Kennedy E D, Challiss R A, Ragan C I, Nahorski S R
Department of Pharmacology and Therapeutics, University of Leicester, U.K.
Biochem J. 1990 May 1;267(3):781-6. doi: 10.1042/bj2670781.
The ability of lithium to interfere with phosphoinositide metabolism in rat cerebral cortex slices has been examined by monitoring the accumulation of CMP-phosphatidate (CMP-PtdOH) and the reduction in Ins(1,4,5)P3 and Ins(1,3,4,5)P4 levels. A small accumulation of [14C]CMP-PtdOH was seen in slices prelabelled with [14C]cytidine and stimulated with carbachol (1 mM) or Li+ (1 mM). However, simultaneous addition of both agents for 30 min produced a 22-fold accumulation, with Li+ producing a half-maximal effect at a concentration of 0.61 +/- 0.19 mM. Kinetic studies revealed that the effects of carbachol and Li+ on CMP-PtdOH accumulation occurred with no initial lag apparent under these conditions and that preincubation with myo-inositol (10 or 30 mM) dramatically attenuated CMP-PtdOH accumulation. myo-Inositol could also attenuate the rate of accumulation of CMP-PtdOH when added 20 min after carbachol and Li+; these effects were not observed when equimolar concentrations of scyllo-inositol were added. Use of specific radioreceptor assays allowed the mass accumulations of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 to be monitored. Following a lag of 5-10 min, Li+ resulted in a marked reduction in the accumulation of both inositol polyphosphates resulting from muscarinic-cholinergic stimulation. Preincubation of cerebral cortex slices with myo- (but not scyllo-) inositol delayed, but did not prevent, the reduction in the accumulation of Ins(1,4,5)P3 or Ins(1,3,4,5)P4. The results suggest that cerebral cortex, at least in vitro, is very sensitive to myo-inositol depletion under conditions of muscarinic receptor stimulation. The relationship of such depletion to the generation of inositol polyphosphate second messengers is discussed.
通过监测CMP - 磷脂酸（CMP - PtdOH）的积累以及肌醇三磷酸（Ins(1,4,5)P3）和肌醇四磷酸（Ins(1,3,4,5)P4）水平的降低，研究了锂干扰大鼠大脑皮层切片中磷酸肌醇代谢的能力。在用[14C]胞苷预标记并经卡巴胆碱（1 mM）或Li +（1 mM）刺激的切片中，观察到[14C]CMP - PtdOH有少量积累。然而，同时加入这两种试剂30分钟会导致积累增加22倍，Li +在浓度为0.61±0.19 mM时产生半数最大效应。动力学研究表明，在这些条件下，卡巴胆碱和Li +对CMP - PtdOH积累的作用没有明显的初始延迟，并且用肌醇（10或30 mM）预孵育可显著减弱CMP - PtdOH的积累。当在卡巴胆碱和Li +加入20分钟后加入肌醇时，也可减弱CMP - PtdOH的积累速率；当加入等摩尔浓度的异肌醇时，未观察到这些效应。使用特异性放射受体测定法可监测Ins(1,4,5)P3和Ins(1,3,4,5)P4的大量积累。在延迟5 - 10分钟后，Li +导致毒蕈碱 - 胆碱能刺激引起的两种肌醇多磷酸积累显著减少。用肌醇（而非异肌醇）预孵育大脑皮层切片可延迟但不能阻止Ins(1,4,5)P3或Ins(1,3,4,5)P4积累减少。结果表明，至少在体外，大脑皮层在毒蕈碱受体刺激条件下对肌醇耗竭非常敏感。讨论了这种耗竭与肌醇多磷酸第二信使生成的关系。
