Cellular mechanisms of plasmalemmal sealing and axonal repair by polyethylene glycol and methylene blue.
Mammalian neurons and all other eukaryotic cells endogenously repair traumatic injury within minutes by a Ca²⁺-induced accumulation of vesicles that interact and fuse with each other and the plasmalemma to seal any openings. We have used uptake or exclusion of extracellular fluorescent dye to measure the ability of rat hippocampal B104 cells or rat sciatic nerves to repair (seal) transected neurites in vitro or transected axons ex vivo. We report that endogenous sealing in both preparations is enhanced by Ca²⁺-containing solutions and is decreased by Ca²⁺-free solutions containing antioxidants such as dithiothreitol (DTT), melatonin (MEL), methylene blue (MB), and various toxins that decrease vesicular interactions. In contrast, the fusogen polyethylene glycol (PEG) at 10-50 mM artificially seals the cut ends of B104 cells and rat sciatic axons within seconds and is not affected by Ca²⁺ or any of the substances that affect endogenous sealing. At higher concentrations, PEG decreases sealing of transected axons and disrupts the plasmalemma of intact cells. These PEG-sealing data are consistent with the hypothesis that lower concentrations of PEG directly seal a damaged plasmalemma. We have considered these and other data to devise a protocol using a well-specified series of solutions that vary in tonicity, Ca²⁺, MB, and PEG content. These protocols rapidly and consistently repair (PEG-fuse) rat sciatic axons in completely cut sciatic nerves in vivo rapidly and dramatically to restore long-lasting morphological continuity, action potential conduction, and behavioral functions.
Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas, USA.
C S
CS
Spaeth
T
T
Robison
J D
JD
Fan
G D
GD
Bittner
D000818:Animals; D000975:Antioxidants / Q000627:therapeutic use; D001369:Axons / Q000187:drug effects*; D019771:Axotomy; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects* / Q000502:physiology; D004195:Disease Models, Animal; D004229:Dithiothreitol / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008550:Melatonin / Q000627:therapeutic use; D008751:Methylene Blue; D009447:Neuroblastoma / Q000473:pathology; D011092:Polyethylene Glycols / Q000494:pharmacology / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020426:Sciatic Neuropathy / Q000188:drug therapy* / Q000473:pathology; D014945:Wound Healing / Q000187:drug effects*
D000975:Antioxidants; D011092:Polyethylene Glycols; D008550:Melatonin; D002118:Calcium; D008751:Methylene Blue; D004229:Dithiothreitol