioxidants on the effects elicited by DGA. Results, We first verified that total creatine kinase (CK) activity from homogenates was significantly inhibited by DGA (22,24% inhibition) in skeletal and cardiac muscle, and that this activity was approximately threefold higher in skeletal muscle than in cardiac muscle. We also observed that CK activities from mitochondrial (Mi-CK) and cytosolic (Cy-CK) preparations from skeletal muscle and cardiac muscle were also inhibited (12,35% inhibition) by DGA at concentrations as low as 0·25 mm, with the effect being more pronounced in cardiac muscle preparations. Finally, we verified that the DGA-inhibitory effect was fully prevented by preincubation of the homogenates with reduced glutathione and cysteine, suggesting that this effect is possibly mediated by modification of essential thiol groups of the enzyme. Furthermore, ,-tocopherol, melatonin and the inhibitor of nitric oxide synthase L-NAME were unable to prevent this effect, indicating that the most common reactive oxygen and nitrogen species were not involved in the inhibition of CK provoked by DGA. Conclusion, Considering the importance of creatine kinase activity for cellular energy homeostasis, our results suggest that inhibition of this enzyme by increased levels of DGA might be an important mechanism involved in the myopathy and cardiomyopathy of patients affected by DHGA. [source] Effects of Temporal Application Parameters on Lesion Dimensions During Transvenous Catheter CryoablationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2 2005HUNG-FAT TSE M.D. Background: Transvenous catheter cryoablation is a novel technique for treating cardiac arrhythmias. However, the relative importance of temporal application parameters on lesion dimension and clinical efficacy has not been studied. Methods and Results: We investigated the effects of (1) application duration: single 2.5 (2.5 × 1) versus single 5 versus double 2.5 (2.5 × 2) versus double 5 (5 × 2) minutes, (2) number of freeze,thaw cycles: single versus double, and (3) electrode contact area: horizontal versus vertical orientation, on the lesion diameter and depth during catheter cryoablation (10F, 6.5-mm tip-electrode, CryoCorÔ, San Diego) in a thigh muscle preparation. A total of 175 lesions (horizontal = 90, vertical = 85) were created in thigh muscle preparations on 10 swine. The lesion diameter and depth were significantly greater using 2.5 × 2 and 5 × 2 application modes as compared with 2.5 × 1 applications (P < 0.05). Horizontal tip-electrode orientation produced larger lesion diameter (P < 0.05), but not lesion depth as compared with vertical orientation. Multivariate analysis demonstrated that both tip-electrode orientation and duration of freeze >2.5 minutes were independent predictors for lesion diameter (P < 0.001). However, only duration of freeze >2.5 minutes was an independent predictor for lesion depth (P < 0.001). Conclusions: The dimensions of lesions created by catheter cryoablation are affected by mode of cryoablation application and electrode orientation. Increasing the duration of application, employing multiple freeze,thaw cycles at shorter cycle durations, and orienting the catheter to enhance/increase tissue contact can create a larger lesion. [source] Spatial insulin signalling in isolated skeletal muscle preparationsJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 5 2010Peter Sogaard Abstract During in vitro incubation in the absence or presence of insulin, glycogen depletion occurs in the inner core of the muscle specimen, concomitant with increased staining of hypoxia-induced-factor-1-alpha and caspase-3, markers of hypoxia and apoptosis, respectively. The aim of this study was to determine whether insulin is able to diffuse across the entire muscle specimen in sufficient amounts to activate signalling cascades to promote glucose uptake and glycogenesis within isolated mouse skeletal muscle. Phosphoprotein multiplex assay on lysates from muscle preparation was performed to detect phosphorylation of insulin-receptor on Tyr1146, Akt on Ser473 and glycogen-synthases-kinase-3 on Ser21/Ser9. To address the spatial resolution of insulin signalling, immunohistochemistry studies on cryosections were performed. Our results provide evidence to suggest that during the in vitro incubation, insulin sufficiently diffuses into the centre of tubular mouse muscles to promote phosphorylation of these signalling events. Interestingly, increased insulin signalling was observed in the core of the incubated muscle specimens, correlating with the location of oxidative fibres. In conclusion, insulin action was not restricted due to insufficient diffusion of the hormone during in vitro incubation in either extensor digitorum longus or soleus muscles from mouse under the specific experimental settings employed in this study. Hence, we suggest that the glycogen depleted core as earlier observed is not due to insufficient insulin action. J. Cell. Biochem. 