Peroxynitrate formed by mitochondrial NO synthase promotes mitochondrial Ca2+ release

Mitochondria contribute to the maintenance of the intracellular Ca2+ homeostasis by taking up and releasing the cation via separate and specific pathways. The molecular details of the release pathway are elusive but its stimulation by the cross-linking of some vicinal thiols and consequently NAD(+) hydrolysis are known. Thiol cross-linking and NAD(+) hydrolysis can be achieved by addition of peroxynitrite (ONOO-), the product of the reaction between superoxide (O-2(-)) and nitric oxide (nitrogen monoxide, NO.) to mitochondria. Mitochondria contain an NO synthase (mtNOS), which is stimulated by Ca2+, and are a copious source of O-2(-). We show here that intramitochondrially formed ONOO- stimulates the specific, NAD(+)-linked Ca2+ release from mitochondria. Our findings that upon Ca2+ uptake mtNOS is stimulated, that ONOO- is formed, and that Ca2+ is subsequently released from intact mitochondria suggest the existence of a feedback loop, which prevents overloading of mitochondria with Ca2+. (C) 2000 Elsevier Science Inc.