Effect of methoxychlor on Ca²⁺ homeostasis and apoptosis in HA59T human hepatoma cells

Methoxychlor, an organochlorine pesticide, is thought to be an endocrine disrupter that affects Ca²⁺ homeostasis and cell viability in different cell models. This study explored the action of methoxychlor on cytosolic free Ca²⁺ concentrations ([Ca²⁺]i) and apoptosis in HA59T human hepatoma cells. Fura-2, a Ca²⁺-sensitive fluorescent dye, was applied to measure [Ca²⁺]i. Methoxychlor at concentrations of 0.1-1 μM caused a [Ca²⁺]i rise in a concentration-dependent manner. Removal of external Ca²⁺ abolished methoxychlor's effect. Methoxychlor-induced Ca²⁺ influx was confirmed by Mn²⁺-induced quench of fura-2 fluorescence. Methoxychlor-induced Ca²⁺ entry was inhibited by nifedipine, econazole, SK&F96365, and protein kinase C modulators. Methoxychlor killed cells at concentrations of 10-130 μM in a concentration-dependent fashion. Chelation of cytosolic Ca²⁺ with 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid/AM (BAPTA/AM) did not prevent methoxychlor's cytotoxicity. Methoxychlor (10 and 50 μM) induced apoptosis concentration-dependently as determined by using Annexin V/propidium iodide staining. Together, in HA59T cells, methoxychlor induced a [Ca²⁺]i rise by inducing Ca²⁺ entry via protein kinase C-sensitive Ca²⁺-permeable channels, without causing Ca²⁺ release from stores. Methoxychlor also induced apoptosis that was independent of [Ca²⁺]i rises.