Influence of a bearing-wastewater phenolic compound (3,4-dimethylphenol, 3,4-DMP) treatment on Ca2+ homeostasis and its related cytotoxicity in human proximal renal tubular epithelial cells

A lot of phenolic compounds are widespread in industrial effluents and they are considerable environmental pollutants. Being a compound commercially available, the effect of a bearing-wastewater phenolic compound 3,4-dimethylphenol (3,4-DMP) on Ca2+ homeostasis and its related physiology has not been explored in cultured human kidney cell models. The aim of this study was to explore the effect of 3,4-DMP on [Ca2+]i and viability in HK-2 human proximal renal tubular epithelial cells. In terms of Ca2+ signaling, 3,4-DMP (5–100 μM) induced [Ca2+]i rises only in HK-2 cells and Ca2+ removal reduced the signal by 40%. In Ca2+-containing medium, 3,4-DMP-induced Ca2+ entry was inhibited by 20% by a modulator of store-operated Ca2+ channels (2-APB), and by a PKC activator (PMA) and inhibitor (GF109203X). Moreover, 3,4-DMP-induced Mn2+ influx suggesting of Ca2+ entry. In Ca2+-free medium, inhibition of PLC with U73122 abolished 3,4-DMP-induced [Ca2+]i rises. Furthermore, treatment with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin abolished 3,4-DMP-evoked [Ca2+]i rises. Conversely, treatment with 3,4-DMP abolished thapsigargin-evoked [Ca2+]i rises. Regarding to cell viability, 3,4-DMP (60–140 μM) killed cells in a concentration-dependent fashion in HK-2 cells. Chelation of cytosolic Ca2+ with BAPTA-AM partially reversed cytotoxicity of 3,4-DMP. Collectively, our data suggest that in HK-2 cells, 3,4-DMP-induced [Ca2+]i rises by evoking Ca2+ entry via PKC-sensitive store-operated Ca2+ entry and PLC-dependent Ca2+ release from the endoplasmic reticulum. 3,4-DMP also caused cytotoxicity that was linked to preceding [Ca2+]i rises. Our findings provide new insight into the cytotoxic effects of 3,4-DMP and the possible mechanisms underlying these effects.