Differential transport of protein in axons: comparison between the sciatic nerve and dorsal columns of cats.

Fast axoplasmic transport was studied in dorsal root ganglion cells of the cat. Proteins carried in the fast axoplasmic flow were labeled after an intraganglionic injection of (L)-[4,5-(3)H]leucine. The rate of transport was 380 +/- 26 mm/day in both the central and peripheral branches of the bifurcating axons that arise from cells of the dorsal root ganglion. The amount of radioactivity transported centrally, through the dorsal roots into the spinal cord, was about 50% of that moving peripherally, through the sensory fibers of the sciatic nerve. Labeled material appears to be transported principally in a bound form, as 70-80% of the radioactivity was insoluble in 0.01 M potassium phosphate buffer at pH 7.4. With multiple extractions, a fractionation procedure was developed by which 94-96% of the total transported radioactivity could be solubilized. The proteins carried by fast axoplasmic transport through the dorsal columns and through the sciatic nerve were compared by electrophoresis of extracted fractions on Na dodecyl sulfate-polyacrylamide gels. Different patterns of radioactivity are seen in the electrophoretograms, suggesting that the cells of the dorsal root ganglion may possess the ability to commit different proteins to transport through two branches of a single bifurcating axon.