Uncovering malathion (an organophosphate insecticide)action on Ca²⁺ signal transduction and investigating the effects of BAPTA-AM (a cell-permeant Ca²⁺ chelator)on protective responses in glial cells

Malathion, one of commonly used organophosphate insecticides, has a wide range of toxic actions in different models. However, the effect of this compound on Ca²⁺ homeostasis and its related cytotoxicity in glial cells is elusive. This study examined whether malathion evoked intracellular Ca²⁺ concentration ([Ca²⁺]_i)rises and established the relationship between Ca²⁺ signaling and cytotoxicity in normal human astrocytes, rat astrocytes and human glioblastoma cells. The data show that malathion induced concentration-dependent [Ca²⁺]_i rises in Gibco^® Human Astrocytes (GHA cells), but not in DI TNC1 normal rat astrocytes and DBTRG-05MG human glioblastoma cells. In GHA cells, this Ca²⁺ signal response was reduced by removing extracellular Ca²⁺. In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin abolished malathion-induced [Ca²⁺]_i rises. Conversely, incubation with malathion abolished thapsigargin-induced [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC)with U73122 also blocked malathion-induced [Ca²⁺]_i rises. In Ca²⁺-containing medium, malathion-induced [Ca²⁺]_i rises was inhibited by store-operated Ca²⁺ channel blockers (2-APB, econazole or SKF96365)and the protein kinase C (PKC)inhibitor GF109203X. Malathion (5–25 μM)concentration-dependently caused cytotoxicity in GHA, DI TNC1 and DBTRG-05MG cells. This cytotoxic effect was partially prevented by prechelating cytosolic Ca²⁺ with BAPTA-AM (a selective Ca²⁺ chelator)only in GHA cells. Together, in GHA but not in DI TNC1 and DBTRG-05MG cells, malathion induced [Ca²⁺]_i rises by inducing PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ channels. Furthermore, malathion induced Ca²⁺-associated cytotoxicity, suggesting that Ca²⁺ chelating may have a protective effect on malathion-induced cytotoxicity in normal human astrocytes.