Endonucleolytic DNA fragmentation is not required for apoptosis of cultured rat cerebellar granule neurons

Depolarizing concentrations of potassium (K+) promote maturation and survival of cerebellar granule neurons in vitro. Withdrawal of potassium from differentiated neurons induces morphological and biochemical features of apoptosis, including membrane blebbing, nuclear condensation, activation of caspases, and internucleosomal DNA fragmentation. Significant DNA fragmentation is detectable at 6 h after K+ withdrawal and slowly increases thereafter. Two observations indicate that endonucleolytic DNA degradation is neither required nor sufficient for K+ withdrawal-induced apoptosis in cerebellar granule neurons: (i) neurons are rescued from apoptosis by readdition of K+ up to 8 h after K+ withdrawal, when DNA fragmentation has already occurred. (ii) The endonuclease inhibitor, aurintricarboxylic acid, inhibits DNA fragmentation as assessed by quantitative DNA fluorometry, TUNEL staining, and DNA gel electrophoresis, but not cell death or chromatin condensation induced by K+ withdrawal.