Amplitude Of Miniature Endplate Potentials Research Articles

Characterization of neuromuscular synapse function abnormalities in multiple Duchenne muscular dystrophy mouse models.

Duchenne muscular dystrophy (DMD) is an X-linked myopathy caused by dystrophin deficiency. Dystrophin is present intracellularly at the sarcolemma, connecting actin to the dystrophin-associated glycoprotein complex. Interestingly, it is enriched postsynaptically at the neuromuscular junction (NMJ), but its synaptic function is largely unknown. Utrophin, a dystrophin homologue, is also concentrated at the NMJ, and upregulated in DMD. It is possible that the absence of dystrophin at NMJs in DMD causes neuromuscular transmission defects that aggravate muscle weakness. We studied NMJ function in mdx mice (lacking dystrophin) and wild type mice. In addition, mdx/utrn(+/-) and mdx/utrn(-/-) mice (lacking utrophin) were used to investigate influences of utrophin levels. The three Duchenne mouse models showed muscle weakness when comparatively tested invivo, with mdx/utrn(-/-) mice being weakest. Ex vivo muscle contraction and electrophysiological studies showed a reduced safety factor of neuromuscular transmission in all models. NMJs had ~40% smaller miniature endplate potential amplitudes compared with wild type, indicating postsynaptic sensitivity loss for the neurotransmitter acetylcholine. However, nerve stimulation-evoked endplate potential amplitudes were unchanged. Consequently, quantal content (i.e. the number of acetylcholine quanta released per nerve impulse) was considerably increased. Such a homeostatic compensatory increase in neurotransmitter release is also found at NMJs in myasthenia gravis, where autoantibodies reduce acetylcholine receptors. However, high-rate nerve stimulation induced exaggerated endplate potential rundown. Study of NMJ morphology showed that fragmentation of acetylcholine receptor clusters occurred in all models, being most severe in mdx/utrn(-/-) mice. Overall, we showed mild 'myasthenia-like' neuromuscular synaptic dysfunction in several Duchenne mouse models, which possibly affects muscle weakness and degeneration.

Changes in structure and function of diaphragm neuromuscular junctions from BACHD mouse model for Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder characterized by a progressive decline of motor and cognitive functions. It is caused by a polyglutamine expansion in the huntingtin (htt) protein, which then leads to neurodegeneration that span both the central and peripheral nervous system. Previous works have shown that htt interacts with several proteins from the neurotransmitter release machinery causing synaptic dysfunction. In this work, we looked for alterations in diaphragm neuromuscular junctions (NMJs) from 3 to 4 months old BACHD mouse model for HD. This model represents a new and robust in vivo paradigm for studying the pathogenesis of HD. For optical analysis, NMJs were stained with FM1-43fx and α-bungarotoxin to visualize both pre and postsynaptic elements, respectively. Confocal microscopy optical analysis showed a decrease in the number of synaptic elements and fluorescence intensity in NMJs from BACHD diaphragms compared to WT. We next analyzed presynaptic activity and we observed that synaptic vesicle exocytosis was impaired in NMJs from BACHD diaphragms. Ultrastructural analysis revealed significant changes in the form and sizes of the synaptic vesicles in BACHD diaphragm NMJs that could contribute to impaired exocytosis. Additionally, electrophysiology recordings revealed a decrease in the amplitude of miniature endplate potentials (MEPPs) from BACHD diaphragm NMJs. Our data suggest a dysfunction in BACHD diaphragm NMJs that might occur in other muscles and may aggravate the motor defects seen in HD. These results may contribute to a better understanding of peripheral cholinergic dysfunction in this neurodegenerative disease.

Action of NMDA receptors agonists on amplitude of miniature endplate potentials in PRiMA and ColQ genes knockout mice

Action of NMDA receptors agonists on amplitude of miniature endplate potentials in PRiMA and ColQ genes knockout mice

Postsynaptic Potentiation in Mouse Motor Synapses Induced by ATP Accumulation in Synaptic Cleft.

