Carroll P T
Department of Pharmacology, Texas Tech University Health Sciences Center, Lubbock 79430, USA.
Brain Res. 1996 Jun 24;725(1):3-10. doi: 10.1016/0006-8993(96)00078-9.
Rat hippocampal minces were loaded with [acetyl 1-14C]acetylcholine ([14C]ACh) in the presence of the "poorly penetrating" acetylcholinesterase (EC 3.1.1.7; AChE) inhibitor echothiophate and the effect of high K+ depolarization determined on the subcellular storage and release of [14C]ACh and its metabolites. Results indicated that high K+ did not augment the release of [14C]ACh. Rather, it increased the release of [14C]acetate while simultaneously reducing the level of [14C]ACh in the cytosolic (S3) fraction. When the identical experiment was performed with paraoxon, a "penetrating" AChE inhibitor, high K+ still did not increase the release of [14C]ACh. However, paraoxon prevented the K(+)-induced loss of [14C]ACh from the cytosolic fraction as well as the K(+)-induced gain of [14C]acetate in the release medium. When minces were loaded with [14C]ACh in the presence of echothiophate and subsequently subjected to high K+ depolarization in the absence or presence of vesamicol (AH5183; (-)-trans-2-[4-phenylpiperidino] cyclohexanol), a drug which blocks the refilling of synaptic vesicles with ACh, the amount of endogenous ACh released was reduced approximately 50%. Conversely, the amount of [14C]ACh released was not reduced at all. These results suggest that cytosolic ACh is not directly transported into synaptic vesicles for release when hippocampal nerve terminals are depolarized. Rather, its hydrolysis is accelerated in response to depolarization. A working hypothesis explaining the importance of the depolarization-induced breakdown of cytosolic ACh to central ACh metabolism is presented.
在“穿透性差”的乙酰胆碱酯酶（EC 3.1.1.7；AChE）抑制剂碘磷定存在的情况下，将大鼠海马切碎组织用[乙酰基1-14C]乙酰胆碱（[14C]ACh）进行负载，并测定高钾去极化对[14C]ACh及其代谢产物的亚细胞储存和释放的影响。结果表明，高钾并没有增加[14C]ACh的释放。相反，它增加了[14C]乙酸盐的释放，同时降低了胞质（S3）组分中[14C]ACh的水平。当用对氧磷（一种“穿透性”AChE抑制剂）进行相同实验时，高钾仍然没有增加[14C]ACh的释放。然而，对氧磷阻止了钾离子诱导的[14C]ACh从胞质组分中的丢失以及释放介质中[14C]乙酸盐的钾离子诱导的增加。当切碎组织在碘磷定存在的情况下用[14C]ACh进行负载，随后在不存在或存在囊泡菌素（AH5183；（-）-反式-2-[4-苯基哌啶基]环己醇）（一种阻断ACh重新填充突触囊泡的药物）的情况下进行高钾去极化时，内源性ACh释放量减少了约50%。相反，[14C]ACh的释放量根本没有减少。这些结果表明，当海马神经末梢去极化时，胞质ACh不会直接转运到突触囊泡中进行释放。相反，其水解会因去极化而加速。本文提出了一个解释去极化诱导的胞质ACh分解对中枢ACh代谢重要性的工作假说。
