Axoplasmic transport of free amino acids

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1. (1) Following the injection of l-[14C]proline into one eye in carp, the label appeared in the contralateral optic nerve via axoplasmic flow. As reported previously, protein-bound activity showed faster and slower axoplasmic transport. Labeled free proline appeared in nerve before labeled protein and thus did not originate from labeled protein. 2. (2) When [14C]α-aminoisobutyric acid, l-proline, or d-glutamic acid was injected into the eye, the label in the nerve decreased in a distal direction. The radioactivity gave two peaks of maximal activity with time in the whole nerve and in nerve sections, indicating a faster and a slower component of the axoplasmic transport of amino acids. There were no peaks of activity in the nerve on the control side. Estimated transport rates for the fast components were 90-110 mm/day; values for the slow component varied between 5 and 20 mm/day. The acid-soluble activity did not reach the end of the optic tact or the optic lobe in significant quantities. 3. (3) The injected tracer amino acid levels rapidly declined in the eye; the rate of exit was different for the various compounds. The amino acid content in the eye or in the circulation did not seem to influence the measured flow significantly. The amino acids were not restricted to the external portion of the nerve but along with their axonal flow left the nerve via exchange or exit. 4. (4) Axonal transport in the goldfish optic system occured at rates similar to those in carp. In goldfish a sharp temperature gradient of axonal transport could be measured with a maximum at 20 °C. Axonal amino acid transport in chick and rabbit nerve was about 3 times as fast as in fish, possibly because of higher body temperature. 5. (5)_The composition of the free amino acid pool is characteristic for the various peripheral nerves and is different from that in brain. Some of its components have a proximo-distal concentration gradient. Axonal transport of amino acids may play a part in maintaining such gradient or in regulating amino acid metabolism in nerve.

Original languageEnglish
Pages (from-to)271-284
Number of pages14
JournalBrain research
Issue numberC
Publication statusPublished - Jun 29 1973

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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