guanosine-5--o-(2-thiodiphosphate) and Carcinoma--Hepatocellular

Mercury is a non-essential heavy metal affecting intracellular Ca2+ dynamics. We studied the effects of Hg2+ on [Ca2+]i in trout hepatoma cells (RTH-149). Confocal imaging of fluo-3-loaded cells showed that Hg2+ induced dose-dependent, sustained [Ca2+]i transient, triggered intracellular Ca2+ waves, stimulated Ca2+-ATPase activity, and promoted InsP3 production. The effect of Hg2+ was reduced by the Ca2+ channel blocker verapamil and totally abolished by extracellular GSH, but was almost unaffected by cell loading with the heavy metal chelator TPEN or esterified GSH. In a Ca2+-free medium, Hg2+ induced a smaller [Ca2+]i transient, that was unaffected by TPEN, but was abolished by U73122, a PLC inhibitor, and by cell loading with GDP-betaS, a G protein inhibitor, or heparin, a blocker of intracellular Ca2+ release. Data indicate that Hg2+ induces Ca2+ entry through verapamil-sensitive channels, and intracellular Ca2+ release via a G protein-PLC-InsP3 mechanism. However, in cells loaded with heparin and exposed to Hg2+ in the presence of external Ca2+, the [Ca2+]i rise was maximally reduced, indicating that the global effect of Hg2+ is not a mere sum of Ca2+ entry plus Ca2+ release, but involves an amplification of Ca2+ release operated by Ca2+ entry through a CICR mechanism.

Topics: Aniline Compounds; Animals; Ca(2+) Mg(2+)-ATPase; Calcium; Calcium Signaling; Carcinoma, Hepatocellular; Cell Line, Tumor; Cytosol; Estrenes; Ethylenediamines; Glutathione; GTP-Binding Proteins; Guanosine Diphosphate; Heparin; Histocytochemistry; Inositol 1,4,5-Trisphosphate; Kinetics; Mercury; Microscopy, Confocal; Microscopy, Fluorescence; Phospholipases; Pyrrolidinones; Thionucleotides; Trout; Verapamil; Xanthenes