GLIA-TO-AXON COMMUNICATION - ENRICHMENT OF GLIAL PROTEINS TRANSFERREDTO THE SQUID GIANT-AXON

The transfer of newly synthesized proteins from the glial sheath into the axon is a well-documented process for the squid giant axon, In thi s study, me used a novel approach to separate the transferred glial pr oteins (TGPs) from the endogenous axoplasmic proteins of the squid gia nt axon, Axoplasm, containing radiolabelled TGPs, was extruded as a cy linder and immersed in an intracellular buffer, After 1-30 min, the TG Ps were enriched in the intracellular buffer, because they were eluted from the axoplasm into the intracellular buffer much faster than the endogenous axoplasmic proteins. Most of the TGPs enriched in the intra cellular buffer did not pellet when centrifuged at 24,000 g for 20 min and were susceptible to protease digestion without the addition of Tr iton X-100, Additionally, transmission electron microscopic autoradiog raphy of intact axons, containing radiolabelled TGPs, suggested that m ost TGPs were not associated with vesicular organelles within the axon , We conclude that most of the TGPs are not contained within vesicles in the axoplasm of the squid giant axon, as would be expected if the m echanism of glia-to-axon transfer were conventional exocytosisendocyto sis or microphagocytosis. (C) 1995 Wiley-Liss, Inc.