INITIATION OF FAST AXONAL-TRANSPORT - INVOLVEMENT OF CALCIUM DURING TRANSFER OF PROTEINS FROM GOLGI-APPARATUS TO THE TRANSPORT-SYSTEM

Fast axonal transport of [3H]fucose-labelled glycoproteins was examined in vitro in a preparation of spinal sensory neurons of the bullfrog. Rapidly transported glycoproteins were labelled when dorsal root ganglia were exposed to [3H]fucose, but not when a localized region of spinal nerve trunk was exposed to the labelled sugar; these results are consistent with the general finding that fucosylation occurs predominantly in the Golgi apparatus. Incubation of ganglia and nerve trunks in medium containing 0.18 mM CoCl2 depressed the amount of rapidly transported, [3H]fucose-labelled glycoprotein by approximately 80%. This level of cobalt impairs neither protein synthesis nor incorporation of [3H]fucose into glycoprotein, suggesting that the inhibition of axonal transport by cobalt occurs at a step subsequent to fucosylation. When a 4 mm region of spinal nerve was desheathed, to facilitate access of ions to the axons, cobalt had no effect on fast axonal transport of glycoproteins at the level of the axon: the amount of [3H]fucose-labelled protein was similar in the regions of nerve trunk proximal and distal to the desheathed area. Thus, the cobalt-sensitive step in the transport of glycoproteins is likely to occur in the somata during transfer of the proteins from the Golgi apparatus to the transport system; it is suggested that cobalt antagonizes the action of intracellular calcium ions. An analogy is considered between the processing of fast-transported proteins by neuronal somata and the processing of secretory proteins by pancreatic exocrine cells. © 1979.