In mouse motor synapses, a non-selective purinoceptor antagonist suramin increased the quantum content of endplate potentials (EPP) without changing the time course of synaptic potentials. An ectonucleotidase inhibitor ARL 67156 had no effect on the amplitude and quantum content of EPP and miniature endplate potentials (mEPP) evoked by single stimuli, but significantly prolonged their duration. Long-term high-frequency stimulation of the nerve in the presence of ARL 67156 persistently increased the amplitude and duration of EPP during the train of impulses, but did not change their quantum content. ATP-γ-S, a non-hydrolyzed ATP analogue, significantly increased the amplitudes and prolonged the rising and falling phases of EPP and mEPP. The ATP-induced postsynaptic potentiation in neuromuscular transmission can result from the increase in ATP content and its longer presence in the synaptic cleft.

Mechanism of neuromuscular dysfunction in Krabbe disease.

The atrophy of skeletal muscles in patients with Krabbe disease is a major debilitating manifestation that worsens their quality of life and limits the clinical efficacy of current therapies. The pathogenic mechanism triggering muscle wasting is unknown. This study examined structural, functional, and metabolic changes conducive to muscle degeneration in Krabbe disease using the murine (twitcher mouse) and canine [globoid cell leukodystrophy (GLD) dog] models. Muscle degeneration, denervation, neuromuscular [neuromuscular junction (NMJ)] abnormalities, and axonal death were investigated using the reporter transgenic twitcher-Thy1.1-yellow fluorescent protein mouse. We found that mutant muscles had significant numbers of smaller-sized muscle fibers, without signs of regeneration. Muscle growth was slow and weak in twitcher mice, with decreased maximum force. The NMJ had significant levels of activated caspase-3 but limited denervation. Mutant NMJ showed reduced surface areas and lower volumes of presynaptic terminals, with depressed nerve control, increased miniature endplate potential (MEPP) amplitude, decreased MEPP frequency, and increased rise and decay rate constants. Twitcher and GLD dog muscles had significant capacity to store psychosine, the neurotoxin that accumulates in Krabbe disease. Mechanistically, muscle defects involved the inactivation of the Akt pathway and activation of the proteasome pathway. Our work indicates that muscular dysfunction in Krabbe disease is compounded by a pathogenic mechanism involving at least the failure of NMJ function, activation of proteosome degradation, and a reduction of the Akt pathway. Akt, which is key for muscle function, may constitute a novel target to complement in therapies for Krabbe disease.

Effect of 50% enantiomeric excess bupivacaine mixture combined with pancuronium on neuromuscular transmission in rat phrenic nerve-diaphragm preparation; a pilot study.

Background and Aims:Local anaesthetics are drugs that are widely used in clinical practice. However, the effects of these drugs on the neuromuscular junction and their influence on the blockade produced by non-depolarising neuromuscular blocking drugs are still under investigation. The aim of this study was to evaluate, in vitro, the influence of a 50% enantiomeric excess bupivacaine mixture on neuromuscular transmission and neuromuscular block produced by pancuronium.Methods:Rats were distributed into three groups (n = 5) according to the drug studied namely, 50% enantiomeric excess bupivacaine mixture (5 μg/mL); pancuronium (2 μg/mL); 50% enantiomeric excess bupivacaine mixture + pancuronium. The following parameters were evaluated: (1) Effects of a 50% enantiomeric excess bupivacaine mixture on membrane potential (MP) and miniature endplate potentials (MEPPs); (2) amplitude of diaphragmatic response before and 60 min after the addition of a 50% enantiomeric excess bupivacaine mixture; the degree of neuromuscular block with pancuronium and pancuronium combined with a 50% enantiomeric excess bupivacaine mixture.Results:A 50% enantiomeric excess bupivacaine mixture did not alter the amplitude of muscle response (MP) but decreased the frequency and amplitude of MEPP. The block produced by pancuronium was potentiated by a 50% enantiomeric excess bupivacaine mixture.Conclusion:A 50% enantiomeric excess bupivacaine mixture used alone did not affect neuromuscular transmission, but potentiated the neuromuscular block produced by pancuronium. No action was shown on the muscle fibre, and alterations on MEPPs demonstrated a presynaptic action.

