Rapid transport of phosphatidylcholine occurring simultaneously with protein transport in the frog sciatic nerve

Abstract

1. Either l-[4,5-3H]leucine or [Me-3H]choline, or both l-[U-14C]leucine and [Me-3H]-choline, were injected into the ninth dorsal root ganglion of the frog, and peripheral transport of labelled proteins and/or phospholipids, mostly phosphatidylcholine, was studied by analysis of consecutive segments of the sciatic nerve. 2. At 25°C, approx. 5% of the3H-labelled protein was transported at the rate of 152mm/day. The rate was temperature-dependent with the Q10 value of 2.6. The flow was completely blocked by the local application of colchicine, but was unaffected by cytochalasin D. 3. [Me-3H]-Choline was incorporated into phosphatidylcholine at a comparatively slow rate, but was transported in the nerve at a rate equivalent to that for3H-labelled proteins. 4. The simultaneous transport of phosphatidylcholine and the protein was further supported in the double-labelling experiments by an identical transport rate of3H-labelled phosphatidylcholine and14C-labelled proteins, by their identical temperature dependence, by simultaneous blockade with colchicine, and also by the parallel distribution of the two labels in subcellular fractions. Specific radioactivities on a protein basis of both3H and14C labels were highest in microsomal subfractions enriched with Na+-plus-K+-stimulated adenosine triphosphatase and acetylcholinesterase. It is suggested that3H-labelled phosphatidylcholine and14C-labelled proteins transported in the nerve reside in the same structural entity, most probably a membrane component.