title: Mechanism of chemical-induced toxicity. II. Role of extracellular calcium.
abstract: Previous studies disagree as to if chemical-induced cell death is caused by the influx and accumulation of extracellular Ca2+. To determine the role of extracellular Ca2+ in toxic cell death, the viability (leakage of intracellular K+ and lactate dehydrogenase) and total Ca2+ content of isolated hepatocytes incubated in the presence or absence of extracellular Ca2+ were determined during a toxic insult with bromobenzene, ethyl methanesulfonate (EMS), Ca2+ ionophore A23187, and adriamycin (ADR) in combination with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). The present study utilized the dibutyl phthalate separation technique which enabled the analysis of only viable hepatocytes for changes in intracellular Ca2+ and K+ content during toxic cell injury. The three chemical treatments, bromobenzene, EMS, and ADR-BCNU, each caused an accelerated loss of viability in hepatocytes incubated without extracellular Ca2+ as compared to cells incubated with Ca2+. Furthermore, the total Ca2+ content of viable hepatocytes incubated in the presence of extracellular Ca2+ did not increase during chemically induced cell injury as compared to control cells. In fact, a significant decline in total cellular Ca2+ was observed in viable hepatocytes incubated in Ca2+-free medium during toxic cell injury. Treatment with Ca2+ ionophore A23187 was also toxic to hepatocytes incubated in the presence or absence of extracellular Ca2+. At high concentrations of ionophore (20 microM or 4 micrograms/10(6) cells), cell death was accelerated in hepatocytes incubated with Ca2+ as compared to cells incubated in Ca2+-free medium. In contrast, after treatment with lower concentrations of ionophore (10 microM or 2 micrograms/10(6) cells), the rate of cell death was reversed with hepatocytes incubated without extracellular Ca2+ dying first. Thus, depending on the concentration of A23187 and the time of exposure, the presence of extracellular Ca2+ can be shown either to accelerate or protect against cell death. Surprisingly, reversible and irreversible cell injury were not observed in hepatocytes incubated with extracellular Ca2+ and 2 microM A23187 though this treatment resulted in an 800% increase in total intracellular Ca2+ content. We conclude that chemical-induced hepatic cell death is not caused by an increase in total cellular Ca2+ resulting from the influx of extracellular Ca2+.
authors.forename: M W
authors.initials: MW
authors.lastname: Fariss
authors.forename: D J
authors.initials: DJ
authors.lastname: Reed
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000633:toxicity*; D002118:Calcium / Q000032:analysis / Q000502:physiology*; D002251:Carbon Tetrachloride / Q000633:toxicity*; D002330:Carmustine / Q000633:toxicity*; D002469:Cell Separation; D002470:Cell Survival / Q000187:drug effects; D056486:Chemical and Drug Induced Liver Injury; D004338:Drug Combinations; D004347:Drug Interactions; D005020:Ethyl Methanesulfonate / Q000633:toxicity*; D005110:Extracellular Space / Q000032:analysis; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000032:analysis; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008099:Liver / Q000187:drug effects*; D010472:Perchlorates / Q000633:toxicity*; D051381:Rats
chemical_list: D004338:Drug Combinations; D010472:Perchlorates; D000001:Calcimycin; D005020:Ethyl Methanesulfonate; D002251:Carbon Tetrachloride; D007770:L-Lactate Dehydrogenase; D002118:Calcium; D002330:Carmustine