Accumulation of Ca2+ induced by cytotoxic levels of menadione in the isolated, perfused rat liver.
Previous studies have indicated that the presence of cytotoxic levels of menadione (2-methyl-1,4-naphthoquinone) causes rapid changes in intracellular thiol and Ca2+ homeostasis in isolated rat hepatocytes. The present investigation was undertaken to examine these effects in the intact liver. Rat livers were therefore perfused with Krebs-Henseleit buffer containing 1.3 mM Ca2+ using a single-pass mode, and the perfusate Ca2+ level was monitored with an on-line Ca2+-selective electrode. Infusion of menadione elicited an increased O2 uptake by the liver, followed by a dose-dependent decrease in the perfusate level of Ca2+. Hepatic accumulation of Ca2+ was accompanied by stimulation of cytosolic phosphorylase a activity. Cessation of menadione infusion resulted in gradual recovery of perfusate Ca2+ to base levels. Ca2+ uptake was not accompanied by decreases in reduced pyridine nucleotide or ATP levels in the liver as evidenced by measurements either during maximal Ca2+ uptake or after recovery. However, Ca2+ uptake was correlated with decreased glutathione and increased glutathione disulfide levels in the liver, both of which reversed during recovery from Ca2+ uptake. Moreover, depletion of hepatic glutathione by pretreatment with diethylmaleate resulted in increased Ca2+ uptake during menadione infusion. The amount of protein-bound mixed disulfides showed a particularly striking relationship to Ca2+ uptake, reaching a maximal level during Ca2+ uptake and reversing toward normal value during recovery from Ca2+ accumulation. The present findings suggest that menadione-induced Ca2+ uptake is due to plasma membrane dysfunction as a result of loss of protein thiol groups critical for maintaining the plasma membrane Ca2+ extrusion mechanism. Our model offers a particularly useful opportunity to study mechanisms underlying toxic disturbances in Ca2+ homeostasis in the intact liver, since Ca2+ fluxes can be monitored under conditions in which cellular control mechanisms are not obliterated by excessive toxicity.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D010477:Perfusion; D011506:Proteins / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014812:Vitamin K / Q000633:toxicity*
D004220:Disulfides; D011506:Proteins; D013438:Sulfhydryl Compounds; D014812:Vitamin K; D005978:Glutathione; D002118:Calcium