Influence of Temperature on the Velocity and on the Isotope Profile of Slowly Transported Labeled Proteins

Abstract

Abstract— Slow intra‐axonal flow of [3H]leucine labeled proteins has been studied in the garfish olfactory nerve. Because of the homogeneity of the nerve a very well defined peak of slowly transported radioactivity is observed. The velocity of slow flow increases linearly with temperature. Between 14 and 28°C, the rate of the peak apex increases from 0.26 to 1.57 mm/day and the rate of the leading edge of the wavefront from 0.54 to 2.75 mm/day. Extrapolation of the rate‐temperature function indicates that slow flow should stop at 11°C. However, a velocity of 0.1 mm/day was determined for experiments conducted at 10°C. Between 15 and 25°C a Q10 of 3.7 was determined for the peak apex and of 3.3 for the leading edge of the wavefront. The Q10's are significantly larger than the value of 2.2 found for fast transport (Gross & Beidler, 1975) and support the possibility of at least partial differences between the mechanisms of fast and slow transport. A very small peak was found to migrate in front of the main peak. The positioning of this peak seems to be similar to one found by Lasek & Hoffman (1976) in rat ventral motor neurons. A temperature dependent exponential decrease of the slow moving peak height was measured and it can be estimated that only 1% of the slowly transported radioactivity reaches the synapses. Most of the slow radioactivity appears to remain in the axon behind the peak. The plateau height was also found to decrease exponentially with time. The rate of disappearance greatly affects the profile determined by the slowly transported labeled proteins along the nerve.

Slow axoplasmic transport under scrutiny

“…In efferent axons of the chick less than 15 mm long, over 90% of the radioactivity leaving cell bodies does not reach the terminals (Droz et al, 1973), i.e., proteins disappear in transit. The radioactivity of waves decreases consistently with time as they progress along the axon (Williard et al, 1974;Hoffman and Lasek, 1975;Cancalon, 1979;Mori et al, 1979), a fact clearly illustrated by our case study (Fig. 1, A).…”

Maintenance and degradation of proteins in intact and severed axons: implications for the mechanisms of long-term survival of anucleate crayfish axons

“…In MGAs and other axons (Grafstein and Forman, 1980) the bulk of labeled transported protein is conveyed in the slow component, a large proportion of which is deposited in proximal axonal segments as the slow wave moves down the fibers (Schonbach et al, 1973;Cancalon, 1979Cancalon, , 1982. It is not known whether these transported proteins turn over at rates similar to other cellular proteins or whether they are in some way modified and protected from degradation.…”

Patterns of slow transport in sensory nerves

“…A more irregular pattern of outflow was seen. Our results, the waves of Lasek and Hoffman (1976), and the more regular slow waves seen in the garfish olfactory nerve fibers by Cancalon (1979) were accounted for by a process of local dropoff and turnover related to the transport filament mechanism, the "unitary hypothesis" of axoplasmic transport, as will be discussed. A preliminary account of this study has been given in abstract form (Stromska and Ochs, 1977).…”

“…We may account for the wavelike appearance seen in some of our nerves, by Lasek and Hoffman (19751, and the much more regular waves reported by Cancalon (1979) by the "unitary hypothesis," namely, the dropoff, exchange, and redistribution of labeled materials carried down by fast transport mechanism (Ochs, 1975a, 197513). The components contributed to slow transport are those which drop off the transport mechanism sooner than those which remain to be carried down to the nerve terminals.…”