Lipoxygenase-induced lipid peroxidation of isolated cardiac microsomes modulates their calcium-transporting function

Abstract

We demonstrated previously that products of linoleic and arachidonic acids, arising from enzymatic or non-enzymatic oxidation, inhibit ATP-dependent calcium accumulation into and promote release of calcium from vesicles derived from sarcoplasmic reticulum of guinea-pig heart. In the present study, direct enzymatic peroxidation of cardiac membrane lipids was performed and the effect on calcium transport was examined. Vesicles were preincubated at 37°C with soybean lipoxygenase-1 (linoleate:oxygen oxidoreductase, EC 1.13.11.12) for up to l h prior to the initiation of calcium accumulation. The extent of membrane peroxidation was assessed by monitoring the production of malondialdehyde. Pretreatment of vesicles with lipoxygenase for 40 and 60 min markedly depressed calcium accumulation. The lipoxygenase-induced suppression of calcium transport was completely antagonized by nordihydroguaiaretic acid (1 μM), not at all by indomethacin (1 μM), and only partially by 5,8,11,14-eicosatetraynoic acid (0.3 μM). Low concentrations of calcium (10 −5-5 · 10 −5 M) enhanced, and a high concentration (10 −3 M) inhibited lipoxygenase-induced peroxidation of membrane lipids. The calcium-accumulating ability of the vesicles was inversely related to the extent of membrane peroxidation. The vesicles which showed the highest degree of peroxidation in the presence of 5 · 10 −5 M calcium, accumulated the lowest amount of calcium. In contrast, calcium at 10 −3 M suppressed lipid peroxidation, resulting in higher calcium uptake than in vesicles peroxidized in the absence of calcium. Thus, calcium transport is depressed in microsomes undergoing lipoxygenase-induced peroxidation, a process which in turn is modulated by calcium.