Studies on the mechanism of the reversal of rapid organelle transport in myelinated axons of Xenopus laevis

Abstract

Rapid organelle transport was studied by computer- and video-enhanced microscopy in the region of localized lesions in single myelinated axons of Xenopus laevis. Localized lesions were created that were either impermeable to small ions in the bathing medium or were permeable to agents with molecular weights up to 10,000. Providing the axons were bathed in a suitable “internal” medium, organelle transport continued to within a few micrometers of the lesion whether the lesion was permeable or not. Organelles undergoing anterograde and retrograde transport reversed their direction of transport on reaching the lesion. In preparations with lesions that were permeable, nonhydrolyzable analogs of ATP inhibited normally directed and reversed organelle transport. In permeable preparations, vanadate and EDTA inhibited retrograde and reversed retrograde transport at different intra-axonal concentrations; anterograde and reversed anterograde transport were also differentially inhibited. Anterograde and retrograde organelle transport were also shown to be inhibited at different intraaxonal concentrations of vanadate and EDTA. The results provide evidence for the existence of two different axonal transport mechanisms in myelinated axons. The two mechanisms can account for the normally directed and reversed transport of individual organelles.