Muscle Cells Run Out of Gas
Posted April 1, 1998
Inside each human cell are the mitochondria that power nearly all of the cell's activity. Mitochondria contain their own DNA with genes that code for proteins important
in the function of the mitochondria. Scientists have known for many years that defects in nuclear DNA can cause various genetic diseases. Now, defects in the genes of mitochondria have
also been found to cause human genetic diseases. A rare form of blindness and one form of non-insulin dependent diabetes have been demonstrated to result from mutations in mitochondrial
DNA.
Dr. Douglas C. Wallace, at the Emory University School of Medicine, recently found that defects in mitochondrial DNA can cause heart and skeletal muscle problems
in mice. His research team has studied a mitochondrial gene that codes for a protein found in the membrane of mitochondria called ANT1. This protein is a translocator protein for adenine
nucleotides. This protein acts like the gas pump hose at the gas station. When the hose works, gas flows through it and can enter your car's gas tank. If the hose malfunctions, gas cannot
leave the gas pump or flow through it.
Like gasoline, ATP must be pumped out of heart and skeletal muscle mitochondria using the mouse's ANT1 translocator protein. Wallace's team disabled the gene for
this protein in mice. Upon examining the mouse skeletal muscle cells, they found abnormal mitochondria. The mitochondria had a bloated appearance and had multiplied, displacing the contractile
machinery in the muscle cell. Even though the mitochondria could still make ATP, they could not move the ATP out into the cytoplasm of the muscle cell. The heart muscle cells also showed
a large increase in mitochondria, although these were not bloated. The researchers hypothesize this was because cardiac cells contain a second type of ATP translocator.
When normal and mutant mice were exercised on a treadmill, the normal mice had no trouble completing a 25-minute test. None of the genetically altered mice (with nonfunctioning
ANT1 protein) could complete the test, suggesting the abnormal muscle cell mitochondria could not keep up with the exercise demands for energy (ATP). The scientists hypothesize that
in humans, damaged mitochondria may play a role in muscle fatigue, heart failure, memory loss and even aging.
References
Fackelmann, Kathleen. "Power Failure: What happens when muscle cells run out of fuel," Science News, Vol. 152, September 27, 1997, pp. 206-207.
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