Effects of temperature on axonal transport and turnover of protein in goldfish optic system
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Tritiated leucine was injected into one eye of goldfish maintained at 20.5 C. After allowing 2 hr for incorporation of the labeled amino acid, one group of fish was transferred to 9 C. The rate of the fast component of protein transport in the optic axons was reduced from about 60 mm/day at 20.5 C to about 20 mm/day at 9 C, giving a Q10 of at least 2.6. The rate of appearance of the initial portion of the slow component remained unchanged, which emphasizes the difference in the mechanisms underlying the two components. At the lower temperature, the fast component showed a sharp early peak not seen at 20.5 C. The turnover of retinal protein showed two phases, a decrease of about 30% over 5-10 days, then an exponential decline with a half-life of about 3 weeks at 20.5 C and a Q10 of 4.5. The locally synthesized proteins in the tectum showed, in addition to the initial synthesis period, an increase in radioactivity between 3 and 10 days after the injection. Eventually the tectal radioactivity declined exponentially with a half-life of about 7 weeks at 20.5 C and a Q10 of 2.2. The total transported radioactivity, on the other hand, showed an over-all decline which was close to linear rather than exponential, with a half-time of about 6 weeks. This lifetime was so much prolonged at the lower temperature that the Q10 could not be determined. From autoradiograms of the tectum it was found that the increase in radioactivity signaling the arrival of the slow component could not be detected in the synaptic endings of the optic fibers where the fast component accumulated. The radioactivity in the endings declined to half in about 90 days at 15 C. © 1972.
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