109: 943,949, 2010. © 2010 Wiley-Liss, Inc. [source] Postnatal downregulation of inhibitory neuromuscular transmission to the longitudinal muscle of the guinea pig ileumNEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009X. Bian Abstract, Neuromuscular transmission is crucial for normal gut motility but little is known about its postnatal maturation. This study investigated excitatory/inhibitory neuromuscular transmission in vitro using ileal nerve-muscle preparations made from neonatal (,48 h postnatal) and adult (,4 months postnatal) guinea pigs. In tissues from neonates and adults, nicotine (0.3,30 ,mol L,1) contracted longitudinal muscle preparations in a tetrodotoxin (TTX) (0.3 ,mol L,1)-sensitive manner. The muscarinic receptor antagonist, scopolamine (1 ,mol L,1), reduced substantially nicotine-induced contractions in neonatal tissues but not adult tissues. In the presence of N, -nitro- l -arginine (NLA, 100 ,mol L,1) to block nitric oxide (NO) mediated inhibitory neuromuscular transmission, scopolamine-resistant nicotine-induced contractions were revealed in neonatal tissues. NLA enhanced the nicotine-induced contractions in neonatal but not in adult tissues. Electrical field stimulation (20 V; 0.3 ms; 5,25 Hz, scopolamine 1 ,mol L,1 present) caused NLA and TTX-sensitive longitudinal muscle relaxations. Frequency,response curves in neonatal tissues were left-shifted compared with those obtained in adult tissues. Immunohistochemical studies revealed that NO synthase (NOS)-immunoreactivity (ir) was present in nerve fibres supplying the longitudinal muscle in neonatal and adult tissues. However, quantitative studies demonstrated that fluorescence intensity of NOS-ir nerve fibres was higher in neonatal than adult tissues. Nerve fibres containing substance P were abundant in longitudinal muscle in adult but not in neonatal tissues. Inhibitory neuromuscular transmission is relatively more effective in the neonatal guinea pig small intestine. Delayed maturation of excitatory motor pathways might contribute to paediatric motility disturbances. [source] Pharmacological studies on siculine syrup.PHYTOTHERAPY RESEARCH, Issue 2 2009II: effects on smooth, cardiovascular muscle preparations, skeletal Abstract Earlier pharmacological screening showed that siculine syrup (a traditional herbal remedy purported to be useful in the prevention and treatment of sickle cell pain , crises, due to sickle cell anaemia , SCA) had antisickling and analgesic activities as well as antimicrobial and diuretic effects. SCA is an important haemoglobinopathy in Africa and many other communities/countries worldwide, with relatively high morbidity and mortality. The present study was to determine the effects of the extract on various isolated muscle preparations , smooth, skeletal and cardiovascular. Siculine (4,20 µg/mL), like acetylcholine (40,400 µg/mL), contracted the isolated rat uterus concentration dependently. Similar effects were observed with the guinea-pig ileum and rabbit jejunum (2,20 µg/mL). In contrast to these effects, the direct (muscle) and indirect (nerve) stimulations of rat phrenic nerve,diaphragm were relaxed by siculine (4 and 8 µg/mL) and d -tubocurarine (0.8 µg/mL). Siculine also concentration-dependently decreased both the rate and force of contraction of guinea-pig atria and rabbit heart and also resulted in a fall in cat blood pressure in a manner similar to those of acetylcholine. The possible therapeutic and/or toxicological consequences of these effects including the hypotensive activity is noteworthy since siculine syrup is used by the local population for the prevention and treatment of sickle cell pain crises. Copyright © 2008 John Wiley & Sons, Ltd. [source] Smooth muscle contraction induced by Indigofera dendroides leaf extracts may involve calcium mobilization via potential sensitive channelsPHYTOTHERAPY RESEARCH, Issue 7 2003S. Amos Abstract The contractile effects of the aqueous extract of the leaves of Indigofera dendroides (ID) were studied on the gastrointestinal motility in mice and isolated smooth muscle preparations obtained from rats and guinea pigs. The contractile effects of 10,6 M acetylcholine, 80 mM KCl and 1.6 mg/ml ID were measured on the rat ileal smooth muscle exposed to calcium-free