Synaptic vesicle recruitment for release explored by Monte Carlo simulation at the crayfish neuromuscular junction

1999 ◽  
Vol 77 (9) ◽  
pp. 634-650 ◽  
Author(s):  
K M Kennedy ◽  
S T Piper ◽  
H L Atwood
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Neuromuscular Junction ◽  
Calcium Channels ◽  
Calcium Channel ◽  
Synaptic Vesicle ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Single Channel ◽  
Separation Distance

Neurotransmission at chemically transmitting synapses requires calcium-mediated fusion of synaptic vesicles with the presynaptic membrane. Utilizing ultrastructural information available for the crustacean excitatory neuromuscular junction, we developed a model that employs the Monte Carlo simulation technique to follow the entry and movement of Ca2+ ions at a presynaptic active zone, where synaptic vesicles are preferentially docked for release. The model includes interaction of Ca2+ with an intracellular buffer, and variable separation between calcium channels and vesicle-associated Ca2+-binding targets that react with Ca2+ to trigger vesicle fusion. The end point for vesicle recruitment for release was binding of four Ca2+ ions to the target controlling release. The results of the modeling experiments showed that intracellular structures that interfere with Ca2+ diffusion (in particular synaptic vesicles) influence recruitment or priming of vesicles for release. Vesicular recruitment is strongly influenced by the separation distance between an opened calcium channel and the target controlling release, and by the concentration and binding properties of the intracellular buffers, as in previous models. When a single opened calcium channel is very close to the target, a single synaptic vesicle can be recruited. However, many of the single-channel openings actuated by a nerve impulse are likely to be ineffective for release, although they contribute to the buildup of total intracellular Ca2+. Thus, the overall effectiveness of single calcium channels in causing vesicles to undergo exocytosis is likely quite low.Key words: synapse, Monte Carlo simulation, synaptic vesicle, active zone, vesicle recruitment, crayfish, calcium, calcium buffer.

scholarly journals Transmitter release is evoked with low probability predominately by calcium flux through single channel openings at the frog neuromuscular junction

2015 ◽  
Vol 113 (7) ◽  
pp. 2480-2489 ◽  
Author(s):  
Fujun Luo ◽  
Markus Dittrich ◽  
Soyoun Cho ◽  
Joel R. Stiles ◽  
Stephen D. Meriney
Keyword(s):  
Neuromuscular Junction ◽  
Calcium Channels ◽  
Calcium Channel ◽  
Calcium Ions ◽  
Transmitter Release ◽  
Synaptic Vesicles ◽  
Vesicle Fusion ◽  
Frog Neuromuscular Junction ◽  
Low Probability ◽  
Presynaptic Calcium

The quantitative relationship between presynaptic calcium influx and transmitter release critically depends on the spatial coupling of presynaptic calcium channels to synaptic vesicles. When there is a close association between calcium channels and synaptic vesicles, the flux through a single open calcium channel may be sufficient to trigger transmitter release. With increasing spatial distance, however, a larger number of open calcium channels might be required to contribute sufficient calcium ions to trigger vesicle fusion. Here we used a combination of pharmacological calcium channel block, high-resolution calcium imaging, postsynaptic recording, and 3D Monte Carlo reaction-diffusion simulations in the adult frog neuromuscular junction, to show that release of individual synaptic vesicles is predominately triggered by calcium ions entering the nerve terminal through the nearest open calcium channel. Furthermore, calcium ion flux through this channel has a low probability of triggering synaptic vesicle fusion (∼6%), even when multiple channels open in a single active zone. These mechanisms work to control the rare triggering of vesicle fusion in the frog neuromuscular junction from each of the tens of thousands of individual release sites at this large model synapse.

scholarly journals Insulation of the conduction pathway of muscle transverse tubule calcium channels from the surface charge of bilayer phospholipid.

