Vesicular hypothesis
Vesicles are site of neurotransmitter storage and release into synaptic cleft
Quantal release
Vesicular hypothesis requires that neurotransmitter be released in discrete packets corresponding to contents of one vesicle, synaptic vesicles of a particular type in neuron are about same size
Miniature end plate potentials (mepps)
Evidence for quantal release from frog neuromuscular junction
· Highly amplified intracellular recordings from muscles at neuromuscular junction
· Minute, spontaneous postsynaptic potentials, amplitude varies in 0.5 mV steps, suggesting release of discrete numbers of quanta
Mepps do not prove that full sized EPPs are quantal
· At neuromuscular junction estimated several hundred vesicles involved in EPP, small variation in size make it impossible to observe effects of adding one or two vesicles
Experiment demonstrating quantal nature of EPP
· Reduce number of quanta in EPP by partially blocking neurotransmitter release with high levels of extracellular Mg2+ (Mg2+ blocks Ca2+ channels)
· If Mg2+ levels are high, only a little neurotransmitter is released and release is quantal as shown above
· An estimated 200 quanta involved in normal neuromuscular junction EPP
Some synapses release smaller number of quanta, in some cases only 1
Mechanism of vesicular release
1) Mobilization of vesicles
· Vesicles bound to cytoskeleton, often actin filaments, and held firmly in place, must be freed for release
· Process requires Ca2+ influx
Storage pool anchored vesicles
Releasable pool vesicles attached to membrane and ready for release
· Vesicles that are mobilized are not the same ones as those released for given AP, delay between opening of Ca2+ channels and release of neurotransmitter only 0.1 to 0.2 msec, not enough time for cascade of biochemical events required to mobilize vesicle
Influx of Ca2+ has 2 distinct effects:
1. release of presynaptic vesicles already docked at membrane
2. mobilization of vesicles from storage pool to releasable pool by promoting docking with membrane, mechanism by which vesicle moves and docks not yet understood
vesicles mobilized in one event of synaptic transmission are released in subsequent event
泡是neurotransmitter存储的站点和synaptic裂缝的释放
Quantal释放
小囊的假设要求那neurotransmitter被释放在对一个泡的内容相应的离散的若干包中，神经原中的一种特殊的类型的synaptic泡是关于同样的大小的
缩影末端盘子潜力( mepps )
关于quantal释放的证据青蛙神经与肌的接合
· 高度扩大来自在神经与肌的接合的肌肉的intracellular录音
· 分钟，自发的postsynaptic潜力，振幅在0.5个mV步骤方面变化，建议释放离散的若干数字的总量
Mepps不证明如实物大EPP是quantal
· 在神经与肌的接合估计与EPP有关的几百个泡，大小的小的变体制定不可能观察增加一或者两个泡的结果
显示EPP的quantal性质的实验
· 通过部分地阻塞neurotransmitter释放减少EPP中的总量的数字高的水平的extracellular Mg2+ ( Mg2+阻塞Ca2+通道)
· 如果Mg2+水平高，仅仅小neurotransmitter被释放与释放在上面作为是quantal被显示的
· 与正常的神经与肌的接合EPP有关的估计的200个总量
一些触处发布总量的较小的数字，在某些情况中仅仅1
小囊的释放的机制
1)动员泡
· cytoskeleton的泡境界，经常actin细丝，和坚定地保持在原地，为了释放必须被释放
· 过程要求Ca2+流入
存储水塘抛锚泡
把水塘泡释放到膜附加和为释放作好准备
· 被动员的泡当那些释放的时，是同样的给AP，Ca2+通道的开始和neurotransmitter仅仅0.1到0.2 msec的释放之间的延迟并非足够，生物化学的事件的瀑布的时间要求动员泡
Ca2+的流入有2种明显的结果：
1.释放presynaptic泡已经在膜减少
2.动员泡存储水塘通过促进入船坞发布水塘膜，泡行动和船坞尚未理解的的机制
在synaptic传输的一个事件中被动员的泡被释放在后来的事件中
不好意思有些翻译不出来
