PubMed Health⌕ Search

Biomedical subjects

C Chinopoulos

Publications and source records attributed to C Chinopoulos.

7 recordsLinked to original sources
PubMed2001

Mitochondria deficient in complex I activity are depolarized by hydrogen peroxide in nerve terminals: relevance to Parkinson's disease.

Deficiency of complex I in the respiratory chain and oxidative stress induced by hydrogen peroxide occur simultaneously in dopaminergic neurones in Parkinson's disease. Here we demonstrate that the membrane potential of in situ mitochondria (Delta Psi m), as measured by the fluorescence change of JC-l (5,5',6,6'-tetrachloro-1,1,3,3'-tetraethylbezimidazolyl-carbocyani ne iodide), collapses when isolated nerve terminals are exposed to hydrogen peroxide (H(2)O(2), 100 and 500 microM) in combination with the inhibition of complex I by rotenone (5 nM-1 microM). H(2)O(2) reduced the activity of complex I by 17%, and the effect of H(2)O(2) and rotenone on the enzyme was found to be additive. A decrease in Delta Psi m induced by H(2)O(2) was significant when the activity of complex I was reduced to a similar extent as found in Parkinson's disease (26%). The loss of Delta Psi m observed in the combined presence of complex I deficiency and H(2)O(2) indicates that when complex I is partially inhibited, mitochondria in nerve terminals become more vulnerable to H(2)O(2)-induced oxidative stress. This mechanism could be crucial in the development of bioenergetic failure in Parkinson's disease.

Animals↗
PubMed2000

Exacerbated responses to oxidative stress by an Na(+) load in isolated nerve terminals: the role of ATP depletion and rise of [Ca(2+)](i).

We have explored the consequences of a [Na(+)](i) load and oxidative stress in isolated nerve terminals. The Na(+) load was achieved by veratridine (5-40 microM), which allows Na(+) entry via a voltage-operated Na(+) channel, and oxidative stress was induced by hydrogen peroxide (0.1-0.5 mM). Remarkably, neither the [Na(+)](i) load nor exposure to H(2)O(2) had any major effect on [Ca(2+)](i), mitochondrial membrane potential (Deltapsim), or ATP level. However, the combination of an Na(+) load and oxidative stress caused ATP depletion, a collapse of Deltapsim, and a progressive deregulation of [Ca(2+)](i) and [Na(+)](i) homeostasis. The decrease in the ATP level was unrelated to an increase in [Ca(2+)](i) and paralleled the rise in [Na(+)](i). The loss of Deltapsim was prevented in the absence of Ca(2+) but unaltered in the presence of cyclosporin A. We conclude that the increased ATP consumption by the Na,K-ATPase that results from a modest [Na(+)](i) load places an additional demand on mitochondria metabolically compromised by an oxidative stress, which are unable to produce a sufficient amount of ATP to fuel the ATP-driven ion pumps. This results in a deregulation of [Na(+)](i) and [Ca(2+)](i), and as a result of the latter, collapse of Deltapsim. The vicious cycle generated in the combined presence of Na(+) load and oxidative stress could be an important factor in the neuronal injury produced by ischemia or excitotoxicity, in which the oxidative insult is superimposed on a disturbed Na(+) homeostasis.

Adenosine Triphosphate↗
PubMed2000

Reversible depolarization of in situ mitochondria by oxidative stress parallels a decrease in NAD(P)H level in nerve terminals.

We have reported recently (Chinopoulos et al., 1999 J. Neurochem. 73, 220 228) that mitochondrial membrane potential (delta(psi)m) in isolated nerve terminals is markedly reduced by H2O2 in the absence of F0F1-ATPase working as a proton pump. Here we demonstrate that delta(psi)m reduced by H2O2 (0.5 mM) in the presence of oligomycin (10 mM), an inhibitor of the F0F1-ATPase, was able to recover by the addition of catalase (2000 U). Similarly, a decrease in the NAD(P)H level due to H2O2 can be reversed by catalase. In addition, H2O2 decreased the ATP level and the [ATP]:[ADP] ratio measured in the presence of oligomycin reflecting an inhibition of glycolysis by H2O2, but this effect was not reversible. The effect of H2O2 on delta(psi)m in the presence of the complex I inhibitor, rotenone, was also unaltered by addition of catalase. These results provide circumstantial evidence for a relationship between the decreased NAD(P)H level and the inability of mitochondria to maintain delta(psi)m during oxidative stress.

