Neurochemical Research, Vol. 21, No. 3, 1996, pp. 299 304 Sensitivity of ATPase-ADPase Activities from Synaptic Plasma Membranes of Rat Forebrain to Lipid Peroxidation in Vitro and the Protective Effect of Vitamin E Marion Vietta, ~ Silvana S. Frassetto, ~ Ana M. O. Battastini, ~ Adriane Bello-Klein, ~ Cleci Moreira, ~ Renato D. Dias, ~ and Joao J. F. Sarkis t,3 (Accepted November 9, 1995) The in vitro effects of membrane lipid peroxidation on ATPase-ADPase activities in synaptic plasma membranes from rat forebrain were investigated. Treatment of synaptic plasma membranes with an oxidant generating system (H202/FC+/ascorbate) resulted in lipid peroxidation and inhi- bition of the enzyme activity. Besides, trolox as a water soluble vitamin E analogue totally pre- vented lipid peroxidation and the inhibition of enzyme activity. These results demonstrate the susceptibility of ATPase-ADPase activities of synaptic plasma membranes to free radicals and suggest that the protective effect against lipid peroxidation by trolox prevents the inhibition of enzyme activity. Thus, inhibition of ATPase-ADPase activities of synaptic plasma membranes in cerebral oxidative stress probably is related to lipid peroxidation in the brain. KEY WORDS: ATPase-ADPase; ATP diphosphohydrolase; free radicals; oxidative stress; synaptic plasma membranes. INTRODUCTION Reactive oxygen species including oxygen free rad- icals are commonly produced in normal cell metabolism. However, excessive production of these reactive species, as in traumatic or ischemia/reperfusion injury, over- whelms the normal cellular defense systems and can pro- duce tissue damage (1). Oxidative stress on the central nervous tissue can produce damage by several mechanisms including in- creases in intracellular free calcium and release of ex- citatory amino acids (1). Thus, cell injury is proposed to Departamento de Bioquimica, Instituto de Bioci~ncias, Universidad6 Federal do Rio Grande do Sul, Rua Sarmento Leite, 500, Porto Ale- gre, RS, Brasil. Fax number: 5551-2271343. 2 Departamento de Fisiologia, Laborat6rio de Fisiologia Cardiovascular, Instituto de Bioci~ncias, Universidade Federal do Rio Grande do Sul, Rua Sarmento Leite, 500, Porto Alegre, RS, Brasil. 3 To whom to address reprint requests. 299 be a manifestation of membrane disruption elicited by the oxidation of polyunsaturated fatty acids of the bi- layer in the well-documented process termed lipid per- oxidation (2). It is also known that free radicals can damage membrane proteins (3,4). Furthermore, it has been proposed that there is a relationship between lipid peroxidation and protein modification and that lipid-de- rived radicals may be responsible for protein damage (5). For some time our group has been interested in a membrane ecto-enzyme denominated ATP diphospho- hydrolase (apyrase, EC 3.6.1.5). In our studies we have demonstrated that ATP and ADP can be degraded to AMP by the action of an ATP diphosphohydrolase ac- tivity in synaptosomal fractions from different sources (6-13). The possible physiological role for this enzyme is to participate in an "enzyme chain" together with a 5'-nucleotidase in the complete hydrolysis of ATP to adenosine in the synaptic cleft during neurotransmission since recent findings have demonstrated that ATP me- 0364-3190/96,0300-0299S0950/0 9 1996PlenumPublishing Corporation