Maitotoxin induces calpain but not caspase-3 activation and necrotic cell death in primary septo-hippocampal cultures

Maitotoxin is a potent toxin that activates voltage and receptor-mediated C a2+ channels, resulting in Ca2+ overload and rapid cell death. We report th at maitotoxin-induced cell death is associated with activation of calpain b ut not caspase-3 proteases in septo-hippocampal cell cultures. Calpain and caspase-3 activation were examined by accumulation of protease-specific bre akdown products to a-spectrin. Cell death manifested exclusively necrotic-l ike characteristics including round, shrunken nuclei, even distribution of chromatin, absence of DNA fragmentation and failure of protein synthesis in hibition to reduce cell death. Necrotic cell death was observed in neurons and astroglia. Calpain inhibitor II inhibited calpain-specific processing o f alpha-spectrin and significantly reduced cell death. The pan-caspase inhi bitor, Z-D-DCB, nominally attenuated cell death. Results suggest that: (1) calpain, but not caspase-3, is activated as a result of maitotoxin-induced Ca2+ influx; (2) necrotic cell death caused by maitotoxin exposure is parti ally mediated by calpain activation; (3) maitotoxin is a useful tool to inv estigate pathological mechanisms of necrosis.