Calpain Inhibitors Confer Biochemical, but Not Electrophysiological, Protection Against Anoxia in Rat Optic Nerves

• Published in: Journal of neurochemistry 2000-05, Vol.74 (5), p.2101-2107
• Main Authors: Jiang, Qiubo, Stys, Peter K.
• Format: Article
• Language: English
• Subjects: Animals; Anoxia; Axon; Calcium; Calcium - pharmacology; Calpain - antagonists & inhibitors; Cysteine Proteinase Inhibitors - pharmacology; Dipeptides - pharmacology; Electrophysiology; Glycoproteins - pharmacology; Hypoxia - metabolism; Hypoxia - physiopathology; Ion Channel Gating; Male; Optic Nerve - metabolism; Optic Nerve - physiopathology; Oxygen - pharmacology; Rats; Rats, Long-Evans; Sodium channel; Sodium Channel Blockers; Sodium Channels - physiology; Spectrin; Spectrin - metabolism; Tetrodotoxin - pharmacology; Time Factors; White matter
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2000.0742101.x

: Calpains are ubiquitous Ca2+‐activated neutral proteases that have been implicated in ischemic and traumatic CNS injury. Ischemia and trauma of central white matter are dependent on Ca2+ accumulation, and calpain overactivation likely plays a significant role in the pathogenesis. Adult rat optic nerves, representative central white matter tracts, were studied in an in vitro anoxic model. Functional recovery following 60 min of anoxia and reoxygenation was measured electrophysiologically. Calpain activation was assessed using western blots with antibodies against calpain‐cleaved spectrin breakdown products. Sixty minutes of in vitro anoxia increased the amount of spectrin breakdown ≈20‐fold over control, with a further increase after reoxygenation to >70 times control, almost as much as 2 h of continuous anoxia. Blocking voltage‐gated Na+ channels with tetrodotoxin or removing bath Ca2+ was highly neuroprotective electrophysiologically and resulted in a marked reduction of spectrin degradation. The membrane‐permeable calpain inhibitors MDL 28,170 and calpain inhibitor‐l (10‐100 μM) were effective at reducing spectrin breakdown in anoxic and reoxygenated optic nerves, but no electrophysiological improvement was observed. We conclude that calpain activation is an important step in anoxic white matter injury, but inhibition of this Ca2+‐dependent process in isolation does not improve functional outcome, probably because other deleterious Ca2+‐activated pathways proceed unchecked.