Guidelines for pre-clinical animal and cellular models of MuSK-myasthenia gravis

Muscle-specific tyrosine kinase (MuSK) autoantibodies are the hallmark of a form of myasthenia gravis (MG) that can challenge the neurologist and the experimentalist. The clinical disease can be difficult to treat effectively. MuSK autoantibodies affect the neuromuscular junction in several ways. When added to muscle cells in culture, MuSK antibodies disperse acetylcholine receptor clusters. Experimental animals actively immunized with MuSK develop MuSK autoantibodies and muscle weakness. Weakness is associated with reduced postsynaptic acetylcholine receptor numbers, reduced amplitudes of miniature endplate potentials and endplate potentials, and failure of neuromuscular transmission. Similar impairments have been found in mice injected with IgG from MG patients positive for MuSK autoantibody (MuSK-MG). The active and passive models have begun to reveal the mechanisms by which MuSK antibodies disrupt synaptic function at the neuromuscular junction, and should be valuable in developing therapies for MuSK-MG. However, translation into new and improved treatments for patients requires procedures that are not too cumbersome but suitable for examining different aspects of MuSK function and the effects of potential therapies. Study design, conduct and analysis should be carefully considered and transparently reported. Here we review what has been learnt from animal and culture models of MuSK-MG, and offer guidelines for experimental design and conduct of studies, including sample size determination, randomization, outcome parameters and precautions for objective data analysis. These principles may also be relevant to the increasing number of other antibody-mediated diseases that are now recognized.

A role for solute carrier family 10 member 4, or vesicular aminergic-associated transporter, in structural remodelling and transmitter release at the mouse neuromuscular junction.

The solute carrier and presynaptic vesicle protein solute carrier family 10 member 4, or vesicular aminergic-associated transporter (VAAT), was recently proven to have a modulatory role in central cholinergic signalling. It is currently unknown whether VAAT also affects peripheral cholinergic synapses. Here we demonstrated a regulatory role for the presynaptic vesicle protein VAAT in neuromuscular junction (NMJ) development and function. NMJs lacking VAAT had fewer branch points, whereas endplates showed an increased number of islands. Whereas the amplitude of spontaneous miniature endplate potentials in VAAT-deficient NMJs was decreased, the amplitude of evoked endplate potentials and the size of the readily releasable pool of vesicles were both increased. Moreover, VAAT-deficient NMJs displayed aberrant short-term synaptic plasticity with enhanced synaptic depression in response to high-frequency stimulation. Finally, the transcript levels of cholinergic receptor subunits in VAAT-deficient muscles were increased, indicating a compensatory postsynaptic sensitization. Our results suggested that VAAT modulates NMJ transmission efficiency and, as such, may represent a novel target for treatment of disorders affecting motor neurons.

LRP4 is critical for neuromuscular junction maintenance.

