ENDONUCLEOLYTIC DNA FRAGMENTATION IS NOT REQUIRED FOR APOPTOSIS OF CULTURED RAT CEREBELLAR GRANULE NEURONS

Depolarizing concentrations of potassium (K+) promote maturation and s urvival of cerebellar granule neurons in vitro. Withdrawal of potassiu m from differentiated neurons induces morphological and biochemical fe atures of apoptosis, including membrane blebbing, nuclear condensation , activation of caspases, and internucleosomal DNA fragmentation. Sign ificant DNA fragmentation is detectable at 6 h after K+ withdrawal and slowly increases thereafter. Two observations indicate that endonucle olytic DNA degradation is neither required nor sufficient for K+ withd rawal-induced apoptosis in cerebellar granule neurons: (i) neurons are rescued from apoptosis by readdition of K+ up to 8 h after K+ withdra wal, when DNA fragmentation has already occured. (ii) The endonuclease inhibitor, aurintricarboxylic acid, inhibits DNA fragmentation as ass essed by quantitative DNA fluorometry, TUNEL staining, and DNA gel ele ctrophoresis, but not cell death or chromatin condensation induced by K+ withdrawal. (C) 1998 Elsevier Science Ireland Ltd.