Fisher S K, Agranoff B W
J Neurochem. 1981 Oct;37(4):968-77.
Addition of either acetylcholine (ACh) or the ionophore A23187 to synaptopsomes resulted in a selective stimulation of 32Pi incorporation into phosphatidate (PhA) and phosphatidylinositol (PhI), while the labeling of phosphatidylinositol phosphate (PhIP) and phosphatidylinositol diphosphate (PHIP2) was reduced. The inclusion of both ACh and A23187 resulted in a synergistic increase in PhA and PhI labeling, and a synergistic decrease in the labeling of the polyphosphoinositides. Added calcium was not required, although inclusion of EGTA prevented the alterations in lipid labeling. The enhanced labeling of PhA and PhI by ACh or A23187 was not the result of either an increase in the radioactivity of the precursor [32P]ATP pool, or increased de novo synthesis of these lipids as judged from the incorporation of [3H]glycerol, [3H]glucose or [3H]myo-inositol. The synergistic alterations in PhA, PhI, and polyphosphoinositide labeling were observed with ionophore only in the presence of selected muscarinic agonists, and with the inclusion of atropine or scopolamine the labeling reverted to a value which approximated that seen with the ionophore alone. Synergistic effects on phospholipid labeling with muscarinic agonists were also obtained with the calcium ionophore, ionomycin, but not with X537A, monensin, or valinomycin. Neither the apparent number of muscarinic receptors present, nor their affinity for the ligand were altered by the presence of A23187. In prelabeling experiments, A23187 accelerated the loss of [32P]label from PhIP and PhIP2, and the rate of loss was further augmented by the addition of ACh. Neither agent produced comparable effects on the breakdown of prelabeled PhA or PhI. It is suggested that phosphodiesteratic cleavage of the polyphosphoinositides might account for both the decrease in labeled PhIP and PhIP2 and increased labeling of PhA and PhI via the availability of resultant diglyceride. In any event, the results demonstrate that the turnover of polyphosphoinositides, in addition to that of PhA and PhI, is linked to the activation of muscarinic receptors.
向突触体中添加乙酰胆碱（ACh）或离子载体A23187会选择性地刺激32Pi掺入磷脂酸（PhA）和磷脂酰肌醇（PhI），而磷脂酰肌醇磷酸（PhIP）和磷脂酰肌醇二磷酸（PHIP2）的标记则减少。同时加入ACh和A23187会导致PhA和PhI标记协同增加，而多磷酸肌醇的标记协同减少。虽然加入EGTA可防止脂质标记的改变，但添加钙并非必需。ACh或A23187增强PhA和PhI的标记并非前体[32P]ATP池放射性增加的结果，也不是根据[3H]甘油、[3H]葡萄糖或[3H]肌醇的掺入判断的这些脂质从头合成增加的结果。仅在存在特定毒蕈碱激动剂的情况下，离子载体才会观察到PhA、PhI和多磷酸肌醇标记中的协同变化，加入阿托品或东莨菪碱后，标记恢复到接近单独使用离子载体时的值。钙离子载体离子霉素也能与毒蕈碱激动剂对磷脂标记产生协同作用，但X537A、莫能菌素或缬氨霉素则不能。A23187的存在既不改变毒蕈碱受体的表观数量，也不改变其对配体的亲和力。在预标记实验中，A23187加速了PhIP和PhIP2中[32P]标记的丢失，加入ACh后丢失速率进一步加快。两种试剂对预标记的PhA或PhI的分解均未产生类似影响。有人认为，多磷酸肌醇的磷酸二酯酶裂解可能是标记的PhIP和PhIP2减少以及通过生成甘油二酯导致PhA和PhI标记增加的原因。无论如何，结果表明，除了PhA和PhI的周转外，多磷酸肌醇的周转与毒蕈碱受体的激活有关。
