Mercury-induced Ca2+ increase and cytotoxicity in renal tubular cells

摘要

The effect of mercury (Hg2+), a known nephrotoxicant, on intracellular free Ca2+ levels ([Ca2+](i)) in Madin Darby canine kidney (MDCK) cells was explored. [Ca2+](i) was measured by using the Ca2+-sensitive dye fura-2. Hg2+ increased [Ca2+](i) in a concentration-dependent manner with an EC50 of 6 muM. The Ca2+ signal comprised a gradual increase. Removal of extracellular Ca2+ decreased the Hg2+-induced [Ca2+](i) increase by 27%, suggesting that the Ca2+ signal was due to both extracellular Ca2+ influx and store Ca2+ release. In Ca2+-free medium, the Hg2+-induced [Ca2+](i) increase was nearly abolished by pretreatment with 1 muM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), and conversely, pretreatment with Hg2+ abolished thapsigargin-induced Ca2+ increase. Hg2+-induced Ca2+ release was not altered by inhibition of phospholipase C but was potentiated by activation of protein kinase C. Overnight treatment with 1 muM Hg2+ did not alter cell proliferation rate and mitochondrial activity, but 10 muM Hg2+ killed all cells. Collectively, this study shows that Hg2+ induced protein kinase C-regulated [Ca2+](i) increases in renal tubular cells via releasing store Ca2+ from the endoplasmic reticulum in a manner independent of phospholipase C activity. Hg2+ also caused cytotoxicity at higher concentrations. (C) 2004 Elsevier Inc. All rights reserved. [References: 19]