Luther P W, Yip R K, Bloch R J, Ambesi A, Lindenmayer G E, Blaustein M P
Department of Physiology, University of Maryland, School of Medicine, Baltimore 21201.
J Neurosci. 1992 Dec;12(12):4898-904. doi: 10.1523/JNEUROSCI.12-12-04898.1992.
Calcium ions play a critical role in neurotransmitter release. The cytosolic Ca2+ concentration ([Ca2+]cyt) at nerve terminals must therefore be carefully controlled. Several different mechanisms, including a plasmalemmal Na/Ca exchanger, are involved in regulating [Ca2+]cyt. We employed immunofluorescence microscopy with polyclonal antiserum raised against dog cardiac sarcolemmal Na/Ca exchanger to determine the distribution of the exchanger in vertebrate neuromuscular preparations. Our data indicate that the Na/Ca exchanger is concentrated at the neuromuscular junctions of the rat diaphragm. The exchanger is also present in the nonjunctional sarcolemma, but at a much lower concentration than in the junctional regions. Denervation markedly lowers the concentration of the exchanger in the junctional regions; this implies that the Na/Ca exchanger is concentrated in the presynaptic nerve terminals. In Xenopus laevis nerve and muscle cell cocultures, high concentrations of the exchanger are observed along the neurites as well as at the nerve terminals. The high concentrations of Na/Ca exchanger at presynaptic nerve terminals in vertebrate neuromuscular preparations suggest that the exchanger may participate in the Ca-dependent regulation of neurotransmitter release. The Na/Ca exchanger is also abundant in developing neurites and growth cones, where it may also be important for Ca2+ homeostasis.
钙离子在神经递质释放过程中发挥着关键作用。因此，必须严格控制神经末梢处的胞质钙离子浓度（[Ca2+]cyt）。包括质膜钠钙交换体在内的几种不同机制参与了对[Ca2+]cyt的调节。我们使用针对犬心肌肌膜钠钙交换体产生的多克隆抗血清进行免疫荧光显微镜检查，以确定该交换体在脊椎动物神经肌肉制剂中的分布。我们的数据表明，钠钙交换体集中在大鼠膈肌的神经肌肉接头处。该交换体也存在于非接头肌膜中，但其浓度远低于接头区域。去神经支配显著降低了接头区域交换体的浓度；这意味着钠钙交换体集中在突触前神经末梢。在非洲爪蟾神经和肌肉细胞共培养物中，沿着神经突以及神经末梢观察到高浓度的交换体。脊椎动物神经肌肉制剂中突触前神经末梢处高浓度的钠钙交换体表明，该交换体可能参与神经递质释放的钙依赖性调节。钠钙交换体在发育中的神经突和生长锥中也很丰富，在那里它对钙离子稳态可能也很重要。
