Mechano-electric transduction and dynamics of cytoskeletons in mechanoreceptor cells

众所周知，昆虫中存在三种类型的机械感受器，它们在结构和形态上彼此不同。本研究用快速冷冻电镜技术研究了三种昆虫机械感受器的机械-电转换的形态学基础。1）研究了蟑螂触角、果蝇和蝗虫股骨的弦音器结构。它们的感觉纤毛与运动纤毛相似，细长，轴丝上有染色质臂。机械刺激前后纤毛的形态学比较表明，感觉纤毛的主动摆动或被动摆动可能参与了机械-电转换。2）观察了蟑螂触角和果蝇笼头钟状感器的结构。它们的感觉纤毛的特点是在远端的管状体，这被称为一束微管。对快速冷冻标本的观察表明，肌动蛋白丝出现在管状体的微管之间。这两种丝状体的规则排列可能是钟状感受器力电转换的形态学基础。这种细胞骨架的解聚导致受体敏感性的降低。3）在蝗虫翅膀中检测了拉伸受体的结构。拉伸受体的细胞体很大（高达50 μ m），并延伸出许多树突，这些树突必须是受体位点。4）本研究的结果表明，昆虫的三种机械感受器都具有其特有的机械-电转换初级过程，这与感受器区细胞骨架的特殊结构密切相关。

It is widely known that there are three types of mechanoreceptors in insects, which structurally and morphologically differ from each other. In the present study morphological basis of mechano-electric transduction has been examined in the three types of insect mechanoreceptors by means of rapid freezing techniques for electron microscopy.1) The structure of the chordotonal organ was examined in cockroach antennae, Drosophila halteres, and locust femurs. Their sensory cilia show some similarity to motile cilia, being thin and long and possessing axoneme with dyenin arms. Morphological comparison between mechanically stimulated cilia and un-stimulated ones suggests that active stroke or passive waving of the sensory cilia may be involved in the mechano-electric transduction.2) The structure of the campaniform sensillum was examined in cockroach antennae and Drosophila halteres. Their sensory cilia are characterized by the tubular body in the distal tip, which is known as a bundle of microtubules. The observation of rapid frozen specimens revealed that actin filaments occur among microtubules in the tubular body. Regular arrangement of the two types of filaments may comprise morphological basis of mechano-electric transduction in the campaniform sensilla. Depolymerization of such cytoskeleton resulted in reduction of receptor sensitivity.3) The structure of the stretch receptor was examined in locust wings. The cell body of the stretch receptors is large (up to 50 mum) and extends many dendrites, which must be receptor sites. Actin filaments were densely localized in the dendritic regions.4) The data obtained in the present study suggest that three types of the insect mechanoreceptors possess their specific primary processes of the mechano-electric transduction, which is closely related to specific organization of cytoskeleton in the receptor region.