Silver R A, Lamb A G, Bolsover S R
Department of Physiology, University College London, United Kingdom.
J Neurosci. 1989 Nov;9(11):4007-20. doi: 10.1523/JNEUROSCI.09-11-04007.1989.
Schubert (1984) and Kater et al. (1988) have suggested that motility and growth at the neuronal growth cone is activated by an increase of cytosolic free calcium concentration ([Ca2+]i) above the levels found in quiescent growth cones. In order to test this model, we have used a digital imaging fluorescence microscope together with injection of the fluorescent indicator dye Fura-2 to measure [Ca2+]i in growth cones of a mammalian sympathetic neuron, the N1E-115 neuroblastoma cell. The behavior of individual growth cones, together with spontaneously varying levels of [Ca2+]i within the growth cone, were monitored for periods of up to several hours. [Ca2+]i in motile, advancing growth cones was low and equal to [Ca2+]i in quiescent growth cones. Higher values of [Ca2+]i were found in motile growth cones that were not advancing, suggesting that a small elevation of [Ca2+]i inhibits neurite extension. A further rise of [Ca2+]i above the level found in motile, nonadvancing growth cones appeared to inhibit motility and cause retraction of the growth cone back towards the cell body. Spatial gradients of [Ca2+]i within the growth cone were small and, where statistically significant, [Ca2+]i was lower by 5-10 nM in motile regions. Our results are incompatible with the model that a rise of [Ca2+]i is responsible for activating quiescent growth cones; however, our results suggest that in active growth cones [Ca2+]i can regulate morphology and behavior.
舒伯特（1984年）以及卡特等人（1988年）提出，神经元生长锥的运动性和生长是由胞质游离钙浓度（[Ca2+]i）升高至静息生长锥中的水平之上所激活的。为了验证该模型，我们使用了数字成像荧光显微镜，并注射荧光指示剂染料Fura-2来测量哺乳动物交感神经元N1E-115神经母细胞瘤细胞生长锥中的[Ca2+]i。对单个生长锥的行为以及生长锥内[Ca2+]i的自发变化水平进行了长达数小时的监测。运动性的、向前延伸的生长锥中的[Ca2+]i较低，且与静息生长锥中的[Ca2+]i相等。在不向前延伸的运动性生长锥中发现了较高的[Ca2+]i值，这表明[Ca2+]i的小幅升高会抑制神经突的延伸。[Ca2+]i进一步升高至运动性的、不向前延伸的生长锥中的水平之上，似乎会抑制运动性并导致生长锥向细胞体回缩。生长锥内[Ca2+]i的空间梯度较小，且在具有统计学意义的情况下，运动区域中的[Ca2+]i低5-10 nM。我们的结果与[Ca2+]i升高负责激活静息生长锥的模型不一致；然而，我们的结果表明，在活跃的生长锥中，[Ca2+]i可以调节形态和行为。
