Description | he 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 Km and Vmax 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. | en_US |