The neuromuscular junction (NMJ) is a synapse between motor neurons and skeletal muscle fibers, and is critical for control of muscle contraction. Its formation requires neuronal agrin that acts by binding to LRP4 to stimulate MuSK. Mutations have been identified in agrin, MuSK, and LRP4 in patients with congenital myasthenic syndrome, and patients with myasthenia gravis develop antibodies against agrin, LRP4, and MuSK. However, it remains unclear whether the agrin signaling pathway is critical for NMJ maintenance because null mutation of any of the three genes is perinatal lethal. In this study, we generated imKO mice, a mutant strain whose LRP4 gene can be deleted in muscles by doxycycline (Dox) treatment. Ablation of the LRP4 gene in adult muscle enabled studies of its role in NMJ maintenance. We demonstrate that Dox treatment of P30 mice reduced muscle strength and compound muscle action potentials. AChR clusters became fragmented with diminished junctional folds and synaptic vesicles. The amplitude and frequency of miniature endplate potentials were reduced, indicating impaired neuromuscular transmission and providing cellular mechanisms of adult LRP4 deficiency. We showed that LRP4 ablation led to the loss of synaptic agrin and the 90 kDa fragments, which occurred ahead of other prejunctional and postjunctional components, suggesting that LRP4 may regulate the stability of synaptic agrin. These observations demonstrate that LRP4 is essential for maintaining the structural and functional integrity of the NMJ and that loss of muscle LRP4 in adulthood alone is sufficient to cause myasthenic symptoms.

Reduced Expression of the Vesicular Acetylcholine Transporter and Neurotransmitter Content Affects Synaptic Vesicle Distribution and Shape in Mouse Neuromuscular Junction

In vertebrates, nerve muscle communication is mediated by the release of the neurotransmitter acetylcholine packed inside synaptic vesicles by a specific vesicular acetylcholine transporter (VAChT). Here we used a mouse model (VAChT KDHOM) with 70% reduction in the expression of VAChT to investigate the morphological and functional consequences of a decreased acetylcholine uptake and release in neuromuscular synapses. Upon hypertonic stimulation, VAChT KDHOM mice presented a reduction in the amplitude and frequency of miniature endplate potentials, FM 1–43 staining intensity, total number of synaptic vesicles and altered distribution of vesicles within the synaptic terminal. In contrast, under electrical stimulation or no stimulation, VAChT KDHOM neuromuscular junctions did not differ from WT on total number of vesicles but showed altered distribution. Additionally, motor nerve terminals in VAChT KDHOM exhibited small and flattened synaptic vesicles similar to that observed in WT mice treated with vesamicol that blocks acetylcholine uptake. Based on these results, we propose that decreased VAChT levels affect synaptic vesicle biogenesis and distribution whereas a lower ACh content affects vesicles shape.

Evidence of presynaptic and postsynaptic action of local anesthetics in rats

To assess the probable actions of ropivacaine, 50% enantiomeric excess bupivacaine mixture (S75-R25) and levobupivacaine on neuromuscular transmission in vitro. Thirty rats were distributed into groups (n=5) according to the drug used: ropivacaine, bupivacaine (S75-R25) and levobupivacaine. The concentration used for the three local anesthetics (LA) was 5 µg.mL. (-1)The following parameters were evaluated: 1) LA effects on membrane potential (MP) and miniature end plate potential (MEPP). A chick biventer cervicis preparation was also used to evaluate LA effects on the contracture response to acetylcholine. LA did not alter MP values and decreased the frequency and amplitude of MEPP. In a chick biventer cervicis preparation, bupivacaine (S75-R25) and levobupivacaine decreased the contracture response to acetylcholine with statistical significance, in comparison to ropivacaine. In the concentrations used, levobupivacaine and bupivacaine (S75-R25) exhibited presynaptic and postsynaptic actions evidenced by alterations in miniature end plate potentials and contracture response to acetylcholine. Ropivacaine only had a presynaptic action.

