Skeletal muscle mitoflashes, pH, and the role of uncoupling protein-3.

Mitochondrial reactive oxygen species (ROS) are important cellular signaling molecules, but can cause oxidative damage if not kept within tolerable limits. An important proximal form of ROS in mitochondria is superoxide. Its production is thought to occur in regulated stochastic bursts, but current methods using mitochondrial targeted cpYFP to assess superoxide flashes are confounded by changes in pH. Accordingly, these flashes are generally referred to as 'mitoflashes'. Here we provide regulatory insights into mitoflashes and pH fluctuations in skeletal muscle, and the role of uncoupling protein-3 (UCP3). Using quantitative confocal microscopy of mitoflashes in intact muscle fibers, we show that the mitoflash magnitude significantly correlates with the degree of mitochondrial inner membrane depolarization and ablation of UCP3 did not affect this correlation. We assessed the effects of the absence of UCP3 on mitoflash activity in intact skeletal muscle fibers, and found no effects on mitoflash frequency, amplitude or duration, with a slight reduction in the average size of mitoflashes. We further investigated the regulation of pH flashes (pHlashes, presumably a component of mitoflash) by UCP3 using mitochondrial targeted SypHer (mt-SypHer) in skeletal muscle fibers. The frequency of pHlashes was significantly reduced in the absence of UCP3, without changes in other flash properties. ROS scavenger, tiron, did not alter pHlash frequency in either WT or UCP3KO mice. High resolution respirometry revealed that in the absence of UCP3 there is impaired proton leak and Complex I-driven respiration and maximal coupled respiration. Total cellular production of hydrogen peroxide (H2O2) as detected by Amplex-UltraRed was unaffected. Altogether, we demonstrate a correlation between mitochondrial membrane potential and mitoflash magnitude in skeletal muscle fibers that is independent of UCP3, and a role for UCP3 in the control of pHlash frequency and of proton leak- and Complex I coupled-respiration in skeletal muscle fibers. The differential regulation of mitoflashes and pHlashes by UCP3 and tiron also indicate that the two events, though may be related, are not identical events.

""Non-communicating'' syringomyelia: a non-existent entity.

Encroachment by man's overlarge forebrain is responsible for the anatomic substrate of syringomyelia, i.e. a hindbrain hernia developing in fetal life with persisting hydromyelia. Communication between the syrinx and 4th ventricle is readily disclosed at operation, but because of postmortem shrinkage, almost never at autopsy. Syringomyelia developing in 16 of 864 post-traumatic paraplegics has been classified non-communicating. However, the syrinx, its fluid, and the ultimate clinical picture are the same as in the non-traumatic, and surgical exposure has disclosed the communication. The symptoms develop because the traumatic subarachnoid block exaggerates the causative intracranial fluid pulse waves by eliminating the dampling effect of the yielding dural sac below. A non-traumatic spinal block also may result in syringomyelia.