Ascorbate‐Induced Lipid Peroxidation and Inhibition of [3H]Spiroperidol Binding in Neostriatal Membrane Preparations

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Abstract
Sodium ascorbate caused an increased lipid peroxidation and a large decrement in [3H]spiroperidol binding in a rat neostriatal membrane preparation (preparation C). Both effects were greater at intermediate (0.05 and 0.5 mM) than at higher or lower ascorbate concentrations. In another neostriatal membrane preparation (preparation A), there was no loss of [3H]spiroperidol binding and only a small increase in lipid peroxidation caused by ascorbate. Both the ascorbate-induced increase in lipid peroxidation and loss of [3H]spiroperidol binding were greatly enhanced in preparation A by the addition of Fe salts. In experiments designed to explore reasons for these apparent discrepancies, the method of tissue preparation was a critical factor. The ascorbate effects were consistently greater in a tissue preparation which was originally homogenized in an isotonic sucrose medium and centrifuged, and the cell debris discarded (as was done in preparation C), than in one in which the tissue was homogenized in a hypotonic medium and in which no low-speed centrifugation was done (as was done in preparation A). In other experiments, of several cations tested, only ferrous and ferric ions potentiated the above-described effects of ascorbate. Some ascorbic acid derivatives (e.g., isoascorbic acid) had properties similar to those of ascorbic acid, whereas several reducing agents could, in the presence of added Fe salts, cause both a lipid peroxidation and a loss of [3H]spiroperidol binding. The other reducing agents tested (e.g., dithiothreitol) were less potent in both regards than was ascorbate. In other experiments, several chelating agents (e.g., EDTA) or commonly used inhibitors of lipid peroxidation (e.g., propyl gallate) were able to counteract the effects of ascorbate on lipid peroxidation and on [3H]spiroperidol binding.