Uptake of Protein by the Giant Axon of the Squid

THE uptake of macromolecules by neurones and glia may be relevant to an understanding of the relationships between these cells and to the concept of the glia-neurone unit¹. Protein uptake has been studied biochemically using suspensions of animal cells², but little morphological evidence has been gathered from neuronal systems^3–5. This problem can be investigated conveniently using the giant axon of the squid; biochemical analyses can be carried out on samples of axoplasm after incubation of intact axons with a labelled macromolecule. To do this we have used¹²⁵I-albumin as a model protein because of its commercial availability and the lack of reincorporation of free ¹²⁵I-tyrosine into protein².