Spontaneous acetylcholine release in mammalian neuromuscular junctions

1997 ◽  
Vol 273 (6) ◽  
pp. C1835-C1841 ◽  
Author(s):  
Adriana Losavio ◽  
S. Muchnik
Keyword(s):  
Neuromuscular Junction ◽  
Acetylcholine Release ◽  
Neuromuscular Junctions ◽  
The Other ◽  
Nerve Terminals ◽  
Transmitter Secretion ◽  
Other Hand ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Lower Effect

Spontaneous secretion of the neurotransmitter acetylcholine in mammalian neuromuscular synapsis depends on the Ca2+ content of nerve terminals. The Ca2+ electrochemical gradient favors the entry of this cation. We investigated the possible involvement of three voltage-dependent Ca2+ channels (VDCC) (L-, N-, and P/Q-types) on spontaneous transmitter release at the rat neuromuscular junction. Miniature end-plate potential (MEPP) frequency was clearly reduced by 5 μM nifedipine, a blocker of the L-type VDCC, and to a lesser extent by the N-type VDCC blocker, ω-conotoxin GVIA (ω-CgTx, 5 μM). On the other hand, nifedipine and ω-CgTx had no effect on K+-induced transmitter secretion. ω-Agatoxin IVA (100 nM), a P/Q-type VDCC blocker, prevents acetylcholine release induced by K+ depolarization but failed to affect MEPP frequency in basal conditions. These results suggest that in the mammalian neuromuscular junction Ca2+ enters nerve terminals through at least three different channels, two of them (L- and N-types) mainly related to spontaneous acetylcholine release and the other (P/Q-type) mostly involved in depolarization-induced neurotransmitter release. Ca2+-binding molecule-related spontaneous release apparently binds Ca2+ very rapidly and would probably be located very close to Ca2+ channels, since the fast Ca2+ chelator (BAPTA-AM) significantly reduced MEPP frequency, whereas EGTA-AM, exhibiting slower kinetics, had a lower effect. The increase in MEPP frequency induced by exposing the preparation to hypertonic solutions was affected by neither external Ca2+concentration nor L-, N-, and P/Q-type VDCC blockers, indicating that extracellular Ca2+ is not necessary to produce hyperosmotic neurosecretion. On the other hand, MEPP frequency was diminished by BAPTA-AM and EGTA-AM to the same extent, supporting the view that hypertonic response is promoted by “bulk” intracellular Ca2+concentration increases.

scholarly journals Adrenoceptors Modulate Cholinergic Synaptic Transmission at the Neuromuscular Junction

2021 ◽  
Vol 22 (9) ◽  
pp. 4611
Author(s):  
Ellya Bukharaeva ◽  
Venera Khuzakhmetova ◽  
Svetlana Dmitrieva ◽  
Andrei Tsentsevitsky
Keyword(s):  
Neuromuscular Junction ◽  
Neurodegenerative Diseases ◽  
Acetylcholine Receptors ◽  
Molecular Mechanisms ◽  
Acetylcholine Release ◽  
Neuromuscular Junctions ◽  
Motor Nerve ◽  
Nerve Terminals ◽  
Adrenergic Agents ◽  
Cholinergic Synaptic Transmission

Adrenoceptor activators and blockers are widely used clinically for the treatment of cardiovascular and pulmonary disorders. More recently, adrenergic agents have also been used to treat neurodegenerative diseases. Recent studies indicate a location of sympathetic varicosities in close proximity to neuromuscular junctions. The pressing question is whether there could be any effects of endo- or exogenous catecholamines on cholinergic neuromuscular transmission. It was shown that the pharmacological stimulation of adrenoceptors, as well as sympathectomy, can affect both acetylcholine release from motor nerve terminals and the functioning of postsynaptic acetylcholine receptors. In this review, we discuss the recent data regarding the effects of adrenergic drugs on neurotransmission at the neuromuscular junction. The elucidation of the molecular mechanisms by which the clinically relevant adrenomimetics and adrenoblockers regulate quantal acetylcholine release from the presynaptic nerve terminals and postsynaptic sensitivity may help in the design of highly effective and well-tolerated sympathomimetics for treating a number of neurodegenerative diseases accompanied by synaptic defects.

