Contrasting role of Na(+) ions in modulating Cu(+2) or Cd(+2) induced hepatocyte toxicity.
Previously we showed that hepatocyte lysis induced by Cu(+2)/Cd(+2) could be partly attributed to membrane lipid peroxidation induced by Cu(+2) or mitochondrial toxicity induced by Cd(+2) [5]. Changes in Na(+) and Ca(+2) homeostasis induced when Cu(+2) was incubated with hepatocytes markedly differed from that induced by Cd(+2). Na(+) omission from the media or addition of the Na(+)/H(+) exchange inhibitor 5-(N,N-dimethyl)-amiloride markedly increased Cu(+2) cytotoxicity even though Cu(+2) did not increase hepatocyte Na(+) when the media contained Na(+). Intracellular Ca(+2) levels however were markedly increased when the hepatocytes were incubated with Cu(+2) in a Na(+) free media and removing media Ca(+2) with EGTA also prevented Cu(+2) induced hepatocyte cytotoxicity. This suggests that intracellular Ca(+2) accumulation contributes to Cu(+2) induced cytotoxicity and a Na(+)-dependent Ca(+2) transporter is involved in controlling excessive Ca(+2) accumulation caused by Cu(+2). The omission of Cl(-) from the media or addition of glycine, a Cl(-) channel blocker also enhanced Cu induced cytotoxicity. By contrast Cd(+2) induced cytotoxicity was prevented by Na(+) omission from the media or by the addition of 5-(N,N-dimethyl)-amiloride. Furthermore the omission of Cl(-) from the media or addition of glycine also prevented Cd(+2) induced hepatocyte toxicity. A hypotonic media also increased Cd(+2) but not Cu(+2) induced hepatocyte cytotoxicity. This suggests that Cd(+2) but not Cu(+2) cytotoxicity could be partly attributed to disruption of cell volume regulation mechanisms. The increased osmotic load caused by the uncontrolled accumulation of intracellular Na(+) in Cd(+2) treated hepatocytes likely resulted from the activation of Na(+)/H(+) exchanger and the Na(+)/HCO(3)(-) cotransporter by the acidosis and ATP depletion caused by mitochondrial toxicity.
Pourahmad
J
J
Faculty of Pharmacy, University of Toronto, 19 Russell St., Ontario, Toronto, Canada.
O'Brien
P J
PJ
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects*; D002478:Cells, Cultured; D003300:Copper / Q000633:toxicity*; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008954:Models, Biological; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology* / Q000502:physiology*
D002104:Cadmium; C039465:5-dimethylamiloride; D004533:Egtazic Acid; D003300:Copper; D000584:Amiloride; D012964:Sodium; D002118:Calcium