Ca2+ movement and cytotoxicity induced by the pyrethroid pesticide bifenthrin in human prostate cancer cells

Bifenthrin, a commonly used pyrethroid pesticide, evokes various toxicological effects in different models. However, the effect of bifenthrin on cytosolic-free Ca2+ level ([Ca2+](i)) and cytotoxicity in human prostate cancer cells is unclear. This study examined whether bifenthrin altered Ca2+ homeostasis and cell viability in PC3 human prostate cancer cells. [Ca2+](i) in suspended cells were measured using the fluorescent Ca2+-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 assay. Bifenthrin (100-400 mu M) concentration-dependently induced [Ca2+](i) rises. Ca2+ removal reduced the signal by approximately 30%. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished bifenthrin-evoked [Ca2+](i) rises. Conversely, treatment with bifenthrin abolished BHQ-evoked [Ca2+](i) rises. Inhibition of phospholipase C (PLC) with U73122 significantly inhibited bifenthrin-induced [Ca2+](i) rises. Mn2+ has been shown to enter cells through similar mechanisms as Ca2+ but quenches fura-2 fluorescence at all excitation wavelengths. Bifenthrin (400 mu M)-induced Mn2+ influx implicates that Ca2+ entry occurred. Bifenthrin-induced Ca2+ entry was inhibited by 30% by protein kinase C (PKC) activator (phorbol 12-myristate 13 acetate) and inhibitor (GF109203X) and three inhibitors of store-operated Ca2+ channels: nifedipine, econazole, and SKF96365. Bifenthrin at 175-275 mu M decreased cell viability, which was not reversed by pretreatment with the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N ',N '-tetra acetic acid-acetoxymethyl ester. Together, in PC3 cells, bifenthrin-induced [Ca2+](i) rises by evoking PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-sensitive store-operated Ca2+ entry. Bifenthrin also caused Ca2+-independent cell death.