LIPID-PEROXIDATION BOTH INHIBITS CA2-ATPASE AND INCREASES CA2+ PERMEABILITY OF ENDOPLASMIC-RETICULUM MEMBRANE()

Incubation of reticular membranes with Fe2+-EDTA and H2O2 plus Fe2+-ED TA at 37 degrees C for 30 min. led to the loss of membrane's efficienc y to sequester Ca2+ to 21.8 % and 3.6 % of control values, respectivel y. The incubation of microsomes with Fe2+-EDTA and H2O2 plus Fe2+-EDTA also caused decrease of Ca2+-ATPase activity; to 44.9 % and 44.4 % (m easured under the same conditions as Ca2+-uptake) or to 79.6 % and 62. 1 % (uncoupled from Ca2+ transport by detergent). In addition, incubat ion of membranes with Fe2+-EDTA and H2O2 plus Fe2+-EDTA at 37 degrees C for 30 min. led to the increase of Ca2+ permeability to 125.1 % and 124.2 %, respectively. Preincubation of membranes with membrane-solubl e antioxidants (U-74500A, U-83836E, t-butyl hydroxytoluene and stobadi ne) protected the reticular membranes against depression of Ca2+ uptak e values and Ca2+-ATPase inhibition in a dose and an antioxidant natur e dependent manner. Our results indicate that both processes, Ca2+-ATP ase inhibition and increase of endoplasmic reticulum membrane Ca2+ per meability, participate in the lipid peroxidation induced loss of membr ane's efficiency to sequester Ca2+.