Axonal L-type Ca2+ channels and anoxic injury in rat CNS white matter.
We studied the magnitude and route(s) of Ca2+ flux from extra- to intracellular compartments during anoxia in adult rat optic nerve (RON), a central white matter tract, using Ca2+ sensitive microelectrodes to monitor extracellular [Ca2+] ([Ca2+]o). One hour of anoxia caused a rapid loss of the stimulus-evoked compound action potential (CAP), which partially recovered following re-oxygenation, indicating that irreversible injury had occurred. After an initial increase caused by extracellular space shrinkage, anoxia produced a sustained decrease of 0.42 mM (29%) in [Ca2+]o. We quantified the [Ca2+]o decrease as the area below baseline [Ca2+]o during anoxia and used this as a qualitative index of suspected Ca2+ influx. The degree of RON injury was predicted by the amount of Ca2+ leaving the extracellular space. Bepridil, 0 Na+ artificial cerebrospinal fluid or tetrodotoxin reduced suspected Ca2+ influx during anoxia implicating reversal of the Na+/Ca2+ exchanger as a route of Ca2+ influx. Diltiazem reduced suspected Ca2+ influx during anoxia, suggesting that Ca2+ influx via L-type Ca2+ channels is a route of toxic Ca2+ influx into axons during anoxia. Immunocytochemical staining was used to demonstrate and localize high-threshold Ca2+ channels. Only alpha1(C) and alpha1(D) subunits were detected, indicating that only L-type Ca2+ channels were present. Double labeling with anti-neurofilament antibodies or anti-glial fibrillary acidic protein antibodies localized L-type Ca2+ channels to axons and astrocytes.
Brown
A M
AM
Department of Neurology, University of Washington School of Medicine, Seattle, Washington 98195, USA. ambrown@u.washington.edu
Westenbroek
R E
RE
Catterall
W A
WA
Ransom
B R
BR
D000818:Animals; D001369:Axons / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology*; D007150:Immunohistochemistry; D009900:Optic Nerve / Q000378:metabolism* / Q000473:pathology*; D009994:Osmolar Concentration; D051381:Rats; D020318:Rats, Long-Evans; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D014018:Tissue Distribution
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D019831:Sodium-Calcium Exchanger