Ulus I H, Wurtman R J, Mauron C, Blusztajn J K
Department of Pharmacology, Uludag University Medical School, Bursa, Turkey.
Brain Res. 1989 Apr 10;484(1-2):217-27. doi: 10.1016/0006-8993(89)90364-8.
This study examined the possibility that membrane phospholipids might be a source of choline used for acetylcholine (ACh) synthesis. Slices of rat striatum or cerebellum were superfused with a choline-free or choline-containing (10, 20 or 40 microM) physiological solution with eserine, for alternating 20 min periods of rest or electrical stimulation. Superfusion media were assayed for choline and ACh, and slice samples taken before and after stimulation were assayed for choline, ACh, various phospholipids, protein and DNA. The striatal slices were able to sustain the stimulation-induced release of ACh, releasing a total of about 3 times their initial ACh contents during the 8 periods of stimulation and rest. During these 8 cycles, 885 pmol/micrograms DNA free choline was released from the slices into the medium, an amount about 45-fold higher than the initial or final free choline levels in the slices. Although repeated stimulation of the striatal slices failed to affect tissue levels of free choline or of ACh, this treatment did cause significant, dose-related (i.e., number of stimulation periods) stoichiometric decreases in tissue levels of phosphatidylcholine (PC) and of the other major phospholipids; tissue protein levels also declined significantly. Addition of exogenous choline to the superfusion medium produced dose-related increases in resting and evoked ACh release. The choline also fully protected the striatal slices from phospholipid depletion for as many as 6 stimulation periods. Cerebellar slices liberated large amounts of free choline into the medium but did not release measurable quantities of ACh; their phospholipid and protein levels did not decline with electrical stimulation. These data show that membrane phospholipids constitute a reservoir of free choline that can be used for ACh synthesis. When free choline is in short supply, ACh synthesis and release are sustained at the expense of this reservoir. The consequent reduction in membrane PC apparently is associated with a depletion of cellular membrane. The use of free choline by cholinergic neurons for two purposes, the syntheses of both ACh and membrane phospholipids, may thus impart vulnerability to them in situations where the supply of free choline is less than that needed for acetylation.
本研究探讨了膜磷脂可能是用于乙酰胆碱（ACh）合成的胆碱来源这一可能性。将大鼠纹状体或小脑切片用含或不含胆碱（10、20或40微摩尔）并添加毒扁豆碱的生理溶液进行灌流，交替进行20分钟的休息或电刺激。对灌流介质进行胆碱和ACh测定，对刺激前后采集的切片样本进行胆碱、ACh、各种磷脂、蛋白质和DNA测定。纹状体切片能够维持刺激诱导的ACh释放，在8个刺激和休息周期内共释放约3倍于其初始ACh含量的ACh。在这8个周期中，885皮摩尔/微克DNA的游离胆碱从切片释放到介质中，这一量比切片中初始或最终的游离胆碱水平高约45倍。尽管反复刺激纹状体切片未能影响游离胆碱或ACh的组织水平，但这种处理确实导致磷脂酰胆碱（PC）和其他主要磷脂的组织水平出现显著的、剂量相关（即刺激周期数）的化学计量减少；组织蛋白水平也显著下降。向灌流介质中添加外源性胆碱会导致静息和诱发的ACh释放出现剂量相关的增加。胆碱还能在多达6个刺激周期内充分保护纹状体切片免受磷脂消耗。小脑切片向介质中释放大量游离胆碱，但不释放可测量量的ACh；其磷脂和蛋白质水平不会因电刺激而下降。这些数据表明，膜磷脂构成了可用于ACh合成的游离胆碱储备。当游离胆碱供应短缺时，ACh的合成和释放以该储备为代价得以维持。随之而来的膜PC减少显然与细胞膜的消耗有关。胆碱能神经元将游离胆碱用于ACh和膜磷脂两种合成目的，因此在游离胆碱供应少于乙酰化所需量的情况下，可能使它们易受影响。