The Dogfish Neuromuscular Junction: Dual Innervation of Vertebrate Striated Muscle Fibres?

1972 ◽  
Vol 10 (3) ◽  
pp. 657-665
Author(s):  
Q. BONE
Keyword(s):  
Neuromuscular Junction ◽  
Nerve Terminal ◽  
Striated Muscle ◽  
Dense Core ◽  
The Other ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Nerve Fibres ◽  
Different Types ◽  
Motor End Plate

In the myotomal muscles of the dogfish, Scyliorhinu canicula, there are 2 major types of fibre. The red fibres at the periphery of the myotome receive a distributed en grappe pattern of innervation. There are subjunctional folds at these endings, and the nerve terminals contain vesicles around 50 nm in diameter. In contrast to this, the white twitch fibres of the myotome are innervated focally, by 2 nerve fibres passing to the same motor end-plate. These 2 fibres contain vesicles of different types. One type of nerve terminal contains vesicles around 50 nm in diameter; these terminals resemble those upon the red fibres. The other contains vesicles up to 100 nm in diameter, frequently possessing a dense core. It is suggested that the white twitch fibres of dogfish are innervated by 2 separate axons, possibly containing different transmitter substances.

Intraterminal Ca2+ and Spontaneous Transmitter Release at the Frog Neuromuscular Junction

2001 ◽  
Vol 85 (1) ◽  
pp. 287-294 ◽  
Author(s):  
J. K. Angleson ◽  
W. J. Betz
Keyword(s):  
Neuromuscular Junction ◽  
Phorbol Ester ◽  
Intracellular Recording ◽  
Transmitter Release ◽  
The Other ◽  
Nerve Terminals ◽  
Frog Neuromuscular Junction ◽  
Tetraacetic Acid ◽  
Ratiometric Imaging ◽  
The Relationship

We investigated the relationship between intraterminal Ca2+concentration ([Ca2+]i) and the frequency of miniature end plate potentials (MEPPs) at the frog neuromuscular junction by use of ratiometric imaging of fura-2-loaded nerve terminals and intracellular recording of MEPPs. Elevation of extracellular [KCl] over the range of 2–20 mM resulted in increases in [Ca2+]i and MEPP frequency. Loading terminals with the fast and slow Ca2+-buffers bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid-acetoxymethyl (BAPTA-AM) and EGTA-AM resulted in equivalent reductions in the KCl-dependent increases in MEPP frequency. The [Ca2+]i dependence of MEPP frequency determined by elevation of [Ca2+]i due to application of 0.1–10 μM ionomycin was similar to that determined when [Ca2+]i was raised by increasing extracellular KCl. Measurements in 10 mM extracellular KCl revealed that application of the phorbol ester phorbol 12 myristate 13-acetetate (PMA) caused an increase in MEPP frequency while the inactive analogue, 4α-PMA, did not. PMA application also caused an increase in [Ca2+]i. The relationship between [Ca2+]i and MEPP frequency in PMA was the same as was determined by the other methods of raising [Ca2+]i. Under all conditions tested, our data revealed a low [Ca2+]i threshold for activation of transmitter release and are consistent with a K d for [Ca2+]i on the order of 1 μM.

