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+‐EDTA at 37 °C for 30 min. led to the loss of membrane's efficiency to sequester Ca2+ to 21.8 % and 3.6 % of control values, respectively. 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 % (measured under the same conditions as Ca2+‐uptake) or to 79.6 % and 62.1 % (uncoupled from Ca2+ transport by detergent). In addition, incubation of membranes with Fe2+‐EDTA and H2O2 plus Fe2+‐EDTA at 37 °C for 30 min. led to the increase of Ca2+ permeability to 125.1 % and 124.2 %, respectively. Preincubation of membranes with membrane‐soluble antioxidants (U‐74500A, U‐83836E, t‐butyl hydroxytoluene and stobadine) protected the reticular membranes against depression of Ca2+ uptake values and Ca2+‐ATPase inhibition in a dose and an antioxidant nature dependent manner. Our results indicate that both processes, Ca2+‐ATPase inhibition and increase of endoplasmic reticulum membrane Ca2+ permeability, participate in the lipid peroxidation induced loss of membrane's efficiency to sequester Ca2+.