Neuromuscular blocking activity of pinnatoxins E, F and G

Pinnatoxins are produced by dinoflagellates and belong to the cyclic imine family of toxins. They are fast-acting and highly toxic when administered in vivo in rodent bioassays, causing death by respiratory depression within minutes. Studies have revealed that some cyclic imine toxins cause their toxicity by antagonizing both muscle type and heteromeric and homomeric neuronal nicotinic acetylcholine receptors (nAChRs). Pinnatoxins E, F and G all display potent toxicity in in vivo bioassays, with symptoms of toxicity similar to other cyclic imine toxins. However, very little work has been done on the mechanism of action of these pinnatoxin isomers. Thus the aim of the current study was to investigate the rank order of potency and mechanism of action of pinnatoxins E, F and G. The effects of pinnatoxin E, F and G on in vitro rat hemidiaphragm preparations were investigated using twitch tension and electrophysiological techniques to determine the effects of these toxins on cholinergic transmission at the neuromuscular junction. Pinnatoxins E, F and G all produced concentration-dependent reductions in the nerve evoked twitch response of the rat hemidiaphragm, with IC50 values ranging from 11 to 53 nM and a rank order of potency of F > G > E. Only complete washout of pinnatoxin E was evident, with pinnatoxins F and G displaying slow and incomplete washout profiles. Pinnatoxins F and G also reduced the amplitudes of spontaneous miniature endplate potentials and evoked endplate potentials at the neuromuscular junction, without affecting miniature endplate potential frequency or the resting membrane potential of the muscle fibres. These results show that pinnatoxins E, F and G are all potent neuromuscular blocking agents and cause toxicity by acting as antagonists at muscle type nicotinic acetylcholine receptors.

Etomidate evokes synaptic vesicle exocytosis without increasing miniature endplate potentials frequency at the mice neuromuscular junction

Etomidate is an intravenous anesthetic used during anesthesia induction. This agent induces spontaneous movements, especially myoclonus after its administration suggesting a putative primary effect at the central nervous system or the periphery. Therefore, the aim of this study was to investigate the presynaptic and postsynaptic effects of etomidate at the mouse neuromuscular junction (NMJ). Diaphragm nerve muscle preparations were isolated and stained with the styryl dye FM1-43, a fluorescent tool that tracks synaptic vesicles exo-endocytosis that are key steps for neurotransmission. We observed that etomidate induced synaptic vesicle exocytosis in a dose-dependent fashion, an effect that was independent of voltage-gated Na+ channels. By contrast, etomidate-evoked exocytosis was dependent on extracellular Ca2+ because its effect was abolished in Ca2+-free medium and also inhibited by omega-Agatoxin IVA (30 and 200nM) suggesting the participation of P/Q-subtype Ca2+ channels. Interestingly, even though etomidate induced synaptic vesicle exocytosis, we did not observe any significant difference in the frequency and amplitude of miniature end-plate potentials (MEPPs) in the presence of the anesthetic. We therefore investigated whether etomidate could act on nicotinic acetylcholine receptors labeled with α-bungarotoxin-Alexa 594 and we observed less fluorescence in preparations exposed to the anesthetic. In conclusion, our results suggest that etomidate exerts a presynaptic effect at the NMJ inducing synaptic vesicle exocytosis, likely through the activation of P-subtype voltage gated Ca2+ channels without interfering with MEPPs frequency. The present data contribute to a better understanding about the effect of etomidate at the neuromuscular synapse and may help to explain some clinical effects of this agent.

Complexin facilitates exocytosis and synchronizes vesicle release in two secretory model systems

Complexins (Cplxs) are small, SNARE-associated proteins believed to regulate fast, calcium-triggered exocytosis. However, studies have pointed to either an inhibitory and/or facilitatory role in exocytosis, and the role of Cplxs in synchronizing exocytosis is relatively unexplored. Here, we compare the function of two types of complexin, Cplx 1 and 2, in two model systems of calcium-dependent exocytosis. In mouse neuromuscular junctions (NMJs), we find that lack of Cplx 1 significantly reduces and desynchronizes calcium-triggered synaptic transmission; furthermore, high-frequency stimulation elicits synaptic facilitation, instead of normal synaptic depression, and the degree of facilitation is highly sensitive to the amount of cytoplasmic calcium buffering. In Cplx 2-null adrenal chromaffin cells, we also find decreased and desynchronized evoked release, and identify a significant reduction in the vesicle pool close to the calcium channels (immediately releasable pool, IRP). Viral transduction with either Cplx 1 or 2 rescues both the size of the evoked response and the synchronicity of release, and it restores the IRP size. Our findings in two model systems are mutually compatible and indicate a role of Cplx 1 and 2 in facilitating vesicle priming, and also lead to the new hypothesis that Cplxs may synchronize vesicle release by promoting coupling between secretory vesicles and calcium channels.

