Abstract

Rabbit sciatic nerves were incubated in vitro with local cooling of their proximal or distal regions to produce local accumulations and depletions of acetylcholinesterase (AChE) undergoing rapid axonal transport. Some nerves were also exposed to echothiophate, an anticholinesterase that is partially selective for external or extracellular enzyme. Samples from various regions of the treated nerves were analyzed by differential ultracentrifugation. Particulate AChE activity was found to be transported at a higher average velocity than soluble activity. Somewhat surprisingly, the latter fraction was more sensitive to echothiophate than was the former. On sucrose density gradients, three forms of AChE were resolved, with sedimentation coefficients of 4S, 10S, and 16S. All three forms were subject both to orthograde and to retrograde axonal transport. The 10S form, which predominated in control samples, was also responsible for most of the accumulation of AChE activity at the borders of cooled regions, but the percentage changes were much larger for the 16S form. Although the results indicated large differences among the average transport velocities of the molecular forms of AChE, these differences are probably explained by differences in the proportion of moving enzyme rather than in the true velocity. The echothiophate-sensitivity of the forms of AChE followed the order, 4S > 10S > 16S, but the differences among forms were not statistically significant, suggesting a similar distribution of these forms between internal and external compartments.