Mitochondria and blood supply of chicken skeletal muscle fibers in ontogenesis.

Skeletal muscles have been studied during ontogenesis to reveal morphological and functional parameters that at most influence the formation of muscles with different levels of oxygen consumption. Development of oxidative red gastrocnemius muscle (RGM) and glycolytic white pectoralis muscle (WPM) has been studied at a period from being 10-day-old chicken embryos until they become 6-month-old chickens. By morphometry, we measured diameter, length, and numerical density of capillaries; muscle fibers diameter; as well as mitochondria's size, density, and volume fraction in muscle fibers. During the post-embryonic period, the blood flow was estimated by hydrogen clearance method. The data obtained were compared to previously published data on O2 consumption rate in fibers being at the same stages of ontogenesis [Microvasc. Res. 60 (2000) 168]. As shown, relationships between the parameters in the muscles studied appear at different ages. They are described by exponential equations with varying slopes. Beginning with the middle stages of embryogenesis, the clear dependency is seen in both types of muscles between O2 consumption rate in a fiber and summarized perimeter of mitochondria at a fiber section. Capillary bed during embryonal period is superfluous. The clear dependency between capillary-to-fiber number ratio and oxygen consumption in fibers becomes apparent in chickens only 10 days after birth, when the fiber diameter amounts to 20 microm. Since that period, redistribution of mitochondria toward the periphery of a fiber takes place, being especially pronounced in RGM. The regularities found between oxygen delivery and consumption systems enable to search for the leading factors of specialization of skeletal muscles in accordance with the level of oxidative metabolism. These factors may be used for calculation and numerical simulation of the parameters of oxygen transport in skeletal muscles.