Exome sequencing detection of two untranslated GFPT1 mutations in a family with limb‐girdle myasthenia

The term 'limb-girdle myasthenia' (LGM) was first used to describe three siblings with proximal limb weakness without oculobulbar involvement, but with EMG decrement and responsiveness to anticholinesterase medication. We report here that exome sequencing in the proband of this family revealed several sequence variations in genes linked to proximal limb weakness. However, the only mutations that cosegregated with disease were an intronic IVS7-8A>G mutation and the previously reported 3'-UTR c.*22C>A mutation in GFPT1, a gene linked to LGM. A minigene assay showed that IVS7-8A>G activates an alternative splice acceptor that results in retention of the last seven nucleotides of intron 7 and a frameshift leading to a termination codon 13 nucleotides downstream from the new splice site. An anconeus muscle biopsy revealed mild reduction of the axon terminal size and postsynaptic fold simplification. The amplitudes of miniature endplate potentials and quantal release were also diminished. The DNA of the mildly affected father of the proband showed only the intronic mutation along with sequence variations in other genes potentially relevant to LGM. Thus, this study performed in the family originally described with LGM showed two GFPT1 untranslated mutations, which may cause disease by reducing GFPT1 expression and ultimately impairing protein glycosylation.

Effects and Mechanisms of Action of Nitric Oxide on Transmitter Release in Mouse Motor Nerve Terminals

We examined the mechanisms of NO action on transmitter release in neuromuscular preparations of the mouse diaphragm muscle using a standard microelectrode technique. A donor of NO (SNAP, 100 μM) and a substrate for NO synthesis (L-arginine, 100 μM) reduced the evoked transmitter release from motor nerve endings. At the same time, SNAP did not change the frequency and amplitude of miniature end-plate potentials, while an inhibitor of NO synthase, L-NAME, exerted no effect on evoked and spontaneous transmitter release. Inhibition of soluble guanylate cyclase by ODQ (2.5 μM) abolished the effect of NO on the evoked transmitter release, while the elevation of cGMP-level by its membranepenetrating analog 8BrcGMP did not prevent such effect. The elevation of intracellular concentration of cAMP by 100 μM of its analog 8(4CPT) cAMP or inhibition of phosphodiesterase (PDE) by the action of 100 μM IBMX eliminated NO effects on transmitter release. It is concluded that NO activates soluble guanylate cyclase and intensifies the cGMP synthesis. Activation of the PDE II via an increase in the cGMP level with consequent reduction of the level of intracellular cAMP and decrease in the activity of PKA reduced transmitter release from mouse motor nerve ending.

The non-competitive acetylcholinesterase inhibitor APS12-2 is a potent antagonist of skeletal muscle nicotinic acetylcholine receptors

APS12-2, a non-competitive acetylcholinesterase inhibitor, is one of the synthetic analogs of polymeric alkylpyridinium salts (poly-APS) isolated from the marine sponge Reniera sarai. In the present work the effects of APS12-2 were studied on isolated mouse phrenic nerve–hemidiaphragm muscle preparations, using twitch tension measurements and electrophysiological recordings. APS12-2 in a concentration-dependent manner blocked nerve-evoked isometric muscle contraction (IC50=0.74μM), without affecting directly-elicited twitch tension up to 2.72μM. The compound (0.007–3.40μM) decreased the amplitude of miniature endplate potentials until a complete block by concentrations higher than 0.68μM, without affecting their frequency. Full size endplate potentials, recorded after blocking voltage-gated muscle sodium channels, were inhibited by APS12-2 in a concentration-dependent manner (IC50=0.36μM) without significant change in the resting membrane potential of the muscle fibers up to 3.40μM. The compound also blocked acetylcholine-evoked inward currents in Xenopus oocytes in which Torpedo (α12β1γδ) muscle-type nicotinic acetylcholine receptors (nAChRs) have been incorporated (IC50=0.0005μM), indicating a higher affinity of the compound for Torpedo (α12β1γδ) than for the mouse (α12β1γε) nAChR. Our data show for the first time that APS12-2 blocks neuromuscular transmission by a non-depolarizing mechanism through an action on postsynaptic nAChRs of the skeletal neuromuscular junction.

