title: Protein Kinase A Governs Oxidative Phosphorylation Kinetics and Oxidant Emitting Potential at Complex I.
abstract: The mitochondrial electron transport system (ETS) is responsible for setting and maintaining both the energy and redox charges throughout the cell. Reversible phosphorylation of mitochondrial proteins, particularly via the soluble adenylyl cyclase (sAC)/cyclic AMP (cAMP)/Protein kinase A (PKA) axis, has recently been revealed as a potential mechanism regulating the ETS. However, the governance of cAMP/PKA signaling and its implications on ETS function are incompletely understood. In contrast to prior reports using exogenous bicarbonate, we provide evidence that endogenous CO2 produced by increased tricarboxylic acid (TCA) cycle flux is insufficient to increase mitochondrial cAMP levels, and that exogenous addition of membrane permeant 8Br-cAMP does not enhance mitochondrial respiratory capacity. We also report important non-specific effects of commonly used inhibitors of sAC which preclude their use in studies of mitochondrial function. In isolated liver mitochondria, inhibition of PKA reduced complex I-, but not complex II-supported respiratory capacity. In permeabilized myofibers, inhibition of PKA lowered both the K m and V max for complex I-supported respiration as well as succinate-supported H2O2 emitting potential. In summary, the data provided here improve our understanding of how mitochondrial cAMP production is regulated, illustrate a need for better tools to examine the impact of sAC activity on mitochondrial biology, and suggest that cAMP/PKA signaling contributes to the governance of electron flow through complex I of the ETS.
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Kinesiology, East Carolina University Greenville, NC, USA.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Lark
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Physiology, Brody School of Medicine, East Carolina University Greenville, NC, USA.
authors.forename: Lauren R
authors.initials: LR
authors.lastname: Reese
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Physiology, Brody School of Medicine, East Carolina University Greenville, NC, USA.
authors.forename: Terence E
authors.initials: TE
authors.lastname: Ryan
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Kinesiology, East Carolina University Greenville, NC, USA.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Torres
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Physiology, Brody School of Medicine, East Carolina University Greenville, NC, USA.
authors.forename: Cody D
authors.initials: CD
authors.lastname: Smith
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Physiology, Brody School of Medicine, East Carolina University Greenville, NC, USA.
authors.forename: Chien-Te
authors.initials: CT
authors.lastname: Lin
authors.affiliation: East Carolina Diabetes and Obesity Institute Greenville, NC, USA ; Department of Kinesiology, East Carolina University Greenville, NC, USA ; Department of Physiology, Brody School of Medicine, East Carolina University Greenville, NC, USA.
authors.forename: P Darrell
authors.initials: PD
authors.lastname: Neufer
keywords: adenylyl cyclase; cAMP; complex I; liver; mitochondria; protein kinase A; respiration; skeletal muscle