Effect of peroxide, sodium, and calcium on brain mitochondrial respiration in vitro: potential role in cerebral ischemia and reperfusion.
Mitochondrial pyruvate-supported respiration was studied in vitro under conditions known to exist following ischemia, i.e., elevated extramitochondrial Ca2+, Na+, and peroxide. Ca2+ alone (7-10 nmol/mg) decreased state 3 and increased state 4 respiration to 81 and 141% of control values, respectively. Sodium (15 mM) and/or tert-butyl hydroperoxide (tBOOH; up to 2,000 nmol/mg protein) alone had no effect on respiration; however, Na+ or tBOOH in combination with Ca2+ dramatically altered respiration. Respiratory inhibition induced by Ca2+ and tBOOH does not involve pyruvate dehydrogenase (PDH) inhibition since PDH flux increased linearly with tBOOH concentration (R = 0.96). Calcium potentiated tBOOH-induced mitochondrial NAD(P)H oxidation and shifted the redox state of cytochrome b from 67 to 47% reduced. Calcium (5.5 nmol/mg) plus Na+ (15 mM) decreased state 3 and increased state 4 respiratory rates to 55 and 202% of control values, respectively. Sodium- as well as tBOOH-induced state 3 inhibition required mitochondrial Ca2+ uptake because ruthenium red addition before Ca2+ addition negated the effect. The increase in state 4 respiration involved Ca2+ cycling since ruthenium red immediately returned state 4 rates back to control values. The mechanisms for the observed Ca2(+)-, Na(+)-, and tBOOH-induced alterations in pyruvate-supported respiration in vitro are discussed and a multifactorial etiology for mitochondrial respiratory dysfunction following cerebral ischemia in vivo is proposed.
Vlessis
A A
AA
Department of Surgery, Oregon Health Sciences University, Portland 97201.
Widener
L L
LL
Bartos
D
D
D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D002545:Brain Ischemia / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D003573:Cytochrome b Group / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D010545:Peroxides / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D015424:Reperfusion; D012964:Sodium / Q000494:pharmacology*; D020122:tert-Butylhydroperoxide
D003573:Cytochrome b Group; D010545:Peroxides; D009249:NADP; D020122:tert-Butylhydroperoxide; D012964:Sodium; D002118:Calcium