Morimoto T, Popov S, Buckley K M, Poo M M
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Neuron. 1995 Sep;15(3):689-96. doi: 10.1016/0896-6273(95)90156-6.
Following endocytic uptake of acetylcholine (ACh), CHO fibroblasts exhibit Ca(2+)-dependent spontaneous quantal ACh release and depolarization-evoked ACh release, as detected by a whole-cell voltage-clamped myocyte in contact with the fibroblast. CHO fibroblasts transfected with synaptotagmin I, an integral membrane protein of synaptic vesicles, showed a reduced spontaneous quantal ACh release and an enhanced Ca(2+)-evoked ACh release, as compared with control cells. Biochemical and ultrastructural studies of endocytic activity using horseradish peroxidase as a marker further confirmed the inhibitory action of synaptotagmin I on spontaneous vesicular exocytosis and on elevated exocytosis induced by Ca2+. Through inhibition of exocytosis at the resting intracellular concentration of Ca2+ and removal of the inhibition upon depolarization-induced Ca2+ entry, synaptotagmin I could enhance the efficiency of excitation-secretion coupling.
在乙酰胆碱（ACh）通过内吞作用被摄取后，CHO成纤维细胞表现出Ca(2+)依赖性的自发性量子化ACh释放以及去极化诱发的ACh释放，这是通过与成纤维细胞接触的全细胞膜片钳记录的肌细胞检测到的。用突触结合蛋白I（一种突触小泡的整合膜蛋白）转染的CHO成纤维细胞，与对照细胞相比，自发性量子化ACh释放减少，而Ca(2+)诱发的ACh释放增强。使用辣根过氧化物酶作为标记对内吞活性进行的生化和超微结构研究进一步证实了突触结合蛋白I对自发性囊泡胞吐作用以及由Ca2+诱导的增强的胞吐作用的抑制作用。通过在静息细胞内Ca2+浓度下抑制胞吐作用，并在去极化诱导的Ca2+内流时消除这种抑制作用，突触结合蛋白I可以提高兴奋-分泌偶联的效率。
