Gorio A, Hurlbut W P, Ceccarelli B
J Cell Biol. 1978 Sep;78(3):716-33. doi: 10.1083/jcb.78.3.716.
We have studied the effects of 25 mM potassium, electrical stimulation of the phrenic nerve, and crude black widow spider venom on the ultrastructure, electrophysiology, and acetylcholine (ACh) contents of mouse diaphragms. About 65% of the ACh in diaphragms is contained in a depletable store in the nerve terminals. The rest of the ACh is contained in a nondepletable store that may correspond to the store that remains in denervated muscles and includes, in addition, ACh in the intramuscular branches of the phrenic nerve. About 4% of the ACh released from the depletable store at rest is secreted as quanta and may come from the vesicles, while 96% is secreted in a nonquantized form and comes from an extravesicular pool. The size of the extravesicular pool is uncertain: it could be less than 10%, or as great as 50%, of the depletable store. K causes a highly (but perhaps not perfectly) selective increase in the rate of quantal secretion so that quanta account for about 50% of the total ACh released from K-treated diaphragms. K, or electrical stimulation of the phrenic nerve, depletes both the vesicular and extravesicular pools of ACh when hemicholinium no. 3 (HC-3) is present. However, most of the vesicles are retained under these conditions so that the diaphragms are able to increase slightly their rates of release of ACh when K is added. Venom depletes the terminals of their vesicles and abolishes the release of quanta of ACh. It depletes the vesicular pool of ACh (since it depletes the vesicles), but may only partially deplete the extravesicular pool (since it reduces resting release only 10--40%). The rate of release of ACh from the residual extravesicular pool does not increase when 25 mM K is added. Although we cannot exclude the possibility that stimulation may double the rate of release of ACh from the extravesicular pool, our results are compatible with the idea that the ACh released by stimulation comes mainly from the vesicles and that, when synthesis is inhibited by HC-3, ACh may be exchanged between the extravesicular pool and recycled vesicles.
我们研究了25 mM钾、膈神经电刺激以及粗制黑寡妇蜘蛛毒液对小鼠膈肌超微结构、电生理学和乙酰胆碱（ACh）含量的影响。膈肌中约65%的ACh存在于神经末梢的可耗尽储存库中。其余的ACh存在于不可耗尽储存库中，这可能与去神经肌肉中残留的储存库相对应，此外还包括膈神经肌内分支中的ACh。静息时从可耗尽储存库释放的ACh中约4%以量子形式分泌，可能来自囊泡，而96%以非量子化形式分泌，来自囊泡外池。囊泡外池的大小不确定：它可能小于可耗尽储存库的10%，也可能高达50%。钾会导致量子分泌速率高度（但可能并非完美）选择性增加，使得量子约占钾处理膈肌释放的总ACh的50%。当存在三号半胱氨酸（HC - 3）时，钾或膈神经电刺激会耗尽ACh的囊泡池和囊泡外池。然而，在这些条件下大多数囊泡会保留下来，因此当加入钾时，膈肌能够略微增加其ACh释放速率。毒液会耗尽神经末梢的囊泡并消除ACh量子的释放。它会耗尽ACh的囊泡池（因为它会耗尽囊泡），但可能只会部分耗尽囊泡外池（因为它只会将静息释放降低10 - 40%）。当加入25 mM钾时，残留囊泡外池中ACh 的释放速率不会增加。虽然我们不能排除刺激可能使ACh从囊泡外池的释放速率加倍的可能性，但我们的结果与以下观点一致：刺激释放的ACh主要来自囊泡，并且当合成被HC - 3抑制时，ACh可能在囊泡外池和再循环囊泡之间进行交换。
