Mattson M P, Kater S B
Department of Anatomy, Colorado State University, Fort Collins 80523.
J Neurosci. 1987 Dec;7(12):4034-43. doi: 10.1523/JNEUROSCI.07-12-04034.1987.
Neurite outgrowth from isolated, identified molluscan (Helisoma trivolvis) neurons in culture can be suppressed by neurotransmitters and electrical activity, both of which increase intraneuronal Ca2+ levels (Haydon et al., 1984; Cohan et al., 1986, 1987). We explored the possibility of a causal relationship between Ca2+ influx from the cell exterior and neurite outgrowth using a spectrum of pharmacological manipulations known to affect transmembrane Ca2+ flux. Ca2+ ionophore A23187, an agent expected to increase Ca2+ influx, suppressed both elongation and motile growth cone structures (i.e., filopodia and lamellipodia) in a dose-dependent (10(8)-10(6) M) and reversible manner. Furthermore, high concentrations of Ca2+ channel blockers (La3+, Cd2+, Co2+; e.g., 10(-4) M La3+) suppressed both elongation and growth cone movements. These data support previous experiments, which indicated that neurite outgrowth is dependent upon a specific range of intracellular Ca2+ concentrations (Connor, 1986; Cohan et al., 1987). However, tests of the dose-dependency of the effects of Ca2+ channel blockers on outgrowth revealed that specific, low concentrations of Ca2+ channel blockers (e.g., 10(-5) M La3+) caused, simultaneously, a reduction of growth cone filopodia and an acceleration of elongation. Consistent with the results using low levels of Ca2+ channel blockers, reduced extracellular Ca2+-stimulated neurite elongation while suppressing growth cone motility. Finally, neurotransmitter regulation of neurite outgrowth was shown to require influx of extracellular Ca2+; serotonin inhibition of neuron B19 was prevented by La3+ (10(-5) M) or by incubation in a reduced Ca2+ environment. Taken together, these results indicate that there are optimum levels of Ca2+ influx that promote normal neurite elongation and growth cone movements; these 2 components of outgrowth appear to have differential sensitivities to Ca2+.
培养的分离、已鉴定的软体动物（三角帆蚌）神经元的神经突生长可被神经递质和电活动抑制，这两者都会增加神经元内的钙离子水平（海登等人，1984年；科汉等人，1986年、1987年）。我们使用一系列已知会影响跨膜钙离子通量的药理学操作，探讨了细胞外钙离子内流与神经突生长之间因果关系的可能性。钙离子载体A23187是一种预期会增加钙离子内流的试剂，它以剂量依赖性（10⁻⁸ - 10⁻⁶ M）且可逆的方式抑制伸长和动态生长锥结构（即丝状伪足和片状伪足）。此外，高浓度的钙离子通道阻滞剂（镧离子、镉离子、钴离子；例如，10⁻⁴ M镧离子）抑制伸长和生长锥运动。这些数据支持了先前的实验，表明神经突生长取决于细胞内特定范围的钙离子浓度（康纳，1986年；科汉等人，1987年）。然而，对钙离子通道阻滞剂对生长影响的剂量依赖性测试表明，特定的低浓度钙离子通道阻滞剂（例如，10⁻⁵ M镧离子）同时导致生长锥丝状伪足减少和伸长加速。与使用低水平钙离子通道阻滞剂的结果一致，降低细胞外钙离子刺激神经突伸长，同时抑制生长锥运动。最后，神经递质对神经突生长进行调节需要细胞外钙离子内流；10⁻⁵ M镧离子或在低钙离子环境中孵育可阻止血清素对神经元B19的抑制作用。综上所述，这些结果表明存在促进正常神经突伸长和生长锥运动的最佳钙离子内流水平；生长的这两个组成部分对钙离子似乎具有不同的敏感性。
