Evaluation of the calcium mobilizing action of acetaminophen and bromobenzene in rat hepatocyte cultures.
Acetaminophen (APAP) and bromobenzene (BrB) are reported to selectively inhibit plasma membrane (PM) but not endoplasmic reticulum (ER) Ca2+ transport in rat liver (1). The ability of these hepatotoxicants to increase cytoplasmic Ca2+ levels as a result of disrupted Ca2+ pumping was determined in cultured rat hepatocytes by monitoring the activity of glycogen phosphorylase alpha, a Ca2+ -sensitive (via phosphorylase kinase) enzyme. Following exposure to 2.5 to 10 mM APAP for five minutes, dose-dependent increases in phosphorylase alpha activity were observed (58 to 190 U/g protein). Endoplasmic reticulum Ca2+ pump activity was not inhibited after any dose of APAP (56 nmol Ca2+ per milligram protein per 30 minutes). Phosphorylase alpha activity remained elevated for 60 minutes after exposure to APAP (124 microliters/g protein). Following exposure to 0.5 to 2 mM BrB for five minutes, phosphorylase alpha activity also increased (58 to 229 U/g protein) in a dose-related manner. Endoplasmic reticulum Ca2+ pump activity was inhibited after BrB exposure (from 58 to 16 nmol Ca2+ per milligram protein per 30 minutes). Phosphorylase alpha activity remained elevated for 60 minutes after exposure to BrB (147 U/g protein). Evidence of elevated cytoplasmic Ca2+ is consistent with the inhibition of Ca2+ -extruding/sequestering mechanisms at hepatocyte PM and/or ER. Prolonged elevation of cytosolic Ca2+ levels could overstimulate Ca2+ -sensitive processes within liver cells and thus initiate or contribute to hepatotoxic injury.
Long
R M
RM
Department of Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
Moore
L
L
D000082:Acetaminophen / Q000494:pharmacology*; D000818:Animals; D001969:Bromobenzenes / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000032:analysis; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010762:Phosphorylase a / Q000378:metabolism; D051381:Rats
D001969:Bromobenzenes; D000082:Acetaminophen; D000242:Cyclic AMP; D010762:Phosphorylase a; D002118:Calcium