buffer or physiological solution, to determine the calcium pools mobilized by extract for activation of contraction. Acute toxicity test (LD50) was also carried out in mice. The result showed that ID (0.05,3.2 mg/ml) produced a concentration-dependent contraction of the guinea pig and rat ileum. These responses were not blocked by mepyramine (2.49 × 10,9 M), verapamil (8.14 × 10,9 M), or pirenzepine (4.7 × 10,7 M), but were blocked completely by atropine (2.92 × 10,9 M). A signi.cant increase in propulsion of gastrointestinal motility was observed. Acetylcholine, KCl and ID produced contractions in Ca2+ free media. The phasic components of the contractile responses to Ach as well as the tonic component of K+ and ID-induced contractions were relatively resistant to short periods of calcium-free exposure. Ach, K+ and ID still caused contractions in the presence of verapamil. The data revealed that ID-induced contractions were not mediated by histaminergic receptors, calcium channels, M1 muscarinic receptors. It also suggests that Ach mobilize Ca from some tightly bound or intracellular pool, whereas high K+ and ID may mobilize Ca from some superficial or loosely-bound pool. Copyright © 2003 John Wiley & Sons, Ltd. [source] Thirty-five years in bioelectromagnetics researchBIOELECTROMAGNETICS, Issue 1 2007C-K. Chou Abstract For 35 years, I have been involved in various bioelectromagnetics research projects including acute and long-term radiofrequency (RF) bioeffects studies, dosimetry, exposure systems, MRI safety, cancer studies involving hyperthermia and electrochemical treatment, development of RF exposure and measurement standards, and product compliance. My first study demonstrated that effects on isolated nerve and muscle preparations were due to thermal effects of RF exposure. The recording of cochlear microphonics in animals shows the mechanical nature of the microwave auditory effect. In 1992, we published the results of a large-scale lifetime study in which 100 rats were sham-exposed and 100 rats were exposed for 21 h/day for 25 months to a pulsed RF signal. In dosimetry studies, human models were employed as well as many animal species including mice, rats, rabbits, monkeys, and birds of many sizes. Cancer hyperthermia studies demonstrated that knowledge of temperature distribution was crucial for successful treatment. Research on electrochemical treatment of tumors with direct current involved cellular, animal, and clinical studies. Over the past few decades, there has been rather extensive investigation of the public health impact of RF exposure. In my opinion, future research in bioelectromagnetics should place greater emphasis on medical applications. Bioelectromagnetics © 2006 Wiley-Liss, Inc. [source] The mechanism for the contraction induced by leukotriene C4 in guinea-pig taenia coliBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2001Satoshi Ieiri The mechanism underlying the LTC4 -induced contraction of guinea-pig taenia coli was determined using the simultaneous measurements of [Ca2+]i and force in whole muscle preparations. Additional experiments were performed in receptor coupled permeabilized preparation. For comparison purposes, the contraction which was induced by a typical G-protein mediated agonist, carbachol was also characterized. LTC4 induced a contraction in the guinea-pig taenia coli in a concentration-dependent manner. The maximal response was obtained at 100 nM and the EC50 value was 5.4±1.9 nM. Both LTC4 and carbachol induced increases in [Ca2+]i and force. The maximum force induced by 100 nM LTC4 was significantly smaller than that induced by 10 ,M carbachol, although an increase in [Ca2+]i produced by both agonists was similar. In the permeabilized preparations, carbachol, but not LTC4, induced an additional force development at a fixed Ca2+ concentration. LTC4 induced no increase in [Ca2+]i and force in the Ca2+ -free solution, while carbachol induced transient increases in both [Ca2+]i and force in a Ca2+ -free solution. Both diltiazem and SK&F 96365 significantly inhibited the LTC4, and carbachol-induced increases in [Ca2+]i and force in normal PSS. The inhibitory pattern of [Ca2+]i by these drugs was also similar. We thus conclude that LTC4 induces the contraction of the guinea-pig taenia coli mainly through Ca2+ influx via both the diltiazem-sensitive and SK&F 96365-sensitive Ca2+ channels, without affecting either the Ca2+ -sensitivity or the intracellular Ca2+ release. These results indicated that the mechanism underlying the LTC4 -induced contraction differs greatly from that for conventional G-protein mediated agonists, such as carbachol. British Journal of Pharmacology (2001) 133, 529,538; doi:10.1038/sj.bjp.0704122 [source] In vitro neuromuscular activity of snake venomsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2002Wayne C Hodgson Summary 1.,Snake venoms consist of a multitude of pharmacologically active components used for the capture of prey. Neurotoxins are particularly important in this regard, producing paralysis of skeletal muscles. These neurotoxins can be classified according to their site of action (i.e. pre- or post-synaptic). 