Retrograde transport and steady-state distribution of 125I-nerve growth factor in rat sympathetic neurons in compartmented cultures.
We have used compartmented cultures of rat sympathetic neurons to quantitatively examine the retrograde transport of 125I-nerve growth factor (NGF) supplied to distal axons and to characterize the cellular events that maintain steady-state levels of NGF in cell bodies. In cultures allowed to reach steady-state 125I-NGF transport, cell bodies contained only 5-30% of the total neuron-associated 125I-NGF, whereas 70-95% remained associated with the distal axons. This was true over an 8 pM to 1.5 nM 125I-NGF concentration range, indicating that saturation of high affinity receptors could not account for the large fraction of 125I-NGF remaining in axons. Dissociation assays indicated that 85% of 125I-NGF associated with distal axons was surface-bound. At steady-state, only 2-25% of the distal axon-associated 125I-NGF was retrogradely transported each hour, with higher transport rates associated with younger cultures and lower 125I-NGF concentrations. The velocity of 125I-NGF retrograde transport was estimated at 10-20 mm/hr. However, as in a previous report, almost no 125I-NGF transport was observed during the first hour after 125I-NGF administration, indicating a significant lag between receptor binding and loading onto the retrograde transport system. During 125I-NGF transport through axons spanning an intermediate compartment in five-compartment cultures, little or no 125I-NGF was degraded or released from the axons. After transport, 125I-NGF was degraded with a half-life of 3 hr. In summary, although some cellular events promoted NGF accumulation in cell bodies, distal axons represented by far the principal site of NGF-receptor interaction at steady-state as a result of a low retrograde transport rate.
Ure
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DR
Department of Cell Biology and Anatomy, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Campenot
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RB
D000818:Animals; D001369:Axons / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D006706:Homeostasis; D007457:Iodine Radioisotopes; D009414:Nerve Growth Factors / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D014018:Tissue Distribution
D007457:Iodine Radioisotopes; D009414:Nerve Growth Factors