Farber S A, Savci V, Wei A, Slack B E, Wurtman R J
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA.
Brain Res. 1996 Jun 3;723(1-2):90-9. doi: 10.1016/0006-8993(96)00221-1.
The mechanism by which populations of brain cells regulate the flux of choline (Ch) into membrane or neurotransmitter biosynthesis was investigated using electrically stimulated superfused slices of rat corpus striatum. [Me-14C]Ch placed in the superfusion medium for 30 min during a 1-h stimulation period was incorporated into tissue [14C] phosphorylcholine (PCh) and [14C]phosphatidylcholine (PtdCh). Stimulation also caused a profound inhibition of PCh synthesis and a 10-fold increase in [14C]ACh release into the medium; it failed to affect tissue [14C]ACh levels. This effect was not explained by changes in ATP levels nor in the kinetic properties of Ch kinase (E.C. 2.7.1.32) or Ch acetyltransferase (ChAT) (E.C.2.3.1.7). To investigate the mechanism of these effects, Ch uptake studies were performed with and without hemicholinium-3 (HC3), a selective inhibitor of high affinity Ch uptake. A two-compartment model accurately fit the observed data and yielded a K(m) for Ch uptake of 5 microM into cholinergic structures and 72 microM into all other cells. Using this model it was estimated that cholinergic neurons account for 60% of observed uptake of Ch at physiologic Ch concentrations, even though they represent fewer than 1% of the total cells in the slice. The model also predicts that an increase in Ch uptake within cholinergic neurons, reported to be associated with depolarization [4,27,32], would significantly inhibit Ch uptake into all other cells, and would account for the observed decrease in PCh synthesis.
利用电刺激的大鼠纹状体灌流切片，研究了脑细胞群体调节胆碱（Ch）流入膜或神经递质生物合成的通量的机制。在1小时的刺激期内，将置于灌流培养基中的[甲基 - 14C]胆碱（[Me - 14C]Ch）放置30分钟，其被整合到组织[14C]磷酸胆碱（PCh）和[14C]磷脂酰胆碱（PtdCh）中。刺激还导致PCh合成受到显著抑制，并且释放到培养基中的[14C]乙酰胆碱（ACh）增加了10倍；但它并未影响组织[14C]ACh水平。这种效应无法通过ATP水平的变化以及胆碱激酶（E.C. 2.7.1.32）或胆碱乙酰转移酶（ChAT）（E.C.2.3.1.7）的动力学特性的变化来解释。为了研究这些效应的机制，在有和没有半胱氨酸 - 3（HC3）（一种高亲和力胆碱摄取的选择性抑制剂）的情况下进行了胆碱摄取研究。一个双室模型准确地拟合了观察到的数据，得出胆碱能结构中胆碱摄取的米氏常数（K(m)）为5微摩尔，所有其他细胞中为72微摩尔。使用该模型估计，即使胆碱能神经元在切片中占总细胞数不到1%，在生理胆碱浓度下，它们在观察到的胆碱摄取中占60%。该模型还预测，据报道与去极化相关的胆碱能神经元内胆碱摄取增加，将显著抑制所有其他细胞对胆碱的摄取，并可解释观察到的PCh合成减少。