Animals↗
PubMed1999

Depolarization of in situ mitochondria due to hydrogen peroxide-induced oxidative stress in nerve terminals: inhibition of alpha-ketoglutarate dehydrogenase.

Mitochondrial membrane potential (delta psi(m)) was determined in intact isolated nerve terminals using the membrane potential-sensitive probe JC-1. Oxidative stress induced by H2O2 (0.1-1 mM) caused only a minor decrease in delta psi(m). When complex I of the respiratory chain was inhibited by rotenone (2 microM), delta psi(m) was unaltered, but on subsequent addition of H2O2, delta psi(m) started to decrease and collapsed during incubation with 0.5 mM H2O2 for 12 min. The ATP level and [ATP]/[ADP] ratio were greatly reduced in the simultaneous presence of rotenone and H2O2. H2O2 also induced a marked reduction in delta psi(m) when added after oligomycin (10 microM), an inhibitor of F0F1-ATPase. H2O2 (0.1 or 0.5 mM) inhibited alpha-ketoglutarate dehydrogenase and decreased the steady-state NAD(P)H level in nerve terminals. It is concluded that there are at least two factors that determine delta psi(m) in the presence of H2O2: (a) The NADH level reduced owing to inhibition of alpha-ketoglutarate dehydrogenase is insufficient to ensure an optimal rate of respiration, which is reflected in a fall of delta psi(m) when the F0F1-ATPase is not functional. (b) The greatly reduced ATP level in the presence of rotenone and H2O2 prevents maintenance of delta psi(m) by F0F1-ATPase. The results indicate that to maintain delta psi(m) in the nerve terminal during H2O2-induced oxidative stress, both complex I and F0F1-ATPase must be functional. Collapse of delta psi(m) could be a critical event in neuronal injury in ischemia or Parkinson's disease when H2O2 is generated in excess and complex I of the respiratory chain is simultaneously impaired.

Animals↗
PubMed1998

Plasma membrane depolarization and disturbed Na+ homeostasis induced by the protonophore carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazon in isolated nerve terminals.

The effect of the protonophore carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazon (FCCP) was studied on the intracellular [Na+], pH, and plasma membrane potential in isolated nerve terminals. FCCP induced a rise of [Na+]i at, and even below, the concentrations (0.025-1 microM) in which it is usually used in intact cells to eliminate Ca2+ uptake by mitochondria. The FCCP-induced increase of [Na+]i correlates with a fall in both the ATP level and the ATP/ADP ratio. In addition, a sudden rise of the intracellular proton concentration ([H+]i) from 83 +/- 0.4 to 124 +/- 0.7 nM was observed on the addition of FCCP (1 microM). Parallel with the rise in [H+]i, an abrupt depolarization was detected, followed by a slower decrease in the plasma membrane potential. Both the extent of the pHi change and the fast depolarization of the plasma membrane were proportional to the proton electrochemical gradient across the plasma membrane; when this gradient was increased, greater depolarization was detected. The slower decrease of the membrane potential after the fast initial depolarization was abolished when the medium contained no Na+. It is concluded that FCCP (1) gives rise to a depolarization by setting the plasma membrane potential close to the proton equilibrium potential and (2) enhances the intracellular [Na+] as a consequence of an insufficient ATP level and ATP/ADP ratio to fuel the Na+,K+/ATPase. Because both disturbed Na+ homeostasis and plasma membrane depolarization could profoundly interfere with Ca2+ homeostasis in the presence of protonophores, consideration given to these alterations may help to clarify the cellular Ca2+ sequestration processes.

Animals↗
PubMed1997

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.

Adenosine Diphosphate↗