title: Mitochondrial Ca2+-induced K+ influx increases respiration and enhances ROS production while maintaining membrane potential.
abstract: We recently demonstrated a role for altered mitochondrial bioenergetics and reactive oxygen species (ROS) production in mitochondrial Ca(2+)-sensitive K(+) (mtK(Ca)) channel opening-induced preconditioning in isolated hearts. However, the underlying mitochondrial mechanism by which mtK(Ca) channel opening causes ROS production to trigger preconditioning is unknown. We hypothesized that submaximal mitochondrial K(+) influx causes ROS production as a result of enhanced electron flow at a fully charged membrane potential (DeltaPsi(m)). To test this hypothesis, we measured effects of NS-1619, a putative mtK(Ca) channel opener, and valinomycin, a K(+) ionophore, on mitochondrial respiration, DeltaPsi(m), and ROS generation in guinea pig heart mitochondria. NS-1619 (30 microM) increased state 2 and 4 respiration by 5.2 +/- 0.9 and 7.3 +/- 0.9 nmol O(2).min(-1).mg protein(-1), respectively, with the NADH-linked substrate pyruvate and by 7.5 +/- 1.4 and 11.6 +/- 2.9 nmol O(2).min(-1).mg protein(-1), respectively, with the FADH(2)-linked substrate succinate (+ rotenone); these effects were abolished by the mtK(Ca) channel blocker paxilline. DeltaPsi(m) was not decreased by 10-30 microM NS-1619 with either substrate, but H(2)O(2) release was increased by 44.8% (65.9 +/- 2.7% by 30 muM NS-1619 vs. 21.1 +/- 3.8% for time controls) with succinate + rotenone. In contrast, NS-1619 did not increase H(2)O(2) release with pyruvate. Similar results were found for lower concentrations of valinomycin. The increase in ROS production in succinate + rotenone-supported mitochondria resulted from a fully maintained DeltaPsi(m), despite increased respiration, a condition that is capable of allowing increased electron leak. We propose that mild matrix K(+) influx during states 2 and 4 increases mitochondrial respiration while maintaining DeltaPsi(m); this allows singlet electron uptake by O(2) and ROS generation.
authors.affiliation: Anesthesiology Research Laboratories, Department of Anesthesiology, Medical College of Wisconsin, M4280, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
authors.forename: André
authors.initials: A
authors.lastname: Heinen
authors.forename: Amadou K S
authors.initials: AK
authors.lastname: Camara
authors.forename: Mohammed
authors.initials: M
authors.lastname: Aldakkak
authors.forename: Samhita S
authors.initials: SS
authors.lastname: Rhodes
authors.forename: Matthias L
authors.initials: ML
authors.lastname: Riess
authors.forename: David F
authors.initials: DF
authors.lastname: Stowe
mesh_terms: D000818:Animals; D005260:Female; D006168:Guinea Pigs; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D008929:Mitochondria, Heart / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D007476:Ionophores; D024681:Potassium Channels, Calcium-Activated; D017382:Reactive Oxygen Species; D014634:Valinomycin; D011188:Potassium