Dawson 2018 Acta Physiol (Oxf)
|Dawson NJ, Lyons SA, Henry DA, Scott GR (2018) Effects of chronic hypoxia on diaphragm function in deer mice native to high altitude. Acta Physiol (Oxf) 223:e13030.|
Abstract: We examined the effects of chronic hypoxia on diaphragm function in high- and low-altitude populations of Peromyscus mice.
Deer mice (P. maniculatus) native to high altitude and congeneric mice native to low altitude (P. leucopus) were born and raised in captivity to adulthood, and were acclimated to normoxia or hypobaric hypoxia (12 or 9 kPa, simulating hypoxia at 4300 m and 7000 m) for 6-8 weeks. We then measured indices of mitochondrial respiration capacity, force production, and fatigue resistance in the diaphragm.
Mitochondrial respiratory capacities (assessed using permeabilized fibres with single or multiple inputs to the electron transport system), citrate synthase activity (a marker of mitochondrial volume), twitch force production, and muscle fatigue resistance increased after exposure to chronic hypoxia in both populations. These changes were not well explained by variation in the fibre-type composition of the muscle. However, there were several differences in diaphragm function in high-altitude mice compared to low-altitude mice. Exposure to a deeper level of hypoxia (9 kPa vs 12 kPa) was needed to elicit increases in mitochondrial respiration rates in highlanders. Chronic hypoxia did not increase the emission of reactive oxygen species from permeabilized fibres in highlanders, in contrast to the pronounced increases that occurred in lowlanders. In general, the diaphragm of high-altitude mice had greater capillary length densities, produced less force in response to stimulation, and had shorter relaxation times. The latter was associated with higher activity of sarcoplasmic reticulum Ca2+ -ATPase (SERCA) activity in the diaphragm of high-altitude mice.
Overall, our work suggests that exposure to chronic hypoxia increases the capacities for mitochondrial respiration, force production, and fatigue resistance of the diaphragm. However, many of these effects are opposed by evolved changes in diaphragm function in high-altitude natives, such that highlanders in chronic hypoxia maintain similar diaphragm function to lowlanders in sea level conditions. This article is protected by copyright. All rights reserved. • Keywords: High-altitude adaptation, Cytochrome c oxidase, Mammals, Mechanics, Muscle contraction, Amplex Red in muscle fibers • Bioblast editor: Kandolf G • O2k-Network Lab: CA Hamilton Scott GR
Labels: MiParea: Respiration, Comparative MiP;environmental MiP
Stress:Hypoxia Organism: Other mammals Tissue;cell: Skeletal muscle Preparation: Permeabilized tissue
Coupling state: LEAK, OXPHOS Pathway: N, CIV, NS HRR: Oxygraph-2k, O2k-Fluorometer