1986 ◽  
Vol 87 (6) ◽  
pp. 933-953 ◽  
Author(s):  
R Coronado ◽  
H Affolter
Keyword(s):  
Ionic Strength ◽  
Calcium Channels ◽  
Calcium Channel ◽  
Surface Charge ◽  
Single Channel ◽  
Small Surface ◽  
Bilayer Lipid ◽  
Sodium Conductance ◽  
Conduction Pathway ◽  
Lipid Surface

Functional calcium channels present in purified skeletal muscle transverse tubules were inserted into planar phospholipid bilayers composed of the neutral lipid phosphatidylethanolamine (PE), the negatively charged lipid phosphatidylserine (PS), and mixtures of both. The lengthening of the mean open time and stabilization of single channel fluctuations under constant holding potentials was accomplished by the use of the agonist Bay K8644. It was found that the barium current carried through the channel saturates as a function of the BaCl2 concentration at a maximum current of 0.6 pA (at a holding potential of 0 mV) and a half-saturation value of 40 mM. Under saturation, the slope conductance of the channel is 20 pS at voltages more negative than -50 mV and 13 pS at a holding potential of 0 mV. At barium concentrations above and below the half-saturation point, the open channel currents were independent of the bilayer mole fraction of PS from XPS = 0 (pure PE) to XPS = 1.0 (pure PS). It is shown that in the absence of barium, the calcium channel transports sodium or potassium ions (P Na/PK = 1.4) at saturating rates higher than those for barium alone. The sodium conductance in pure PE bilayers saturates as a function of NaCl concentration, following a curve that can be described as a rectangular hyperbola with a half-saturation value of 200 mM and a maximum conductance of 68 pS (slope conductance at a holding potential of 0 mV). In pure PS bilayers, the sodium conductance is about twice that measured in PE at concentrations below 100 mM NaCl. The maximum channel conductance at high ionic strength is unaffected by the lipid charge. This effect at low ionic strength was analyzed according to J. Bell and C. Miller (1984. Biophysical Journal. 45:279-287) and interpreted as if the conduction pathway of the calcium channel were separated from the bilayer lipid by approximately 20 A. This distance thereby effectively insulates the ion entry to the channel from the bulk of the bilayer lipid surface charge. Current vs. voltage curves measured in NaCl in pure PE and pure PS show that similarly small surface charge effects are present in both inward and outward currents. This suggests that the same conduction insulation is present at both ends of the calcium channel.

Depolarization-stimulated cholecystokinin secretion is mediated by L-type calcium channels in STC-1 cells

1996 ◽  
Vol 270 (2) ◽  
pp. G287-G290 ◽  
Author(s):  
A. W. Mangel ◽  
L. Scott ◽  
R. A. Liddle
Keyword(s):  
Calcium Channels ◽  
Calcium Channel ◽  
Calcium Channel Blocker ◽  
Channel Blocker ◽  
Single Channel ◽  
Bay K 8644 ◽  
Ic50 Value ◽  
Single Channel Currents ◽  
Dose Dependent ◽  
Cck Release

To examine the role of calcium channels in depolarization-activated cholecystokinin (CCK) release, studies were performed in an intestinal CCK-secreting cell line, STC-1. Blockade of potassium channels with barium chloride (5 mM) increased the release of CCK by 374.6 +/- 46.6% of control levels. Barium-induced secretion was inhibited by the L-type calcium-channel blocker, nicardipine. Nicardipine (10(-9)-10(-5) M) produced a dose-dependent inhibition in barium-stimulated secretion with a half-maximal inhibition (IC50) value of 0.1 microM. A second L-type calcium-channel blocker, diltiazem (10(-9)-10(-4) M), also inhibited barium-induced CCK secretion with an IC50 value of 5.1 microM. By contrast, the T-type calcium-channel blocker, nickel chloride (10(-7)-10(-8) M), failed to significantly inhibit barium-induced CCK secretion. To further evaluate a role for L-type calcium channels in the secretion of CCK, the effects of the L-type calcium channel opener, BAY K 8644, were examined. BAY K 8644 (10(-8)-10(-4) M) produced a dose-dependent stimulation in CCK release with a mean effective concentration value of 0.2 microM. Recordings of single-channel currents from inside-out membrane patches showed activation of calcium channels by BAY K 8644 (1 microM), with a primary channel conductance of 26.0 +/- 1.2 pS. It is concluded that inhibition of potassium channel activity depolarizes the plasma membrane, thereby activating L-type, but not T-type, calcium channels. The corresponding influx of calcium serves to trigger secretion of CCK.

