THE EFFECT OF OXIDATIVE STRESS ON LEVELS OF CYTOSOLIC CALCIUM WITHIN AND UPTAKE OF CALCIUM BY SYNAPTOSOMES

The ability of synaptosomes subjected to oxidative stress, to maintain homeostasis has been evaluated using various indices of cellular integrity. These include levels of cytosolic calcium and leakiness of the plasma membrane. The status of a neural characteristic; depolarization-induced calcium entry into the cytoplasm, has also been studied. The presence of 5 μM FeSO4 and 0.1 mM ascorbic acid increased peroxidative activity as judged by the rate of thiobarbituric acid reactive material production, and depressed levels of free ionic calcium [Ca2+]i as determined using the calcium-sensitive flouorescent indicator dye fura-2. Depolarization-induced influx of 45Ca2+ was greatly depressed under these conditions, while basal calcium uptake was inhibited to a much lesser degree. The efflux of fura-2 from synaptosomes was enhanced in the oxidizing environment, suggesting increased permeability of the synaptosomal outer limiting membrane. The treatment of synaptosomes with 25 μM α-tocopherol succinate before and during exposure to the Fe2+/ascorbate mixture prevented many of the changes otherwise induced by the oxidizing system. Similar pretreatment with β-carotene or superoxide dismutase did not have any protective effect. Ganglioside GM1 pre-exposure did not alter the Fe2+/ascorbate-induced changes in calcium-related parameters, but mitigated synaptosomal plasma membrane damage as judged by fura-2 leakage. Thus exogenous agents may be capable of reducing the severity of oxidative stress in nervous tissue. © 1990.