Differential effects of cobalt on the initiation of fast axonal transport

Effects of Co²⁺ on the fast axonal transport of individual proteins were examined in vitro in bullfrog spinal/sciatic nerves.³⁵S-methionine-labeled proteins, fast-transported in control and Co²⁺-treated preparations were separated via two-dimensional gel electrophoresis. While the overall amount of protein transported was reduced, no qualitative differences could be seen when gel fluorographic patterns were compared. Quantitative analyses of the 48 most abundantly transported species revealed two significantly different populations (p < 0.01) differentially sensitive to Co²⁺ and distinguishable to a large extent by molecular weight. Those proteins less sensitive to Co²⁺ ranged from ~20,000 to 35,000 daltons while those more sensitive to Co²⁺ were >~35,000 daltons. The finding that all proteins are affected by Co²⁺ supports the proposal that fast-transported proteins are subject to a common Co²⁺-sensitive, Ca²⁺-requiring step. The observed differential effects are consistent with more than one Ca²⁺-dependent step occurring during the initiation phase of fast transport.This research was supported by a Muscular Dystrophy Association postdoctoral fellowship to G.C.S., and by research grants from NSF (BNS 79-24125) and the National Multiple Sclerosis Society (RG 1296-A-1) to R.H.