Skeletal muscle mitochondria: the aerobic gate?
At an animal's maximum aerobic capacity (VO2max), the O2 flowing through the respiratory system is consumed by a functionally exclusive sink, skeletal muscle mitochondria. Thus, O2 consumption will never exceed the muscles O2 demand. If the system is ideally designed, structures upstream to the skeletal muscle O2 sink must be built to insure adequate O2 delivery to the working muscle. There are a number of structure-function solutions available to supply the demanded O2 to the muscle; these have been found to vary, often ontogenetically, with hypoxia, training, etc. But there is one relationship that is invariant: Total O2 uptake can be predicted by the total (active) skeletal muscle mitochondrial volume. In aerobic and sedentary animals, across a range of body sizes, maximum (in vivo) mitochondrial O2 consumption is constant among mammals (at approximately 2000 O2 molecules per square micron of inner mitochondrial membrane per second). Because the volume of mitochondria is one of the most plastic of all respiratory structures, we interpret this relationship as suggesting that skeletal muscle mitochondria alone sets the demand for O2 and, thus, the volume of skeletal muscle mitochondria dictates an animal's maximum aerobic capacity.
Lindstedt
S L
SL
Department of Zoology and Physiology, University of Wyoming, Laramie 82071.
Wells
D J
DJ
D000818:Animals; D006801:Humans; D008931:Mitochondria, Muscle / Q000502:physiology*; D010101:Oxygen Consumption