Grady E F, Gamp P D, Jones E, Baluk P, McDonald D M, Payan D G, Bunnett N W
Department of Surgery, University of California, San Francisco 94143-0660, USA.
Neuroscience. 1996 Dec;75(4):1239-54. doi: 10.1016/0306-4522(96)00357-0.
Neurotransmission depends on the availability of transmitter and on the presence of functional, high-affinity receptors at the plasma membrane that are capable of binding ligand. The pathway, mechanism and function of endocytosis and recycling of the substance P or neurokinin 1 receptor in enteric neurons were studied using fluorescent substance P, receptor antibodies and confocal microscopy. In both the soma and neurites, substance P induced rapid, clathrin-mediated internalization of the neurokinin 1 receptor into early endosomes, which also contained the transferrin receptor. After 4-8 h, there was a return in surface neurokinin 1 receptor immunoreactivity in the soma, which was not prevented by cycloheximide, and was thus independent of new protein synthesis. This return was prevented by acidotropic agents, therefore required endosomal acidification. This suggests that the neurokinin 1 receptor recycles in the soma. In contrast, in neurites, substance P and the neurokinin 1 receptor remained in endosomes and recycling was not detected. Neurons of the myenteric plexus were heavily innervated by substance P-containing nerve fibers, and K(+)-stimulated release of endogenous substance P from cultured neurons induced internalization of the neurokinin 1-receptor. Therefore, endogenous substance P may induce endocytosis of the neurokinin 1 receptor. In the soma, endocytosis and recycling correlated with loss and recovery of functional binding sites for substance P. suggesting that this process contributes to the regulation of peptidergic neurotransmission. Thus, ligand-induced endocytosis of the neurokinin 1 receptor in myenteric neurons is associated with a loss of surface receptors and functional binding sites. Since release of endogenous substance P induces neurokinin 1 receptor internalization, and neurokinin 1 receptor neurons are innervated by substance P-containing fibers, endocytosis of neuropeptide receptors may regulate neurotransmission.
神经传递依赖于神经递质的可用性以及质膜上存在的能够结合配体的功能性高亲和力受体。使用荧光物质P、受体抗体和共聚焦显微镜研究了肠神经元中P物质或神经激肽1受体的内吞作用和再循环的途径、机制及功能。在胞体和神经突中，P物质均诱导神经激肽1受体通过网格蛋白介导快速内化进入早期内体，早期内体中还含有转铁蛋白受体。4 - 8小时后，胞体表面神经激肽1受体免疫反应性恢复，放线菌酮不能阻止这种恢复，因此其独立于新蛋白质合成。这种恢复可被亲酸性药物阻止，因此需要内体酸化。这表明神经激肽1受体在胞体中进行再循环。相反，在神经突中，P物质和神经激肽1受体保留在内体中，未检测到再循环。肌间神经丛的神经元被含P物质的神经纤维大量支配，培养的神经元中K(+)刺激内源性P物质释放可诱导神经激肽1受体内化。因此，内源性P物质可能诱导神经激肽1受体的内吞作用。在胞体中，内吞作用和再循环与P物质功能性结合位点的丧失和恢复相关，提示该过程有助于调节肽能神经传递。因此，肌间神经元中配体诱导的神经激肽1受体内吞作用与表面受体和功能性结合位点的丧失有关。由于内源性P物质的释放诱导神经激肽1受体内化，且神经激肽1受体神经元由含P物质的纤维支配，神经肽受体内吞作用可能调节神经传递。
