Birman S, Israël M, Lesbats B, Morel N
J Neurochem. 1986 Aug;47(2):433-44. doi: 10.1111/j.1471-4159.1986.tb04520.x.
In previous work, it was shown that cytoplasmic acetylcholine decreased on stimulation of Torpedo electric organ or synaptosomes in a strictly calcium-dependent manner. This led to the hypothesis that the presynaptic membrane contained an element translocating acetylcholine when activated by calcium. To test this hypothesis, the presynaptic membrane constituents were incorporated into the membranes of liposomes filled with acetylcholine. The proteoliposomes thus obtained released the transmitter in response to a calcium influx. The kinetics and calcium dependency of acetylcholine release were comparable for proteoliposomes and synaptosomes. The presynaptic membrane element ensuring calcium-dependent acetylcholine release is most probably a protein, since it was susceptible to Pronase, but only when the protease had access to the intracellular face of the presynaptic membrane. Postsynaptic membrane fractions contained very low amounts of this protein. It was extracted from the presynaptic membrane under alkaline conditions in the form of a protein-lipid complex of large size and low density which was partially purified. The specificity of the calcium-dependent release for acetylcholine was tested with proteoliposomes filled with equal amounts of acetylcholine and choline or acetylcholine and ATP. In both cases, acetylcholine was released preferentially. After cholate solubilization and gel filtration, the protein ensuring the calcium-dependent acetylcholine release was recovered at a high apparent molecular weight (between 600,000 and 200,000 daltons), its apparent sedimentation coefficient being 17S after cholate elimination. This protein is probably an essential coin of the transmitter release mechanism. We propose to name it mediatophore.
在先前的研究中发现，电刺激电鳐电器官或突触体时，细胞质中的乙酰胆碱会以严格的钙依赖方式减少。这引发了一个假说，即突触前膜含有一种在被钙激活时能转运乙酰胆碱的成分。为了验证这一假说，将突触前膜成分整合到充满乙酰胆碱的脂质体膜中。由此得到的蛋白脂质体在钙内流时会释放递质。蛋白脂质体和突触体释放乙酰胆碱的动力学及钙依赖性具有可比性。确保钙依赖性乙酰胆碱释放的突触前膜成分很可能是一种蛋白质，因为它对链霉蛋白酶敏感，但只有当蛋白酶能够接触到突触前膜的细胞内表面时才会如此。突触后膜部分所含的这种蛋白质极少。它是在碱性条件下从突触前膜中以一种大尺寸、低密度的蛋白质 - 脂质复合物形式提取出来的，并经过了部分纯化。用充满等量乙酰胆碱和胆碱或乙酰胆碱和ATP的蛋白脂质体测试了钙依赖性释放对乙酰胆碱的特异性。在这两种情况下，乙酰胆碱都是优先释放。经胆酸盐溶解和凝胶过滤后，确保钙依赖性乙酰胆碱释放的蛋白质在高表观分子量（600,000至200,000道尔顿之间）处被回收，去除胆酸盐后其表观沉降系数为17S。这种蛋白质可能是递质释放机制的一个关键要素。我们提议将其命名为介质载体。
