Calcium enhances in vitro free radical-induced damage to brain synaptosomes, mitochondria, and cultured spinal cord neurons.
Preincubation of rat brain synaptosomes with xanthine and xanthine oxidase (X/XO) in Ca2+-free Krebs buffer resulted in a 27% inhibition of synaptosomal gamma-aminobutyric acid (GABA) uptake. Addition of 1.5 mM CaCl2 increased the inhibition with X/XO to 46%, and inhibition was essentially complete when the calcium ionophore A23187 also was included. In other studies, preincubation of purified rat brain mitochondria with the combination of X/XO and 4 microM CaCl2 produced a significant (38%) decrease in state 3 respiration with glutamate/malate as substrate that was not seen with either X/XO or Ca2+ alone. Similar results were obtained using cultured mouse spinal cord neurons in which incubation with X/XO/ADP/FeCl2 and A23187 produced membrane damage as assessed by a 32% reduction of neuronal Na+, K+-ATPase activity. Neither X/XO/ADP/FeCl2 nor A23187 alone caused detectable inhibition. These results demonstrate the synergistic damaging effect of free radicals and Ca2+ on membrane function. In addition, they suggest that free radical-induced peroxidation of membrane lipid, occurring focally during complete or nearly complete ischemia in vivo, could result in intense cellular perturbation when coupled with increased intracellular Ca2+.
Braughler
J M
JM
Duncan
L A
LA
Goodman
T
T
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000166:cytology* / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D005609:Free Radicals; D008928:Mitochondria / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D010101:Oxygen Consumption; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology*; D013574:Synaptosomes / Q000187:drug effects*; D019820:Xanthine; D014969:Xanthine Oxidase / Q000378:metabolism; D014970:Xanthines / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D005609:Free Radicals; D014970:Xanthines; D019820:Xanthine; D000001:Calcimycin; D005680:gamma-Aminobutyric Acid; D014969:Xanthine Oxidase; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium