The mechanism of maitotoxin-induced elevation of the cytosolic free calcium level in rat cerebrocortical synaptosomes.

The present study was conducted to elucidate the mechanism of the maitotoxin (MTX)-induced increase in intrasynaptosomal free calcium level ([Ca2+]i). The MTX (1 ng/ml)-induced increase in [Ca2+]i was partially inhibited by the omission of extracellular Ca2+ (Ca2+e) or the addition of verapamil, but not by adding nifedipine, omega-agatoxin IVA, omega-conotoxin GVIA and omega-conotoxin MVIIC. An increase in [Ca2+]i in the absence of Ca2+e was sensitive to procaine, TMB-8, genistein and verapamil, but not to ryanodine and U-73122. These results may suggest that MTX increases [Ca2+]i by stimulating Ca2+ entry through voltage-independent nonselective cation channels and Ca2+ release from stores through a phospholipase C-gamma1-mediated pathway in rat cerebrocortical synaptosomes.