Skeletal muscle mass and composition during mammalian hibernation.

Hibernation is characterized by prolonged periods of inactivity with concomitantly low nutrient intake, conditions that would typically result in muscle atrophy combined with a loss of oxidative fibers. Yet, hibernators consistently emerge from winter with very little atrophy, frequently accompanied by a slight shift in fiber ratios to more oxidative fiber types. Preservation of muscle morphology is combined with down-regulation of glycolytic pathways and increased reliance on lipid metabolism instead.

High-altitude diving in river otters: coping with combined hypoxic stresses.

River otters (Lontra canadensis) are highly active, semi-aquatic mammals indigenous to a range of elevations and represent an appropriate model for assessing the physiological responses to diving at altitude. In this study, we performed blood gas analyses and compared blood chemistry of river otters from a high-elevation (2357 m) population at Yellowstone Lake with a sea-level population along the Pacific coast. Comparisons of oxygen dissociation curves (ODC) revealed no significant difference in hemoglobin-oxygen (Hb-O(2)) binding affinity between the two populations - potentially because of demands for tissue oxygenation.

Avoidance of skeletal muscle atrophy in spontaneous and facultative hibernators.

Smooth and skeletal muscle changes were compared from overwintering white-tailed prairie dogs, spontaneous hibernators that undergo regular, low-temperature torpor bouts, and black-tailed prairie dogs, facultative hibernators that use sporadic, moderate-temperature torpor bouts. The objectives were to assess the abilities of these two species with dramatically different torpor patterns (1) to conserve skeletal muscle morphology, protein, and strength and (2) to use labile protein in the small intestine and liver during the winter season of reduced activity and food intake. Mass and protein concentration of the extensor digitorum longus (EDL), soleus, liver, and small intestine, as well as skeletal muscle strength and fiber morphology for the EDL and soleus, were compared before and after hibernation in both species.

Maintenance of slow type I myosin protein and mRNA expression in overwintering prairie dogs (Cynomys leucurus and ludovicianus) and black bears (Ursus americanus).

Hibernating mammals have the remarkable ability to withstand long periods of fasting and reduced activity with dramatic maintenance of skeletal muscle function and protein composition. We investigated several hindlimb muscles of white-tailed prairie dogs (Cynomys leucurus) and black bears (Ursus americanus), two very different hibernators who are dormant and fasting during winter. The black-tailed prairie dog (C.