Endurance exercise modulates neuromuscular junction of C57BL/6NNia aging mice

1997 ◽  
Vol 83 (1) ◽  
pp. 59-66 ◽  
Author(s):  
Mohamed A. Fahim
Keyword(s):  
Neuromuscular Junction ◽  
Endurance Exercise ◽  
Neuromuscular Junctions ◽  
Safety Margin ◽  
Gluteus Maximus ◽  
Nerve Terminals ◽  
Quantal Content ◽  
Age Related ◽  
Endplate Potentials ◽  
Old Mice

Fahim, Mohamed A. Endurance exercise modulates neuromuscular junction of C57BL/6NNia aging mice. J. Appl. Physiol. 83(1): 59–66, 1997.—The effect of age and endurance exercise on the physiology and morphology of neuromuscular junctions (NMJ) of gluteus maximus muscle was studied in C57BL/6NNia mice. Mice were exercised, starting at 7 or 25 mo of age, at 28 m/min for 60 min/day, 5 days/wk for 12 wk, on a rodent treadmill. Intracellular recordings of spontaneous miniature endplate potentials (MEPP) and the quantal content of endplate potentials (EPP) were recorded from NMJ of 10- and 28-mo-old control and exercised mice. Endurance exercise resulted in significant increases in MEPP amplitudes (23%), quantal content, and safety margin, and a significant decrease in MEPP frequency of young mice, with no change in resting membrane potential or membrane capacitance. Three months of endurance exercise resulted in an increase in MEPP frequency (41%) and decreases in MEPP amplitudes (15%), quantal content, and safety margin of old mice. Endurance exercise resulted in significantly larger nerve terminals (24%) in young animals, suggesting functional adaptation. Nerve terminals in exercised 28-mo-old mice were smaller than in the corresponding control mice, an indication that exercise minimized age-related nerve terminal elaboration. It is concluded that the different physiological responses of young and old gluteus maximus muscles to endurance exercise parallel their morphological responses. This suggests that the mouse NMJ undergoes a process of physiological and morphological remodeling during aging, and such plasticity could be modulated differently by endurance exercise.

Calmodulin interactions with IQ peptides from voltage-dependent calcium channels

2005 ◽  
Vol 288 (3) ◽  
pp. C669-C676 ◽  
Author(s):  
D. J. Black ◽  
D. Brent Halling ◽  
David V. Mandich ◽  
Steen E. Pedersen ◽  
Ruth A. Altschuld ◽  
...  
Keyword(s):  
Calcium Channels ◽  
The Other ◽  
Multiple Functions ◽  
Iq Motif ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Voltage Dependent Calcium Channels ◽  
Cam Regulation

Calmodulin (CaM) functions as a Ca2+ sensor for inactivation and, in some cases, facilitation of a variety of voltage-dependent Ca2+ channels. A crucial determinant for CaM binding to these channels is the IQ motif in the COOH-terminal tail of the channel-forming subunit. The binding of CaM to IQ peptides from Lc-, P/Q-, and R-type, but not N-type, voltage-dependent Ca2+ channels increases the Ca2+ affinity of both lobes of CaM, producing similar N- and C-lobe Ca2+ affinities. Ca2+ associates with and dissociates from the N-lobe much more rapidly than the C-lobe when CaM is bound to the IQ peptides. Compared with the other IQ peptides, CaM-bound Lc-IQ has the highest Ca2+ affinity and the most rapid rates of Ca2+ association at both lobes, which is likely to make Ca2+ binding to CaM, bound to this channel, less sensitive than other channels to intracellular Ca2+ buffers. These kinetic differences in Ca2+ binding to the lobes of CaM when bound to the different IQ motifs may explain both the ability of CaM to perform multiple functions in these channels and the differences in CaM regulation of the different voltage-dependent Ca2+ channels.

Different VAMP/Synaptobrevin Complexes for Spontaneous and Evoked Transmitter Release at the Crayfish Neuromuscular Junction

1998 ◽  
Vol 80 (6) ◽  
pp. 3233-3246 ◽  
Author(s):  
Shao-Ying Hua ◽  
Dorota A. Raciborska ◽  
William S. Trimble ◽  
Milton P. Charlton
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Neurotransmitter Release ◽  
Action Potentials ◽  
Neuromuscular Junctions ◽  
Spontaneous Release ◽  
Intracellular Ca ◽  
Crayfish Neuromuscular Junction ◽  
Evoked Transmitter Release

