A recent study published in the renowned journal Nature revealed how energy is distributed in muscle cells to ensure their proper functioning. The study is entitled “Mitochondrial reticulum for cellular energy distribution in muscle” and was developed by researchers at the National Heart Lung and Blood Institute (NHLBI) and the National Cancer Institute (NCI), both at the National Institutes of Health (NIH) in Bethesda, Maryland.
Muscle movement by itself requires a great amount of energy that needs to be distributed throughout the cell. Therefore, muscle cells contain many mitochondria, organelles considered the powerhouse of cells where the energy for the body is produced in the form of adenosine triphosphate (ATP). Mitochondria convert food, like sugars and fat, into ATP using an electrical voltage across their membranes as an intermediate energy source.
It is generally thought that mitochondria distribute the energy generated to the muscle cells primarily through diffusion across the crowded cell. However, recent genetic evidence indicated that probably a faster and more efficient method is used as diffusion alone cannot achieve the required energy distribution in heart and skeletal muscle cells.
Researchers have now discovered that the distribution of energy in muscle cells is mainly done by the rapid conduction of electrical charges through a large, interconnected network of mitochondria similar to the wire grid that provides power throughout a city.
“The discovery of this mechanism for rapid distribution of energy throughout the muscle cell will change the way scientists think about muscle function and will open up a whole new area to explore in health and disease,” noted the study’s senior author Dr. Robert S. Balaban in a news release.
The team used state-of-the-art imaging technologies, including 3D electron microscopy and super-resolution optical imaging techniques, to study in detail the mitochondria structure, biochemical composition and functioning in mouse skeletal muscle cells. Researchers found that most mitochondria are part of a highly connected network able to conduct electrical charges. In this way, mitochondria are directly connected to each other and can easily distribute the mitochondrial membrane voltage throughout the cell so that ATP can be produced.
“We originally developed these biological imaging methods to explore mechanisms of HIV-1 infection and structural changes in melanoma cells,” said the study’s co-author Dr. Sriram Subramaniam. “It is very satisfying to see how the methods are now useful in a completely different sphere of biology with this interdisciplinary collaboration.”
This finding may help to better understand muscle diseases linked to energy use in the heart and skeletal muscle including muscular dystrophies, inherited disorders characterized by a progressive skeletal muscle weakness that leads to the degeneration of muscle cells and tissues, compromising locomotion. Muscular dystrophies can also affect specific muscles involved in the respiratory function, leading to breathing complications and cardiac problems.
“Structurally, the mitochondria are arranged in such a way that permits the flow of potential energy in the form of the mitochondrial membrane voltage throughout the cell to power ATP production and subsequent muscle contraction, or movement,” explained Dr. Balaban. “These observations solve the problem of how muscle rapidly distributes energy in the cell for movement, (…) The findings also challenge the older model that energy is distributed by the slow diffusion of high-energy molecules through the remarkably dense muscle cell.”
In conclusion, the team revealed for the first time the energy distribution system in muscle cells, and proposed that membrane potential conduction through the mitochondria network is the primary pathway for energy distribution in skeletal muscle. The authors believe that these findings can have implications in the diagnosis and treatment of muscular diseases.