Abstract
Reactive Oxygen Species (ROS) constitute important intracellular signaling molecules. Mitochondria are admitted sources of ROS, especially of superoxide anions through the electron transport chain. Here the mitochondria-targeted ratiometric pericam (RPmt) was used as a superoxide biosensor, by appropriate choice of the excitation wavelength. RPmt was transfected in vivo into mouse muscles. Confocal imaging of isolated muscle fibers reveals spontaneous flashes of RPmt fluorescence. Flashes correspond to increases in superoxide production, as shown by simultaneous recordings of the fluorescence from MitoSox, a mitochondrial superoxide probe. Flashes occur in all subcellular populations of mitochondria. Spatial analysis of the flashes pattern over time revealed that arrays of mitochondria work as well-defined superoxide-production-units. Increase of superoxide production at the muscle fiber level involves recruitment of supplemental units with no increase in per-unit production. Altogether, these results demonstrate that superoxide flashes in muscle fibers correspond to physiological signals linked to mitochondrial metabolism. They also suggest that superoxide, or one of its derivatives, modulates its own production at the mitochondrial level.
Highlights
Reactive oxygen species (ROS) refer to a group of oxygen containing molecules having the capability of reacting with reduced compounds
Spectral properties of these events presented discrepancies with the calcium-dependence of the excitation spectrum provided by Nagai et al [11] and of the spectrum recorded here in transfected skeletal muscle fibers
In 2 cells transfected with RPmt and loaded with Tetramethyl Rhodamine Methyl Ester (TMRM), 4-ChlDZP application failed to inhibit mitochondrial depolarization induced by superoxide flashes. These results show that IMAC is neither involved in physiological superoxide flashes production nor in flashes-induced mitochondrial depolarizations in skeletal muscle
Summary
Reactive oxygen species (ROS) refer to a group of oxygen containing molecules having the capability of reacting with reduced compounds They were once viewed only as harmful molecules involved in disease and aging. Nowadays, this early perception is being replaced by a new concept whereby at low concentration ROS serve a physiological role as signaling molecules, while at high concentration they can damage critical cellular components, inducing cell death. This early perception is being replaced by a new concept whereby at low concentration ROS serve a physiological role as signaling molecules, while at high concentration they can damage critical cellular components, inducing cell death This dual role of ROS is fundamental in skeletal muscle physiology/pathology. Numerous evidences support a role of ROS in several muscle functions, such as force production [3], initiation of adaptative changes in gene expression [4], and regulation of calcium channels, calcium transporters and calcium-sensing proteins [5,6,7]
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