Hua, Shao-Ying, Dorota A. Raciborska, William S. Trimble, and Milton P. Charlton. Different VAMP/synaptobrevin complexes for spontaneous and evoked transmitter release at the crayfish neuromuscular junction. J. Neurophysiol. 80: 3233–3246, 1998. Although vesicle-associated membrane protein (VAMP/synaptobrevin) is essential for evoked neurotransmitter release, its role in spontaneous transmitter release remains uncertain. For instance, many studies show that tetanus toxin (TeNT), which cleaves VAMP, blocks evoked transmitter release but leaves some spontaneous transmitter release. We used recombinant tetanus and botulinum neurotoxin catalytic light chains (TeNT-LC, BoNT/B-LC, and BoNT/D-LC) to examine the role of VAMP in spontaneous transmitter release at neuromuscular junctions (nmj) of crayfish. Injection of TeNT-LC into presynaptic axons removed most of the VAMP immunoreactivity and blocked evoked transmitter release without affecting nerve action potentials or Ca2+ influx. The frequency of spontaneous transmitter release was little affected by the TeNT-LC when the evoked transmitter release had been blocked by >95%. The spontaneous transmitter release left after TeNT-LC treatment was insensitive to increases in intracellular Ca2+. BoNT/B-LC, which cleaves VAMP at the same site as TeNT-LC but uses a different binding site, also blocked evoked release but had minimal effect on spontaneous release. However, BoNT/D-LC, which cleaves VAMP at a different site from the other two toxins but binds to the same position on VAMP as TeNT, blocked both evoked and spontaneous transmitter release at similar rates. The data indicate that different VAMP complexes are employed for evoked and spontaneous transmitter release; the VAMP used in spontaneous release is not readily cleaved by TeNT or BoNT/B. Because the exocytosis that occurs after the action of TeNT cannot be increased by increased intracellular Ca2+, the final steps in neurotransmitter release are Ca2+ independent.

scholarly journals Lycopene depresses glutamate release through inhibition of voltage-dependent Ca2+ entry and protein kinase C in rat cerebrocortical nerve terminals

2018 ◽  
Vol 96 (5) ◽  
pp. 479-484 ◽  
Author(s):  
Cheng-Wei Lu ◽  
Chi-Feng Hung ◽  
Wei-Horng Jean ◽  
Tzu-Yu Lin ◽  
Shu-Kuei Huang ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Glutamate Release ◽  
Inhibitory Effect ◽  
Nerve Terminals ◽  
Protein Kinase C Inhibitors ◽  
Kinase C ◽  
Protein Kinase C Activity ◽  
Voltage Dependent ◽  
Intracellular Ca

Lycopene is a natural dietary carotenoid that was reported to exhibit a neuroprotective profile. Considering that excitotoxicity and cell death induced by glutamate are involved in many brain disorders, the effect of lycopene on glutamate release in rat cerebrocortical nerve terminals and the possible mechanism involved in such effect was investigated. We observed here that lycopene inhibited 4-aminopyridine (4-AP)-evoked glutamate release and intrasynaptosomal Ca2+ concentration elevation. The inhibitory effect of lycopene on 4-AP-evoked glutamate release was markedly reduced in the presence of the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but was insensitive to the intracellular Ca2+-release inhibitors dantrolene and CGP37157. Furthermore, in the presence of the protein kinase C inhibitors GF109203X and Go6976, the action of lycopene on evoked glutamate release was prevented. These results are the first to suggest that lycopene inhibits glutamate release from rat cortical synaptosomes by suppressing presynaptic Ca2+ entry and protein kinase C activity.

scholarly journals Fine Gating Properties of Channels Responsible for Persistent Sodium Current Generation in Entorhinal Cortex Neurons

