Enhanced depolarization-evoked calcium signal and reduced [ATP]/[ADP] ratio are unrelated events induced by oxidative stress in synaptosomes.
Oxidative insult elicited by hydrogen peroxide (H2O2) was previously shown to increase the basal intracellular Ca2+ concentration in synaptosomes. In the present study, the effect of H2O2 on the depolarization-evoked [Ca2+] signal was investigated. Pretreatment of synaptosomes with H2O2 (0.1-1 mM) augmented the [Ca2+] rise elicited by high K+ depolarization with essentially two alterations, the sudden sharp rise of [Ca2+]i due to K+ depolarization is enhanced and, instead of a decrease to a stable plateau, a slow, steady rise of [Ca2+]i follows the peak [Ca2+]i. H2O2 in the same concentration range lowered the ATP level and the [ATP]/[ADP] ratio. When carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) (1 microM) or rotenone (2 microM)/oligomycin (10 microM) was applied initially to block mitochondrial ATP production, the lowered [ATP]/[ADP] ratio was further reduced by subsequent addition of 0.5 mM H2O2. The decline of the [ATP]/[ADP] ratio was parallel with but could not explain the enhanced K+-evoked [Ca2+]i signal, indicated by experiments in which the [ATP]/[ADP] ratio was decreased by FCCP (0.1 microM) or rotenone (2 microM) to a similar value as by H2O2 without causing any alteration in the [Ca2+]i signal. These results indicate that H2O2-evoked oxidative stress, in its early phase, gives rise to a complex dysfunction in the Ca2+ homeostasis and, parallel with it, to an impaired energy status.
Tretter
L
L
Department of Medical Biochemistry, Semmelweis University of Medicine, Budapest, Hungary.
Chinopoulos
C
C
Adam-Vizi
V
V
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D004734:Energy Metabolism / Q000187:drug effects; D006168:Guinea Pigs; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism / Q000502:physiology*
D016877:Oxidants; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D011188:Potassium; D002118:Calcium