Ionic Requirements for Rapid Axonal Transportin vitroin Frog Sciatic Nerves

Abstract

The effects of K+, Na+, hypo- and hypertonicity on the synthesis and fast axonal transport of 3H-leucine-labelled protein were studied in vitro in the frog sciatic system. The methodology used made it possible to discriminate between effects on synthesis and transport of protein. The preparation which consisted of the dorsal ganglia, the sciatic nerve and the gastrocnemius muscle was placed in an incubation chamber. The ganglia were incubated in standard Ringer containing 3H-leucine and the nerve was prefused with modified Ringer. Perfusion of the nerve for 17 h with K+-free Ringer of Na+-free Ringer did not affect the rapid axonal transport of 3H-leucine-labelled material from the ganglia along the nerve towards a ligature in front of which it accumulated. Not was the transport influenced by concentrations of K+ up to 68.8 mM. In contrast concentrations exceeding 100 mM K+ partially inhibited the transport. Inhibition by ouabain (0.1 mM) was not prevented by elevating K+ to 30 mM, Deviation from isotonicity, towards a hypo- or a hypertonic medium, partially inhibited axonal transport. The transport inhibitory effects showed reversibility. Expermintal conditions, which arrested the transport, were tested in spearate experiments for effects on uptake of 3H-leucine into TCA-soluble and insoluble ganglionic components. K+ substituted for Na+, ouabain (0.1 mM) and hypotonic Ringer partially inhibited the amino acid uptake but also subsequent steps in the incorporation process, whereas only the latter was inhibited by hypertonic Ringer. The results are discussed in relation to possible changes in energy metabolism.