title: Evidence for a direct role of intracellular calcium in paracetamol toxicity.
abstract: There is considerable evidence that an increase in cytosolic Ca2+ is involved in the cytotoxicity of a variety of agents. However, the direct demonstration of such involvement has proved difficult. In the present study, loading of freshly isolated hamster hepatocytes with the Ca2+ specific chelator Quin 2 (2-[(2-bis[carboxymethyl]amino-5-methyl-phenoxy)methyl]-6-methoxy-8- bis-[carboxymethyl]amino-quinoline) provided significant protection against the loss of viability caused by paracetamol. This was evident both when the cells were co-incubated with Quin 2-AM and paracetamol, and when the cells were incubated with Quin 2-AM after prior exposure to paracetamol and its complete removal from the hepatocytes. These observations provide direct evidence that an increase in intracellular Ca2+ is the cause of cell death in hepatocytes exposed to paracetamol. Further, the fact that Quin 2 is protective even after some time suggests that, for alterations of cytosolic Ca2+ to be detrimental, they must be sustained. The effects of Quin 2 on plasma membrane blebbing of paracetamol-exposed hepatocytes were less pronounced than on cell viability. This is in contrast to the effects of the direct-acting thiol-reducing reducing agent, dithiothreitol, which was equally effective in preventing blebbing and loss of viability. It is concluded that alterations of cytosolic Ca2+ are less directly linked to plasma membrane blebbing than to loss of cell viability.
authors.affiliation: Department of Clinical Pharmacology, Royal Postgraduate Medical School, London, U.K.
authors.forename: A R
authors.initials: AR
authors.lastname: Boobis
authors.forename: C E
authors.initials: CE
authors.lastname: Seddon
authors.forename: P
authors.initials: P
authors.lastname: Nasseri-Sina
authors.forename: D S
authors.initials: DS
authors.lastname: Davies
mesh_terms: D000082:Acetaminophen / Q000037:antagonists & inhibitors / Q000633:toxicity*; D000634:Aminoquinolines / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D002614:Chelating Agents / Q000494:pharmacology*; D006224:Cricetinae; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008647:Mesocricetus
chemical_list: D000634:Aminoquinolines; D002614:Chelating Agents; D000082:Acetaminophen; C035738:Quin2-acetoxymethyl ester; D002118:Calcium; D004229:Dithiothreitol