Maitotoxin, a Ca2+ channel activator candidate.

Effects of maitotoxin, the most potent marine toxin, were studied using a rat pheochromocytoma cell line, PC12h. A low concentration (10(-8) g/ml) of maitotoxin induced a profound increase in CA2+ influx into PC12h cells and the Ca2+-dependent release of [3H]norepinephrine from them. The effects of maitotoxin were not affected by treatment with tetrodotoxin (10(-6) M) and were observed even in the absence of external Na+. Furthermore, these effects were markedly inhibited or abolished by treatment with verapamil (30-300 microM), Mn2+ (5 mM), or tetracaine (1 mM). These results suggest that maitotoxin activates the voltage-dependent calcium channels of PC12h cells.