Biological complexity: circadian muscle oxygen use (Introduction)

by David Turell , Friday, October 21, 2016, 18:37 (2955 days ago) @ David Turell

It is logical to have a way to use oxygen more efficiently in muscles in the daytime when we are active. There is such a mechanism:

https://www.sciencedaily.com/releases/2016/10/161020144129.htm

"Northwestern Medicine scientists have discovered circadian clocks in muscle tissue that control the muscle's metabolic response and energy efficiency depending on the time of day.

"The finding in mice sheds light on the time-of-day differences in muscle's ability to adapt to exercise and use oxygen for energy. Muscle cells are more efficient during an organism's normal waking hours, the study found.

"All cells in the body, including those in muscle, contain a clock that regulates how cells adapt to changes in the environment and activity across the 24-hour day.

"'Oxygen and the internal clock are doing a dance together inside muscle cells to produce energy, and the time of day determines how well that dance is synchronized," said senior author Dr. Joseph Bass. "The capacity for a cell to perform its most important functions, to contract, will vary according to the time of day."

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"In the research, scientists performed studies in mice, which were exercised on a treadmill at different times of day, as well as in isolated muscle fibers in which the circadian clock was genetically mutated.

"The scientists analyzed mouse muscle tissues and muscle fibers for expression of genes that are important for exercise. In this way, they determined the impact of deregulation of the circadian clock on muscle fibers in terms of how muscle processes fuel, like sugar and fat, when oxygen levels are low.

"'When we manipulated the clock genetically, we noticed there were profound abnormalities in the muscle," Bass said. "That set us on a course to understand how the inner muscle clock is important in regulating how well the muscle cell can mobilize energy."

"When mice, which are nocturnal, are exercised during the night, their muscles are better at turning on genes to help them adapt to exercise, scientists found. Since these genes also exist in humans, this suggests humans may also be able to respond better to exercise during the daytime.

"The muscle clocks control the metabolic response by interacting with proteins called HIFs that change metabolism when oxygen concentrations get too low in order to allow muscle cells to continue to make energy.

"Normally when we rest or do low-level exercise, our muscles consume oxygen to make energy. When we start to sprint or exercise strenuously, we consume oxygen faster and quickly run out. That's when the dip in oxygen triggers HIFs and signals muscles to switch to sugar for energy -- which in turn increases lactic acid.

"Turning off the muscle clock prevented the normal capacity of exercise to induce sugar consumption and generation of lactic acid. These findings suggest that better exercise capacity may be tied to specific times of day."

Comment: A very reasonable relationship with day and activity. Another addition to biological complexity which raises the bar much higher for chance development of multicellular biochemical mechanisms.