title: Increase vs. decrease of calcium uptake by isolated heart cells induced by H2O2 vs. HOCl.
abstract: Adult rat heart myocytes were labeled rapidly with exogenous [45Ca2+]. Addition of 2.5 mM H2O2 to the heart cell suspension raised the content of rapidly exchangeable intracellular Ca2+ twofold, whereas addition of 1-30 mM HOCl decreased the Ca2+ content. The H2O2-induced increase in Ca2+ content was dependent on the medium Na+, pH, and temperature but was not significantly affected by addition of verapamil, diltiazem, amiloride, or 3-aminobenzamide. The [3H]ouabain binding to myocytes was suppressed by H2O2, whereas the Ca2+ efflux from myocytes was not influenced. An uncoupler, carbonyl cyanide m-chlorophenylhydrazone, reduced Ca2+ content, implying that the H2O2-induced change in Ca2+ content was not directly related to ATP depletion. On the other hand, the H2O2-induced Ca2+ accumulation in myocytes was prevented by deferoxamine or o-phenanthroline. These results suggest that H2O2 inhibited Na+-K+-ATPase, resulting in an increase in intracellular Na+ concentration and stimulation of sarcolemmal Na+-Ca2+ exchange activity, which caused a transient net Ca2+ influx into myocytes. By contrast, HOCl decreased the Ca2+ content of the rapidly exchangeable pool below control levels and this action of HOCl was antagonized by 1,4-dithiothreitol. HOCl accelerated Ca2+ efflux from myocytes. Ca2+ uptake and Ca2+-ATPase of the isolated sarcoplasmic reticular (SR) fraction were highly sensitive to the action of HOCl. Ca2+ uptake by intracellular sites, studied with myocytes permeabilized with digitonin, was inhibited by both H2O2 and HOCl. Thus these results suggest that HOCl inhibits the SR Ca2+ pump, resulting in the observed acceleration of Ca2+ efflux from and decline in Ca2+ content of myocytes.
authors.affiliation: Department of Physiology, University of Ottawa, School of Medicine, Ontario, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Kaminishi
authors.forename: T
authors.initials: T
authors.lastname: Matsuoka
authors.forename: T
authors.initials: T
authors.lastname: Yanagishita
authors.forename: K J
authors.initials: KJ
authors.lastname: Kako
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D006997:Hypochlorous Acid / Q000494:pharmacology*; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D002132:Calcium Radioisotopes; D006997:Hypochlorous Acid; D006861:Hydrogen Peroxide; D000252:Calcium-Transporting ATPases; D002118:Calcium