Mercury-induced Ca 2+ increase and cytotoxicity in renal tubular cells

Abstract

The effect of mercury (Hg 2+), a known nephrotoxicant, on intracellular free Ca 2+ levels ([Ca 2+] i) in Madin Darby canine kidney (MDCK) cells was explored. [Ca 2+] i was measured by using the Ca 2+-sensitive dye fura-2. Hg 2+ increased [Ca 2+] i in a concentration-dependent manner with an EC 50 of 6 μM. The Ca 2+ signal comprised a gradual increase. Removal of extracellular Ca 2+ decreased the Hg 2+-induced [Ca 2+] i increase by 27%, suggesting that the Ca 2+ signal was due to both extracellular Ca 2+ influx and store Ca 2+ release. In Ca 2+-free medium, the Hg 2+-induced [Ca 2+] i increase was nearly abolished by pretreatment with 1 μM thapsigargin (an endoplasmic reticulum Ca 2+ pump inhibitor), and conversely, pretreatment with Hg 2+ abolished thapsigargin-induced Ca 2+ increase. Hg 2+-induced Ca 2+ release was not altered by inhibition of phospholipase C but was potentiated by activation of protein kinase C. Overnight treatment with 1 μM Hg 2+ did not alter cell proliferation rate and mitochondrial activity, but 10 μM Hg 2+ killed all cells. Collectively, this study shows that Hg 2+ induced protein kinase C-regulated [Ca 2+] i increases in renal tubular cells via releasing store Ca 2+ from the endoplasmic reticulum in a manner independent of phospholipase C activity. Hg 2+ also caused cytotoxicity at higher concentrations.