TY - JOUR
T1 - Mechanisms of injury-induced calcium entry into peripheral nerve myelinated axons
T2 - Role of reverse sodium-calcium exchange
AU - Lehning, Ellen J.
AU - Doshi, Renu
AU - Isaksson, Norman
AU - Stys, Peter K.
AU - LoPachin, Richard M.
PY - 1996/2
Y1 - 1996/2
N2 - To investigate the route of axonal Ca2+ entry during anoxia, electron probe x-ray microanalysis was used to measure elemental composition of anoxic tibial nerve myelinated axons after in vitro experimental procedures that modify transaxolemmal Na+ and Ca2+ movements. Perfusion of nerve segments with zero-Na+/Li+-substituted medium and Na+ channel blockade by tetrodotoxin (1 μM) prevented anoxia-induced increases in Na and Ca concentrations of axoplasm and mitochondria. Incubation with a zero- Ca2+/EGTA perfusate impeded axonal and mitochondrial Ca accumulation during anoxia but did not affect characteristic Na and K responses. Inhibition of Na+-Ca2+ exchange with bepridil (50 μM) reduced significantly the Ca content of anoxio axons although mitochondrial Ca remained at anoxic levels. Nifedipine (10 μM), an L-type Ca2+ channel blocker, did not alter anoxia- induced changes in axonal Na, Ca, and K. Exposure of normoxic control nerves to tetrodotoxin, bepridil, or nifedipine did not affect axonal elemental composition, whereas both zero-Ca2+ and zero-Na+ solutions altered normal elemental content characteristically and significantly. The findings of this study suggest that during anoxia, Na+ enters axons via voltage-gated Na+ channels and that subsequent increases in axoplasmic Na+ are coupled functionally to extraaxonal Ca2+ import. Intracellular Na+-dependent, extraaxonal Ca2+ entry is consistent with reverse operation of the axolemmal Na+-Ca2+ exchanger, and we suggest that this mode of Ca2+ influx plays a general role in peripheral nerve axon injury.
AB - To investigate the route of axonal Ca2+ entry during anoxia, electron probe x-ray microanalysis was used to measure elemental composition of anoxic tibial nerve myelinated axons after in vitro experimental procedures that modify transaxolemmal Na+ and Ca2+ movements. Perfusion of nerve segments with zero-Na+/Li+-substituted medium and Na+ channel blockade by tetrodotoxin (1 μM) prevented anoxia-induced increases in Na and Ca concentrations of axoplasm and mitochondria. Incubation with a zero- Ca2+/EGTA perfusate impeded axonal and mitochondrial Ca accumulation during anoxia but did not affect characteristic Na and K responses. Inhibition of Na+-Ca2+ exchange with bepridil (50 μM) reduced significantly the Ca content of anoxio axons although mitochondrial Ca remained at anoxic levels. Nifedipine (10 μM), an L-type Ca2+ channel blocker, did not alter anoxia- induced changes in axonal Na, Ca, and K. Exposure of normoxic control nerves to tetrodotoxin, bepridil, or nifedipine did not affect axonal elemental composition, whereas both zero-Ca2+ and zero-Na+ solutions altered normal elemental content characteristically and significantly. The findings of this study suggest that during anoxia, Na+ enters axons via voltage-gated Na+ channels and that subsequent increases in axoplasmic Na+ are coupled functionally to extraaxonal Ca2+ import. Intracellular Na+-dependent, extraaxonal Ca2+ entry is consistent with reverse operation of the axolemmal Na+-Ca2+ exchanger, and we suggest that this mode of Ca2+ influx plays a general role in peripheral nerve axon injury.
KW - Acrylamide
KW - Anoxia
KW - Electron probe x-ray microanalysis
KW - Myelinated axons
KW - Na-Ca exchanger
KW - Peripheral nerve
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U2 - 10.1046/j.1471-4159.1996.66020493.x
DO - 10.1046/j.1471-4159.1996.66020493.x
M3 - Article
C2 - 8592118
AN - SCOPUS:0030047415
SN - 0022-3042
VL - 66
SP - 493
EP - 500
JO - Journal of Neurochemistry
JF - Journal of Neurochemistry
IS - 2
ER -