Maitotoxin-Induced Phosphoinositide Hydrolysis Is Dependent on Extracellular but Not Intracellular Ca2+ in Human Astrocytoma Cells.

Since maitotoxin, a potent marine toxin, is known to cause not only Ca2+ influx but also phosphoinositide hydrolysis, we investigated the Ca2+ dependency of maitotoxin-induced phosphoinositide hydrolysis in 1321N1 human astrocytoma cells. Maitotoxin elicited inositol 1,4,5-trisphosphate accumulation in a time-dependent manner. In [3H]inositol-labeled cells, maitotoxin stimulated phosphoinositide hydrolysis in an extracellular Ca2+-dependent manner. Maitotoxin also caused an intracellular Ca2+ elevation, which was abolished by an intracellular Ca2+ chelater BAPTA-AM. Interestingly, maitotoxin still caused phosphoinositide hydrolysis in the BAPTA-AM-treated cells. These results indicate that maitotoxin-induced phosphoinositide hydrolysis is dependent on extracellular but not intracellular Ca2+ in 1321N1 human astrocytoma cells.