A COMPARISON OF THE AXONAL TRANSPORT OF TAURINE AND PROTEINS IN THE GOLDFISH VISUAL SYSTEM |
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| Authors: | N A Ingoglia J A Sturman D K Rassin T D Lindquist |
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| Institution: | Departments of Physiology and Neuroscience, New Jersey Medical School, Newark, NJ 07103, U.S.A. and Department of Human Development and Genetics, Institute for Basic Research in Mental Retardation, Staten Island, NY 10314, U.S.A. |
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| Abstract: | Abstract— Radioactive cystathionine, a metabolic precursor of taurine, was injected into the right eye of goldfish. At various times after injection the retina and both optic tecta were extracted with trichloroacetic acid (TCA) and the amount and nature of the radioactivity was determined. Radioactive taurine and inorganic sulfate were present in the TCA-soluble extract of retina and radioactive taurine and a small amount of inorganic sulfate was found in the contralateral optic tectum. That taurine is migrating intraaxonally and is not diffusing in extraaxonal spaces is suggested from experiments in which the migration of taurine was compared with that of 14C]mannitol, used here as a marker of extracellular diffusion. In the time studied (up to 15 h) mannitol did not migrate to the tectum, whereas taurine was detectable in the tectum as early as 8 h after injection. Since intra-axonal diffusion of amino acids and other small molecules in this system has been ruled out, it is likely that taurine is being transported axonally. The axonal transport of taurine was found to be similar to the fast component of protein transport because: (1) their rates of transport are similar, (2) the transport of both is blocked by the protein synthesis inhibitor cycloheximide, (3) vinblastine, which disrupts neurotubules, appears to have similar effects on both protein and taurine transport, and (4) both rapidly transported proteins and taurine remain mostly intra-axonal once they have been transported to the tectum. Taurine and proteins differ in that rapidly transported proteins are primarily paniculate in nature and localized to a large extent in nerve endings, while taurine is primarily in a soluble fraction and is present in nerve endings only in trace amounts. We suggest that taurine may be loosely linked to a newly synthesized protein in the soma and is then transported along with that protein on a similar conveying mechanism in the axoplasm. |
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