Inhibition and stimulation of rapid axonal transport in vitro by sulfhydryl blockers

The effects of sulfhydryl blocking agents have been studied on the rapid axonal transport in vitro of [3H]leucine-labelled proteins in the frog sciatic nerve. The transport was inhibited in the presence of low concentrations of N-ethylmaleimide (NEM) (greater than or equal to 10(-5) M), p-chloromercuribenzene sulfonic acid (PCMBS) (greater than 10(-5) M) or ions of heavy metals, Cd2+ (greater than or equal to 5 X 10(-5) M), Hg2+ (greater than or equal to 5 X 10(-6) M) and Cu2+(greater than or equal to 10(-4) M). Both the amount and the rate of transported radioactivity were reduced. Transport inhibiting concentrations of these agents also inhibited the binding of colchicine in rat brain or frog nerve supernatants. The amount of transported proteins was increased at an unchanged transport rate by a very low concentration of NEM (10(-6) M), PCMBS (10(-6) M) and Cd2+ (10(-6)M), which did not affect the binding of colchicine. The present results suggest that stimulation of axonal transport can be achieved through an interaction with sulfhydryl groups.