Quinone imine-induced Ca 2+ release from isolated rat liver mitochondria

Abstract

Incubation of Ca 2+-loaded rat liver mitochondria with N-acetyl- p-benzoquinone imine (NAPQI) or its two dimethylated analogues resulted in a concentration dependent Ca 2+ release, with the following order of potency: 2,6-(Me) 2-NAPQI>NAPQI> 3,5-(Me) 2-NAPQI. The quinone imine-induced Ca 2+ release was associated with NAD(P)H oxidation and was prevented when NAD(P) + reduction was stimulated by the addition of 3-hydroxybutyrate. Mitochondrial glutathione was completely depleted within 0.5 min by all three quinone imines, even at low concentrations that did not result in Ca 2+ release. Depletion of mitochondrial GSH by pretreatment with 1-chloro-2,4-dinitrobenzene enhanced quinone imine-induced NAD(P)H oxidation and Ca 2+ release. However, 3-hydroxybutyrate protected from quinone imine-induced Ca 2+ release in GSH-depleted mitochondria. Mitochondrial membrane potential was lost after the addition of quinone imines at concentrations that caused rapid Ca 2+ release; however, subsequent addition of EGTA led to the complete recovery of the transmembrane potential. In the absence of Ca 2+, the quinone imines caused only a small and transient loss of the transmembrane potential. Taken together, our results suggests that the quinone imine-induced Ca 2+ release from mitochondria is a consequence of NAD(P)H oxidation rather than GSH depletion, GSSG formation, or mitochondrial inner membrane damage.