Huang H M, Sun G Y
Biochemistry Department, University of Missouri, Columbia 65203.
J Neurochem. 1988 Feb;50(2):366-74. doi: 10.1111/j.1471-4159.1988.tb02921.x.
Incubation of rat brain synaptosomes prelabeled with [2-3H]inositol resulted in a time-dependent release of labeled inositol 1-phosphate. This process was Ca2+ dependent, and ATP (1 mM) enhanced the inositol 1-phosphate formation three- to fivefold. Using [1-14C]arachidonoyl-phosphatidylinositol which was introduced into saponin-permeabilized synaptosomes, ATP (1 mM) and free Ca2+ (approximately 20 microM) enhanced the phospholipase C hydrolysis of this substrate to form labeled diacylglycerol. When the same permeabilized synaptosomal preparation was incubated with [2-3H]inositol-phosphatidylinositol, ATP not only enhanced the formation of labeled inositol 1-phosphate, but also inhibited the conversion of inositol 1-phosphate to inositol. Furthermore, ATP appeared to reduce the Ca2+ requirement of the phosphatidylinositol-phospholipase C. Inhibition of the conversion of inositol 1-phosphate to inositol could not be overcome by increasing the Mg2+ concentration in the incubation medium. Although the ATP effect is not viewed as a receptor-mediated event, it is possible that such an event may occur in synaptosomes under conditions in which intrasynaptic Ca2+ concentration becomes elevated.
用[2-³H]肌醇预先标记的大鼠脑突触体进行温育，导致标记的肌醇1-磷酸呈时间依赖性释放。这个过程依赖于Ca²⁺，并且ATP（1 mM）可使肌醇1-磷酸的形成增加三到五倍。使用引入皂素通透化突触体中的[1-¹⁴C]花生四烯酰磷脂酰肌醇，ATP（1 mM）和游离Ca²⁺（约20 μM）可增强该底物的磷脂酶C水解，形成标记的二酰基甘油。当相同的通透化突触体制剂与[2-³H]肌醇磷脂酰肌醇一起温育时，ATP不仅增强了标记的肌醇1-磷酸的形成，还抑制了肌醇1-磷酸向肌醇的转化。此外，ATP似乎降低了磷脂酰肌醇-磷脂酶C对Ca²⁺的需求。通过增加孵育培养基中的Mg²⁺浓度并不能克服肌醇1-磷酸向肌醇转化的抑制作用。尽管ATP的作用不被视为受体介导的事件，但在突触内Ca²⁺浓度升高的条件下，这种事件可能在突触体中发生。