2002 ◽  
Vol 120 (6) ◽  
pp. 855-873 ◽  
Author(s):  
Jacopo Magistretti ◽  
Angel Alonso
Keyword(s):  
Entorhinal Cortex ◽  
Voltage Dependence ◽  
Burst Duration ◽  
The Other ◽  
Na Channel ◽  
Kinetic Properties ◽  
Channel Activity ◽  
Other Hand ◽  
Voltage Dependent ◽  
The Mean

The gating properties of channels responsible for the generation of persistent Na+ current (INaP) in entorhinal cortex layer II principal neurons were investigated by performing cell-attached, patch-clamp experiments in acutely isolated cells. Voltage-gated Na+-channel activity was routinely elicited by applying 500-ms depolarizing test pulses positive to −60 mV from a holding potential of −100 mV. The channel activity underlying INaP consisted of prolonged and frequently delayed bursts during which repetitive openings were separated by short closings. The mean duration of openings within bursts was strongly voltage dependent, and increased by e times per every ∼12 mV of depolarization. On the other hand, intraburst closed times showed no major voltage dependence. The mean duration of burst events was also relatively voltage insensitive. The analysis of burst-duration frequency distribution returned two major, relatively voltage-independent time constants of ∼28 and ∼190 ms. The probability of burst openings to occur also appeared largely voltage independent. Because of the above “persistent” Na+-channel properties, the voltage dependence of the conductance underlying whole-cell INaP turned out to be largely the consequence of the pronounced voltage dependence of intraburst open times. On the other hand, some kinetic properties of the macroscopic INaP, and in particular the fast and intermediate INaP-decay components observed during step depolarizations, were found to largely reflect mean burst duration of the underlying channel openings. A further INaP decay process, namely slow inactivation, was paralleled instead by a progressive increase of interburst closed times during the application of long-lasting (i.e., 20 s) depolarizing pulses. In addition, long-lasting depolarizations also promoted a channel gating modality characterized by shorter burst durations than normally seen using 500-ms test pulses, with a predominant burst-duration time constant of ∼5–6 ms. The above data, therefore, provide a detailed picture of the single-channel bases of INaP voltage-dependent and kinetic properties in entorhinal cortex layer II neurons.

Na+/Ca2+ Exchanger in GABAergic Presynaptic Boutons of Rat Central Neurons

2002 ◽  
Vol 87 (4) ◽  
pp. 1694-1702 ◽  
Author(s):  
Atsushi Doi ◽  
Yasuhiro Kakazu ◽  
Norio Akaike
Keyword(s):  
External Solution ◽  
Cyclopiazonic Acid ◽  
Transient Increase ◽  
Nerve Terminals ◽  
Central Neurons ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Presynaptic Boutons ◽  
Terminal Excitability

Rat Meynert neurons were acutely isolated using a dissociation technique that maintains functional GABAergic presynaptic boutons. Miniature inhibitory postsynaptic currents (mIPSCs) were recorded under voltage-clamp conditions using whole cell patch-clamp recordings. Using the frequency of mIPSCs as a measure of presynaptic terminal excitability, the existence of a Na+/Ca2+ exchanger (NCX) in these GABAergic nerve terminals was clearly demonstrated. Both the frequency and the amplitude of mIPSCs were unaffected by replacement of extracellular Na2+. However, in this Na+-free external solution, ouabain could now induce a transient increase of mIPSCs frequency, which was not inhibited by adding Cd2+ or cyclopiazonic acid but was inhibited by removing external Ca2+. This indicates that this transient potentiation was dependent on external Ca2+, but that this Ca2+influx was not via voltage-dependent Ca2+channels. KB-R7943, an inhibitor of NCX, at a concentration of 3 × 10−6 M, reduced this transient increase of mIPSCs frequency without affecting mIPSCs amplitude and the response to exogenous GABA. These results demonstrate the existence of NCX in these GABAergic nerve terminals. In zero external Na+, ouabain causes an accumulation of intraterminal Na+ and a resultant influx of Ca2+ through the reversed mode operation of NCX. However, under more physiological conditions, NCX may also operate in a forward mode and serve to maintain low intracellular [Ca2+] in nerve terminals.

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