Metabolic enzyme activities across an altitudinal gradient: an examination of pikas (genusOchotona)

Abstract

Changes in metabolic enzyme activities were examined in three species of pikas that occur over a range of altitudes. Because these closely related mammals live in comparable ecosystems and face similar environmental factors regardless of altitude, modifications of metabolic machinery are probably due to differences in oxygen availability. Citrate synthase (CS), β-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH) activities were measured in heart, diaphragm, vastus lateralis, gastrocnemius and soleus muscles. Additionally, the activity levels of both M-LDH (skeletal muscle type) and H-LDH (heart type) isozymes were quantified in tissue samples. Pikas from high altitude had greater CS and HOAD activities in heart and diaphragm when compared with pikas from low altitude, while activity levels did not differ in skeletal muscles. The increase in oxidative enzyme activities in tissues with high metabolic demand is thought to enhance oxygen utilization when oxygen availability is low and may reflect greater metabolic demand on heart and diaphragm tissue. Pikas from high altitude were also found to have greater total LDH activities in all tissues examined. High altitude animals had dramatically higher H-LDH activity (2.3-3.8 times greater) while M-LDH activity was more comparable (1.8 times lower to 1.7 times greater) when compared with low altitude animals. High total LDH activity enables pikas to perform short bouts of anaerobic activity, while high levels of H-LDH isozymes may serve to enhance lactate removal and decrease recovery time in animals living at high altitude.

Mitochondrial physiology in the skeletal and cardiac muscles is altered in torrent ducks, Merganetta armata, from high altitudes in the Andes

“…This could act in concert with the greater HOAD activity of highland torrent ducks (Fig. 3), an observation that is consistent with findings in several other high-altitude taxa (Bigard et al, 1991;Léon-Velarde, 1993;Sheafor, 2003;Scott et al, 2009a,b), in order to increase the sustainable yield of ATP from β-oxidation. The heightened activity of CK in the heart of highland torrent ducks might be important for facilitating energy supply.…”

“…It is also possible that the larger relative excess of CIV activity in highland ducks helps increase the O 2 affinity of mitochondria, by reducing the catalytic turnover rate of each CIV enzyme (Gnaiger et al, 1998;Kudin et al, 2002), and thus helps sustain ATP synthesis in hypoxia. However, although unique specializations in the activity, structure and function of CIV have been observed in the locomotor muscles of several high-altitude taxa (Sheafor, 2003;Scott et al, 2011;Lui et al, 2015), it is not clear whether these specializations affect mitochondrial O 2 affinity (Scott et al, 2009a,b).…”

Development of aerobic and anaerobic metabolism in cardiac and skeletal muscles from harp and hooded seals

“…Because cardiac and skeletal muscles respond differently to hypoxic and endurance exercise challenges (Daneshrad et al, 2000;Kainulainen et al, 1984;Ohtsuka and Gilbert, 1995;Sheafor, 2003;Winder et al, 1974;Zonderland et al, 1999), it is possible to speculate about the relative importance of these two stimuli on final tissue maturation. In general, endurance exercise causes much larger increases in CS, HOAD, MT density, Mb and lipid stores than in the glycolytic potential of skeletal muscle, but has little to no impact on these parameters in the heart (Brooks et al, 2005;Driedzic et al, 1987;Stanley et al, 2005;Zonderland et al, 1999).…”

On the generality of a climate-mediated shift in the distribution of the American pika (Ochotona princeps)

“…The American pika is a small, herbivorous lagomorph that resides primarily in talus (rocky debris) found in mountain ranges and high plateaus of western North America. Pikas worldwide benefit from metabolic and behavioral adaptations allowing them to survive cold winters without hibernating (Li et al 2001, Sheafor 2003. However, because their resting body temperature is only a few degrees below lethal body temperature (Li et al 2001), pikas are sensitive to temperature extremes.…”