Depolarization maintains neurites and priming of PC12 cells after nerve growth factor withdrawal.
In contrast to its actions on certain neural populations, membrane depolarization by elevated K+ promotes neither the survival nor the differentiation of PC12 cells. We therefore employed this model system to examine directly the actions of elevated K+ on neurites. Here we report that elevated K+ prevents the degeneration of neurites that occurs when NGF is withdrawn from PC12 cell cultures. This effect is inhibited by the L-type Ca2+ channel blockers verapamil and nitrendipine. Although depolarization preserves preexisting neurites, unlike NGF, it does not promote neurite elongation. In addition to neurite stabilization, elevated K+ also maintains NGF-deprived cells in a "primed" state in which they can rapidly regenerate neurites when re-treated with NGF. Elevated K+ alone has no priming effect, nor is it neuritogenic on either naive or NGF-pretreated cells. To probe the molecular basis for these actions of depolarization, we examined several cytoskeletal proteins whose phosphorylations (beta-tubulin, MAP 1.2/1B, and 64, 72 and 80 kDa chartins) or levels (MAP 1.2/1B and peripherin) are regulated by NGF in parallel with neurite outgrowth. Elevated K+ alone does not mimic these effects of NGF. In all cases, NGF withdrawal leads to the return of these proteins to levels characteristic of naive cells; in contrast, with the exception of the 80 kDa chartins, depolarization of NGF-deprived cultures maintained these proteins at or near their NGF-stimulated states. Similar observations were obtained with the NILE/L1 glycoprotein. These findings suggest that elevated K+ preserves priming and preexisting neurites by maintaining NGF-induced changes in cell composition. Our experiments invoke the possibility that elevation of intraneuronal Ca2+ may lead to selective stabilization of preexisting axons or dendrites in the intact nervous system, especially under circumstances in which the supply of neurotrophic factors is absent or limiting.
Teng
K K
KK
Department of Pathology, Columbia University, College of Physicians and Surgeons, New York, New York 10032.
Greene
L A
LA
D000818:Animals; D003598:Cytoskeletal Proteins / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008854:Microscopy, Electron; D009414:Nerve Growth Factors / Q000494:pharmacology*; D016501:Neurites / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009568:Nitrendipine / Q000494:pharmacology; D016716:PC12 Cells; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology*; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology
D003598:Cytoskeletal Proteins; D009414:Nerve Growth Factors; D010750:Phosphoproteins; D009568:Nitrendipine; D014700:Verapamil; D011188:Potassium