Wicher D, Walther C, Wicher C
Sächsische Akademie der Wissenschaften zu Leipzig, Arbeitsgruppe Neurohormonale Wirkungsmechanismen, Erbertstr. 1, 07743, Jena, Germany.
Prog Neurobiol. 2001 Aug;64(5):431-525. doi: 10.1016/s0301-0082(00)00066-6.
Insects are favoured objects for studying information processing in restricted neuronal networks, e.g. motor pattern generation or sensory perception. The analysis of the underlying processes requires knowledge of the electrical properties of the cells involved. These properties are determined by the expression pattern of ionic channels and by the regulation of their function, e.g. by neuromodulators. We here review the presently available knowledge on insect non-synaptic ion channels and ionic currents in neurons and skeletal muscles. The first part of this article covers genetic and structural informations, the localization of channels, their electrophysiological and pharmacological properties, and known effects of second messengers and modulators such as neuropeptides or biogenic amines. In a second part we describe in detail modulation of ionic currents in three particularly well investigated preparations, i.e. Drosophila photoreceptor, cockroach DUM (dorsal unpaired median) neuron and locust jumping muscle. Ion channel structures are almost exclusively known for the fruitfly Drosophila, and most of the information on their function has also been obtained in this animal, mainly based on mutational analysis and investigation of heterologously expressed channels. Now the entire genome of Drosophila has been sequenced, it seems almost completely known which types of channel genes--and how many of them--exist in this animal. There is much knowledge of the various types of channels formed by 6-transmembrane--spanning segments (6TM channels) including those where four 6TM domains are joined within one large protein (e.g. classical Na+ channel). In comparison, two TM channels and 4TM (or tandem) channels so far have hardly been explored. There are, however, various well characterized ionic conductances, e.g. for Ca2+, Cl- or K+, in other insect preparations for which the channels are not yet known. In some of the larger insects, i.e. bee, cockroach, locust and moth, rather detailed information has been established on the role of ionic currents in certain physiological or behavioural contexts. On the whole, however, knowledge of non-synaptic ion channels in such insects is still fragmentary. Modulation of ion currents usually involves activation of more or less elaborate signal transduction cascades. The three detailed examples for modulation presented in the second part indicate, amongst other things, that one type of modulator usually leads to concerted changes of several ion currents and that the effects of different modulators in one type of cell may overlap. Modulators participate in the adaptive changes of the various cells responsible for different physiological or behavioural states. Further study of their effects on the single cell level should help to understand how small sets of cells cooperate in order to produce the appropriate output.
昆虫是研究受限神经元网络中信息处理的理想对象，例如运动模式生成或感官感知。对潜在过程的分析需要了解所涉及细胞的电特性。这些特性由离子通道的表达模式及其功能调节决定，例如通过神经调质进行调节。我们在此综述目前关于昆虫神经元和骨骼肌中非突触离子通道及离子电流的现有知识。本文的第一部分涵盖遗传和结构信息、通道的定位、它们的电生理和药理特性，以及第二信使和调节剂（如神经肽或生物胺）的已知作用。在第二部分中，我们详细描述了在三种研究得特别透彻的标本中离子电流的调节，即果蝇光感受器、蟑螂背中无对神经元和蝗虫跳跃肌肉。离子通道结构几乎仅在果蝇中为人所知，而且关于其功能的大部分信息也是在这种动物中获得的，主要基于突变分析和对异源表达通道的研究。现在果蝇的整个基因组已被测序，似乎几乎完全清楚这种动物中存在哪些类型的通道基因以及它们的数量。对于由六个跨膜片段形成的各种类型的通道（6TM通道），包括那些四个6TM结构域在一个大蛋白质中连接的通道（例如经典的Na +通道），我们有很多了解。相比之下，迄今为止几乎尚未探索双跨膜通道和4TM（或串联）通道。然而，在其他昆虫标本中存在各种特征明确的离子电导，例如对于Ca2 +、Cl-或K +的电导，而其通道尚不清楚。在一些较大的昆虫中，即蜜蜂、蟑螂、蝗虫和蛾类，已经建立了关于离子电流在某些生理或行为背景下作用的相当详细的信息。然而总体而言，此类昆虫中非突触离子通道的知识仍然支离破碎。离子电流的调节通常涉及或多或少复杂的信号转导级联反应的激活。第二部分中给出的三个调节的详细例子表明，除其他外，一种类型的调节剂通常会导致几种离子电流的协同变化，并且不同调节剂在一种类型的细胞中的作用可能会重叠。调节剂参与负责不同生理或行为状态的各种细胞的适应性变化。在单细胞水平上对其作用的进一步研究应有助于理解少量细胞如何协作以产生适当的输出。
