title: Reverse electron flow-induced ROS production is attenuated by activation of mitochondrial Ca2+-sensitive K+ channels.
abstract: Mitochondria generate reactive oxygen species (ROS) dependent on substrate conditions, O(2) concentration, redox state, and activity of the mitochondrial complexes. It is well known that the FADH(2)-linked substrate succinate induces reverse electron flow to complex I of the electron transport chain and that this process generates superoxide (O(2)(*-)); these effects are blocked by the complex I blocker rotenone. We demonstrated recently that succinate + rotenone-dependent H(2)O(2) production in isolated mitochondria increased mildly on activation of the putative big mitochondrial Ca(2+)-sensitive K(+) channel (mtBK(Ca)) by low concentrations of 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619). In the present study we examined effects of NS-1619 on mitochondrial O(2) consumption, membrane potential (DeltaPsi(m)), H(2)O(2) release rates, and redox state in isolated guinea pig heart mitochondria respiring on succinate but without rotenone. NS-1619 (30 microM) increased state 2 and state 4 respiration by 26 +/- 4% and 14 +/- 4%, respectively; this increase was abolished by the BK(Ca) channel blocker paxilline (5 microM). Paxilline alone had no effect on respiration. NS-1619 did not alter DeltaPsi(m) or redox state but decreased H(2)O(2) production by 73% vs. control; this effect was incompletely inhibited by paxilline. We conclude that under substrate conditions that allow reverse electron flow, matrix K(+) influx through mtBK(Ca) channels reduces mitochondrial H(2)O(2) production by accelerating forward electron flow. Our prior study showed that NS-1619 induced an increase in H(2)O(2) production with blocked reverse electron flow. The present results suggest that NS-1619-induced matrix K(+) influx increases forward electron flow despite the high reverse electron flow, and emphasize the importance of substrate conditions on interpretation of effects on mitochondrial bioenergetics.
authors.affiliation: Anesthesiology Research Laboratories, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: André
authors.initials: A
authors.lastname: Heinen
authors.forename: Mohammed
authors.initials: M
authors.lastname: Aldakkak
authors.forename: David F
authors.initials: DF
authors.lastname: Stowe
authors.forename: Samhita S
authors.initials: SS
authors.lastname: Rhodes
authors.forename: Matthias L
authors.initials: ML
authors.lastname: Riess
authors.forename: Srinivasan G
authors.initials: SG
authors.lastname: Varadarajan
authors.forename: Amadou K S
authors.initials: AK
authors.lastname: Camara
mesh_terms: D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D006861:Hydrogen Peroxide / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008929:Mitochondria, Heart / Q000378:metabolism*; D010084:Oxidation-Reduction; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D001562:Benzimidazoles; D007211:Indoles; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D017382:Reactive Oxygen Species; C086491:NS 1619; C048220:paxilline; D006861:Hydrogen Peroxide; D011188:Potassium