McFarlane M B, Gilly W F
Department of Molecular & Cellular Physiology, Hopkins Marine Station of Stanford University, Pacific Grove, CA 93950, USA.
Proc Natl Acad Sci U S A. 1996 May 14;93(10):5067-71. doi: 10.1073/pnas.93.10.5067.
Whole-cell voltage clamp was used to investigate the properties and spatial distribution of fast-deactivating (FD) Ca channels in squid giant fiber lobe (GFL) neurons. Squid FD Ca channels are reversibly blocked by the spider toxin omega-Agatoxin IVA with an IC50 of 240-420 nM with no effect on the kinetics of Ca channel gating. Channels with very similar properties are expressed in both somatic and axonal domains of cultured GFL neurons, but FD Ca channel conductance density is higher in axonal bulbs than in cell bodies at all times in culture. Channels presumably synthesized during culture are preferentially expressed in the growing bulbs, but bulbar Ca conductance density remains constant while Na conductance density increases, suggesting that processes determining the densities of Ca and Na channels in this extrasomatic domain are largely independent. These observations suggest that growing axonal bulbs in cultured GFL neurons are not composed entirely of "axonal" membranes because FD Ca channels are absent from the giant axon in situ but, rather, suggest a potential role for FD Ca channels in mediating neurotransmitter release at the motor terminals of the giant axon.
采用全细胞电压钳技术研究鱿鱼巨大纤维叶（GFL）神经元中快速失活（FD）钙通道的特性和空间分布。鱿鱼FD钙通道可被蜘蛛毒素ω-芋螺毒素IVA可逆性阻断，IC50为240 - 420 nM，对钙通道门控动力学无影响。在培养的GFL神经元的胞体和轴突区域均表达具有非常相似特性的通道，但在培养过程中的所有时间，轴突球部的FD钙通道电导密度均高于细胞体。推测在培养过程中合成的通道优先在生长中的球部表达，但球部钙电导密度保持恒定，而钠电导密度增加，这表明在这个胞外区域决定钙通道和钠通道密度的过程在很大程度上是独立的。这些观察结果表明，培养的GFL神经元中生长的轴突球部并非完全由“轴突”膜组成，因为在原位的巨大轴突中不存在FD钙通道，相反，提示FD钙通道在介导巨大轴突运动终末神经递质释放中可能发挥作用。
