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

Abstract

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.