MAITOTOXIN INDUCES CALPAIN ACTIVATION IN SH-SY5Y NEUROBLASTOMA-CELLS AND CEREBROCORTICAL CULTURES

Maitotoxin (MTX) is a highly potent marine toxin that activates both v oltage-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 activa tion in both SH-SY5Y neuroblastoma cells and fetal rat cerebrocortical cultures. MTX-induced calpain activation was confirmed by the presenc e of autolytic fragmentation of both subunits of calpain. Secondly, th e formation of calpain-produced cu-spectrin breakdown products (150 an d 145 kDa) was observed. We were also able to detect intracellular hyd rolysis of a peptide substrate succinyl-Leu-Leu-Val-Tyr-7-amido-4-meth ylcoumarin) by activated calpain in MTX-treated cells. Calpain inhibit ors (calpain inhibitor I, MDL28170 and PD150606) inhibited spectrin br eakdown and SLLVY-AMC hydrolysis in MTX-treated SY5Y cells, Our result s suggest that (i) calpain is activated as a result of the maitotoxin- induced calcium influx; and (ii) coupling with the in situ calpain ass ays, maitotoxin would be a useful tool in investigating the physiologi c and pathophysiologic roles of calpain in neuronal cells. (C) 1996 Ac ademic Press, Inc.