Active zone assembly and synaptic release

2006 ◽  
Vol 34 (5) ◽  
pp. 939-941 ◽  
Author(s):  
R.J. Kittel ◽  
S. Hallermann ◽  
S. Thomsen ◽  
C. Wichmann ◽  
S.J. Sigrist ◽  
...  
Keyword(s):  
Calcium Channels ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Spatial Arrangement ◽  
Transmission Characteristics ◽  
Vesicle Release ◽  
Synaptic Release ◽  
Voltage Gated Calcium Channels ◽  
Presynaptic Calcium ◽  
Chemical Synapses

Neurotransmitter release at chemical synapses occurs when synaptic vesicles fuse to the presynaptic membrane at a specialized site termed the active zone. The depolarization-induced fusion is highly dependent on calcium ions, and, correspondingly, the transmission characteristics of synapses are thought to be influenced by the spatial arrangement of voltage-gated calcium channels with respect to vesicle release sites. Here, we review the involvement of the Drosophila Bruchpilot (BRP) protein in active zone assembly, a process that is required for the clustering of presynaptic calcium channels to ensure efficient vesicle release.

Neurotransmitter Release

2017 ◽  
Author(s):  
Peggy Mason
Keyword(s):  
Plasma Membrane ◽  
Synaptic Vesicle ◽  
Active Zone ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Synaptic Cleft ◽  
Fusion Pore ◽  
Synaptic Membrane ◽  
Specialized Region ◽  
Synaptic Vesicle Fusion

The biochemical and physiological processes of neurotransmitter release from an active zone, a specialized region of synaptic membrane, are examined. Synaptic vesicles containing neurotransmitters are docked at the active zone and then primed for release by SNARE complexes that bring them into extreme proximity to the plasma membrane. Entry of calcium ions through voltage-gated calcium channels triggers synaptic vesicle fusion with the synaptic terminal membrane and the consequent diffusion of neurotransmitter into the synaptic cleft. Release results when the fusion pore bridging the synaptic vesicle and plasma membrane widens and neurotransmitter from the inside of the synaptic vesicle diffuses into the synaptic cleft. Membrane from the active zone membrane is endocytosed, and synaptic vesicle proteins are then reassembled into recycled synaptic vesicles, allowing for more rounds of neurotransmitter release.

scholarly journals Synuclein Regulates Synaptic Vesicle Clustering and Docking at a Vertebrate Synapse

2021 ◽  
Vol 9 ◽  
Author(s):  
Kaitlyn E. Fouke ◽  
M. Elizabeth Wegman ◽  
Sarah A. Weber ◽  
Emily B. Brady ◽  
Cristina Román-Vendrell ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Significant Loss ◽  
Binding Partner ◽  
Reserve Pool ◽  
Associated Proteins ◽  
Dose Dependent ◽  
Total Membrane ◽  
Synapsin 1

Neurotransmission relies critically on the exocytotic release of neurotransmitters from small synaptic vesicles (SVs) at the active zone. Therefore, it is essential for neurons to maintain an adequate pool of SVs clustered at synapses in order to sustain efficient neurotransmission. It is well established that the phosphoprotein synapsin 1 regulates SV clustering at synapses. Here, we demonstrate that synuclein, another SV-associated protein and synapsin binding partner, also modulates SV clustering at a vertebrate synapse. When acutely introduced to unstimulated lamprey reticulospinal synapses, a pan-synuclein antibody raised against the N-terminal domain of α-synuclein induced a significant loss of SVs at the synapse. Both docked SVs and the distal reserve pool of SVs were depleted, resulting in a loss of total membrane at synapses. In contrast, antibodies against two other abundant SV-associated proteins, synaptic vesicle glycoprotein 2 (SV2) and vesicle-associated membrane protein (VAMP/synaptobrevin), had no effect on the size or distribution of SV clusters. Synuclein perturbation caused a dose-dependent reduction in the number of SVs at synapses. Interestingly, the large SV clusters appeared to disperse into smaller SV clusters, as well as individual SVs. Thus, synuclein regulates clustering of SVs at resting synapses, as well as docking of SVs at the active zone. These findings reveal new roles for synuclein at the synapse and provide critical insights into diseases associated with α-synuclein dysfunction, such as Parkinson’s disease.

