Maitotoxin Induces Calpain Activation in SH-SY5Y Neuroblastoma Cells and Cerebrocortical Cultures

Maitotoxin (MTX) is a highly potent marine toxin that activates both voltage-sensitive and receptor-operated calcium channels in the plasma membrane. This results in calcium overload that rapidly leads to cell death. We now report that maitotoxin (0.1–1 nM) induces calpain activation in both SH-SY5Y neuroblastoma cells and fetal rat cerebrocortical cultures. MTX-induced calpain activation was confirmed by the presence of autolytic fragmentation of both subunits of calpain. Secondly, the formation of calpain-produced α-spectrin breakdown products (150 and 145 kDa) was observed. We were also able to detect intracellular hydrolysis of a peptide substrate (succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin) by activated calpain in MTX-treated cells. Calpain inhibitors (calpain inhibitor I, MDL28170 and PD150606) inhibited spectrin breakdown and SLLVY-AMC hydrolysis in MTX-treated SY5Y cells. Our results suggest that (i) calpain is activated as a result of the maitotoxin-induced calcium influx; and (ii) coupling with thein situcalpain assays, maitotoxin would be a useful tool in investigating the physiologic and pathophysiologic roles of calpain in neuronal cells.