Y W Xie1, M S Wolin. 1. Department of Physiology, New York Medical College, Valhalla 10595, USA.
Abstract
BACKGROUND: Nitric oxide (NO); superoxide anion (O2.d-); the reaction product of NO with O2.d-, peroxynitrite (ONOO-); and ischemia/reperfusion have all been reported to inhibit respiration in isolated mitochondria. However, the specific species involved in the inhibition of respiration in intact tissues are poorly understood. METHODS AND RESULTS: O2 consumption in isolated cardiac muscle from bovine calf hearts was quantified by use of a Clark-type electrode. Exogenous and endogenous sources of NO, from S-nitroso-N-acetylpenicillamine (SNAP) and bradykinin or carbachol, reversibly inhibited respiration, whereas the O2.- releasing agent, pyrogallol (PG), inhibited respiration in a manner that was only partially reversed when examined 15 minutes after the removal of PG. The generation of ONOO- with SNAP + PG caused a potentiation of the O2(-)-elicited inhibition of respiration when examined 15 minutes after the removal of the ONOO- generating system. Tiron (a scavenger of O2.-) did not alter the actions of SNAP, but it attenuated the direct inhibitory effects of PG +/- SNAP and essentially eliminated the suppression of respiration observed 15 minutes after removal of the O2.- or ONOO- generating system. Urate (a scavenger of ONOO-) antagonized only the actions of PG + SNAP. After exposure of muscle slices to a model of hypoxia (15 minutes) and reoxygenation (10 minutes), respiratory inhibition was observed. This reoxygenation-induced inhibition was potentiated by L-arginine, the substrate for NO biosynthesis, and was markedly blocked by nitro-L-arginine (an NO synthase inhibitor), Tiron, or urate. CONCLUSIONS: The potentially physiological reversible regulation of respiration in cardiac muscle by NO is converted to an effect that does not show rapid reversibility under conditions in which ONOO- forms, and this could contribute to cardiac dysfunction in situations such as hypoxia/reoxygenation.
BACKGROUND:Nitric oxide (NO); superoxide anion (O2.d-); the reaction product of NO with O2.d-, peroxynitrite (ONOO-); and ischemia/reperfusion have all been reported to inhibit respiration in isolated mitochondria. However, the specific species involved in the inhibition of respiration in intact tissues are poorly understood. METHODS AND RESULTS:O2 consumption in isolated cardiac muscle from bovinecalf hearts was quantified by use of a Clark-type electrode. Exogenous and endogenous sources of NO, from S-nitroso-N-acetylpenicillamine (SNAP) and bradykinin or carbachol, reversibly inhibited respiration, whereas the O2.- releasing agent, pyrogallol (PG), inhibited respiration in a manner that was only partially reversed when examined 15 minutes after the removal of PG. The generation of ONOO- with SNAP + PG caused a potentiation of the O2(-)-elicited inhibition of respiration when examined 15 minutes after the removal of the ONOO- generating system. Tiron (a scavenger of O2.-) did not alter the actions of SNAP, but it attenuated the direct inhibitory effects of PG +/- SNAP and essentially eliminated the suppression of respiration observed 15 minutes after removal of the O2.- or ONOO- generating system. Urate (a scavenger of ONOO-) antagonized only the actions of PG +SNAP. After exposure of muscle slices to a model of hypoxia (15 minutes) and reoxygenation (10 minutes), respiratory inhibition was observed. This reoxygenation-induced inhibition was potentiated by L-arginine, the substrate for NO biosynthesis, and was markedly blocked by nitro-L-arginine (an NO synthase inhibitor), Tiron, or urate. CONCLUSIONS: The potentially physiological reversible regulation of respiration in cardiac muscle by NO is converted to an effect that does not show rapid reversibility under conditions in which ONOO- forms, and this could contribute to cardiac dysfunction in situations such as hypoxia/reoxygenation.