scholarly journals Quantal Fluctuations in Central Mammalian Synapses: Functional Role of Vesicular Docking Sites

2017 ◽  
Vol 97 (4) ◽  
pp. 1403-1430 ◽  
Author(s):  
Camila Pulido ◽  
Alain Marty
Keyword(s):  
Neuromuscular Junction ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Site Occupancy ◽  
Physical Nature ◽  
Frog Neuromuscular Junction ◽  
Docking Site ◽  
Single Action ◽  
Docking Sites ◽  
Central Synapses

Quantal fluctuations are an integral part of synaptic signaling. At the frog neuromuscular junction, Bernard Katz proposed that quantal fluctuations originate at “reactive sites” where specific structures of the presynaptic membrane interact with synaptic vesicles. However, the physical nature of reactive sites has remained unclear, both at the frog neuromuscular junction and at central synapses. Many central synapses, called simple synapses, are small structures containing a single presynaptic active zone and a single postsynaptic density of receptors. Several lines of evidence indicate that simple synapses may release several synaptic vesicles in response to a single action potential. However, in some synapses at least, each release event activates a significant fraction of the postsynaptic receptors, giving rise to a sublinear relation between vesicular release and postsynaptic current. Partial receptor saturation as well as synaptic jitter gives to simple synapse signaling the appearance of a binary process. Recent investigations of simple synapses indicate that the number of released vesicles follows binomial statistics, with a maximum reflecting the number of docking sites present in the active zone. These results suggest that at central synapses, vesicular docking sites represent the reactive sites proposed by Katz. The macromolecular architecture and molecular composition of docking sites are presently investigated with novel combinations of techniques. It is proposed that variations in docking site numbers are central in defining intersynaptic variability and that docking site occupancy is a key parameter regulating short-term synaptic plasticity.

Synaptic Vesicle Distribution and Release at Rat Diaphragm Neuromuscular Junctions

2007 ◽  
Vol 98 (1) ◽  
pp. 478-487 ◽  
Author(s):  
Katharine L. Rowley ◽  
Carlos B. Mantilla ◽  
Leonid G. Ermilov ◽  
Gary C. Sieck
Keyword(s):  
Synaptic Vesicle ◽  
Phrenic Nerve ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Fiber Type ◽  
Repetitive Stimulation ◽  
Diaphragm Muscle ◽  
Type I ◽  
Fiber Types ◽  
Rat Diaphragm

Synaptic vesicle release at the neuromuscular junction (NMJ) is highly reliable and is vital to the success of synaptic transmission. We examined synaptic vesicle number, distribution, and release at individual type-identified rat diaphragm NMJ. Three-dimensional reconstructions of electron microscopy images were used to obtain novel measurements of active zone distribution and the number of docked synaptic vesicles. Diaphragm muscle-phrenic nerve preparations were used to perform electrophysiological measurements of the decline in quantal content (QC) during repetitive phrenic nerve stimulation. The number of synaptic vesicles available for release vastly exceeds those released with a single stimulus, thus reflecting a relatively low probability of release for individual docked vesicles and at each active zone. There are two components that describe the decline in QC resulting from repetitive stimulation: a rapid phase (<0.5 s) and a delayed phase (<2.5 s). Differences in the initial rapid decline in QC were evident across type-identified presynaptic terminals (fiber type classification based on myosin heavy chain composition). At terminals innervating type IIx and/or IIb fibers, the initial decline in QC during repetitive stimulation matched the predicted depletion of docked synaptic vesicles. In contrast, at terminals innervating type I or IIa fibers, a faster than predicted decline in QC with repetitive stimulation suggests that a decrease in the probability of release at these terminals plays a role in addition to depletion of docked vesicles. Differences in QC decline likely reflect fiber-type specific differences in activation history and correspond with well-described differences in neuromuscular transmission across muscle fiber types.

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