Cohan C S, Connor J A, Kater S B
Department of Biology, University of Iowa, Iowa City 52242.
J Neurosci. 1987 Nov;7(11):3588-99. doi: 10.1523/JNEUROSCI.07-11-03588.1987.
In the present report we used the calcium indicator fura-2 to compare intracellular levels of free calcium in growth cones of isolated Helisoma neurons under a variety of experimental conditions. We tested whether 2 different signals that inhibit growth cone motility--action potentials and serotonin--changed calcium levels in growth cones. Electrical stimulation of the cell body caused a rise in calcium levels at the growth cone. After brief stimulation, calcium levels quickly recovered to normal values, whereas longer stimulation periods required longer recovery times. The application of serotonin to growth cones caused an increase in calcium levels that was selective for growth cones of neurons whose outgrowth was inhibited by serotonin, but not for neurons whose outgrowth was not affected. We also found that motile growth cones had higher free calcium levels than growth cones that had spontaneously stopped growing. Furthermore, the distribution of calcium in neurons that contained motile growth cones was heterogeneous; calcium levels were always higher in the growth cone than in the neurite or soma. These data indicate that calcium levels in growth cones vary in different states of outgrowth and that calcium levels can be modulated by both electrical and chemical signals.
在本报告中，我们使用钙指示剂fura - 2，在多种实验条件下比较分离的椎实螺神经元生长锥内的游离钙水平。我们测试了两种抑制生长锥运动的不同信号——动作电位和血清素——是否会改变生长锥中的钙水平。对细胞体进行电刺激会导致生长锥处的钙水平升高。短暂刺激后，钙水平迅速恢复到正常值，而较长的刺激时间则需要更长的恢复时间。将血清素应用于生长锥会导致钙水平升高，这种升高对其生长受血清素抑制的神经元的生长锥具有选择性，而对其生长不受影响的神经元则没有。我们还发现，可运动的生长锥比自发停止生长的生长锥具有更高的游离钙水平。此外，含有可运动生长锥的神经元中钙的分布是不均匀的；生长锥中的钙水平总是高于神经突或细胞体中的钙水平。这些数据表明，生长锥中的钙水平在不同的生长状态下会有所不同，并且钙水平可以被电信号和化学信号调节。