2.,Presynaptic neurotoxins, which display varying phospholipase A2 activities, have been identified in the venoms of the four major families of venomous snakes (i.e. Crotalidae, Elapidae, Hydrophiidae and Viperidae). The blockade of transmission produced by these toxins is usually characterized by a triphasic effect on acetylcholine release. Considerable work has been directed at identifying the binding site(s) on the presynaptic nerve terminal for these toxins, although their mechanism of action remains unclear. 3.,Post-synaptic neurotoxins are antagonists of the nicotinic receptor on the skeletal muscle. Depending on their sequence, post-synaptic toxins are subdivided into short- and long-chain toxins. These toxins display different binding kinetics and different affinity for subtypes of nicotinic receptors. Post-synaptic neurotoxins have only been identified in venoms from the families Elapidae and Hydrophiidae. 4.,Due to the high cost of developing new antivenoms and the reluctance of many companies to engage in this area of research, new methodologies are required to test the efficacy of existing antivenoms to ensure their optimal use. While chicken eggs have proven useful for the examination of haemorrhagic venoms, this procedure is not suited to venoms that primarily display neurotoxic activity. The chick biventer cervicis muscle has proven useful for this procedure, enabling the rapid screening of antivenoms against a range of venoms. 5.,Historically, the lethality of snake venoms has been based on murine LD50 studies. Due to ethical reasons, these studies are being superseded by in vitro studies. Instead, the time taken to produce 90% inhibition of nerve-mediated twitches (i.e. t90) in skeletal muscle preparations can be determined. However, these two procedures result in different rank orders because they are measuring two different parameters. While murine LD50 determinations are based on ,quantity', t90 values are based on how ,quick' a venom acts. Therefore, knowledge of both parameters is still desirable. 6.,In vitro neuromuscular preparations have proven to be invaluable tools in the examination of snake venoms and isolated neurotoxins. They will continue to play a role in further elucidating the mechanism of action of these highly potent toxins. Further study of these toxins may provide more highly specific research tools or lead compounds for pharmaceutical agents. [source] Rapid loss of motor nerve terminals following hypoxia,reperfusion injury occurs via mechanisms distinct from classic Wallerian degenerationJOURNAL OF ANATOMY, Issue 6 2008Becki Baxter Abstract Motor nerve terminals are known to be vulnerable to a wide range of pathological stimuli. To further characterize this vulnerability, we have developed a novel model system to examine the response of mouse motor nerve terminals in ex vivo nerve/muscle preparations to 2 h hypoxia followed by 2 h reperfusion. This insult induced a rapid loss of neurofilament and synaptic vesicle protein immunoreactivity at pre-synaptic motor nerve terminals but did not appear to affect post-synaptic endplates or muscle fibres. The severity of nerve terminal loss was dependent on the age of the mouse and muscle type: in 8,12-week-old mice the predominantly fast-twitch lumbrical muscles showed an 82.5% loss, whereas the predominantly slow-twitch muscles transversus abdominis and triangularis sterni showed a 57.8% and 27.2% loss, respectively. This was contrasted with a > 97% loss in the predominantly slow-twitch muscles from 5,6-week-old mice. We have also demonstrated that nerve terminal loss occurs by a mechanism distinct from Wallerian degeneration, as the slow Wallerian degeneration (Wlds) gene did not modify the extent of nerve terminal pathology. Together, these data show that our new model of hypoxia,reperfusion injury is robust and repeatable, that it induces rapid, quantitative changes in motor nerve terminals and that it can be used to further examine the mechanisms regulating nerve terminal vulnerability in response to hypoxia,reperfusion injury. [source] | |||||||||||||