Presence and Pathogenic Relevance of Antibodies to Clustered Acetylcholine Receptor in Ocular and Generalized Myasthenia Gravis

Clustered acetylcholine receptor antibodies (clustered AChR-Abs) have been detected in a proportion of patients with previously "seronegative" (SN) generalized myasthenia gravis (GMG), but their presence in patients with ocular MG (OMG) and their pathogenicity in vivo are unknown. To test the presence of clustered AChR-Abs and their pathophysiologic properties in patients with SNMG. Screening and diagnostic tests. Regional specialist myasthenia center and clinical laboratory. Serum samples from 16 patients with SN and OMG were tested for binding to clustered AChRs. Results from 28 further SN patients (14 OMG) were correlated with their single fiber electromyography values. Presence, complement-fixation capacity, correlation with neurophysiologic changes, and in vivo pathogenicity of clustered AChR-Abs. Up to 50% of patients with previous SN-OMG had complement-fixing IgG1 clustered AChR-Abs. IgG binding (n = 28) and complement deposition (n = 21) each correlated with the mean consecutive difference (jitter) on single-fiber electromyography. Injection of purified IgG from 2 patients with clustered AChR-Abs into wild-type or complement regulator-deficient mice reduced miniature end plate potential amplitudes to an extent similar to that found with AChR-Abs, and complement was deposited at the end plates. A trend was noted toward an increase in the number of packets of acetylcholine released (quantal content). A proportion of patients with SN-GMG or OMG have clustered AChR-Abs that correlate with their electrophysiologic features. Clustered AChR-Abs can passively transfer disease to mice, demonstrating their pathogenicity, and the mechanisms seem similar to those of patients with typical AChR-Abs.

Role of Stored Calcium in the Regulation of Neurotransmitter Quantum Size

Release of stored calcium ions during activation of ryanodine receptors with ryanodine or caffeine elevates the mean amplitude of spontaneous miniature end-plate potentials. Blockade of these receptors with selective antagonists abolishes this effect. Preliminary loading of the motor nerve terminals with intracellular calcium buffer EGTA-AM, but not with BAPTA-AM, also completely prevented the ryanodine-induced increment of miniature end-plate potential amplitude probably induced by the release of stored calcium. Vesamicol, a selective blocker of acetylcholine transport into vesicles, prevented the ryanodine-induced increment of the mean amplitude of miniature end-plate potentials. This increment was 2-fold more pronounced after preliminary blockade of protein kinase C with chelerythrine and was completely abolished by blockade of protein kinase A with H-89.

Effect of 2-Nitropropane on Chemical Neurotransmission, Spontaneous and Evoked, in the Sartorius Muscle of the Frog

n this project we studied the effect of 2-nitropropane in spontaneous and evoked chemical neurotransmission, using as a model the frog neuromuscular junction, in vitro. The experiments were carried out in the sciatic nerve- sartorius muscle preparation. Our results show that neurotransmission was inhibited, manifesting as a decrease in the amplitude and instantaneous frequency of miniature end-plate potentials and the reduction of end-plate potentials amplitude of the neuromuscular junction, evoked by nerve stimulation. Because 2-nitropropane showed inhibitory effects at peripheral level, we recommend that in work environments where there is exposure to organic solvents, neurological clinical examinations must be performed to detect abnormalities or neurological damage the earlie