Sensitivity of an insect mechanoreceptor after destruction of dendritic microtubules by means of vinblastine.

Microtubules (Mt) are present in the modified cilium of epithelial mechanoreceptors of insects in three different arrangements: (1) 9 doublet Mt in the proximal region of the outer segment, (2) densely packed, interconnected Mt of the tubular body in the dendritic tip receiving the adequate stimuli, and (3) Mt between ciliary neck and tubular body, which are not fixed in a special configuration and therefore called free Mt. The free Mt are considered by some authors to be elements of intracellular signal transmission. This hypothesis was examined by electrophysiological and morphological studies on a tibial hair-mechanoreceptor of a cricket (Acheta domesticus). Exposure of the receptor from the apical side to vinblastine disassembled the free Mt within 2 to 4 h, while Mt of the tubular body were only little affected during this time interval. In this state of Mt disassembly (up to 7 h of application) mechanosensitivity of the receptor is only slightly reduced or not at all. The pacemaker property of the dendrite for nerve impulse is also preserved. It is concluded that the free Mt are not elements of intracellular signal transmission and are not directly involved in mechanotransduction.