Research Pinpoints Crucial Protein That Keeps The Heart Beating On Time

The average heart beats 35 million times a year - 2.5 billion times over a lifetime. Those beats must be precisely calibrated; even a small divergence from the metronomic rhythm can cause sudden death. For decades, scientists have wondered exactly how the heart stays so precisely on rhythm even though it contains so many moving parts.
Now, researchers have identified how a particular protein plays a central role in this astonishing consistency. This is the first time the mechanism has been described; the discovery could eventually help scientists treat heart problems that kill millions of people every year. The results appear in the journal Science Advances.
For years, researchers have known that calcium acts as a trigger for the heartbeat, activating proteins that cause the sarcomeres - the fibrous proteins that make up heart muscle cells - to contract. The researchers found that the calcium molecules are not distributed evenly across the length of each sarcomere; the molecules are released from the ends. Despite this, the sarcomeres contract uniformly. But exactly how has remained a thorny mystery.
Now researchers have found the answer: C protein. This protein was known to exist in all heart muscle cells, but until now, its function was unknown. Using an animal model, the researchers studied the physiology of sarcomeres, measuring calcium release and the muscle fibers' mechanical reaction. It turns out that C protein sensitizes certain parts of the sarcomere to calcium. As a result, the middle of the sarcomere contracts just as much as the ends, despite having much less calcium. In other words, C protein enables the sarcomeres to contract synchronously.
C protein appears to play a large part in many forms of heart disease. In the most severe cases, defects in C-protein lead to extremely serious arrhythmias, which cause sudden death when the heart loses the ability to pump blood. In the U.S., arrhythmias contribute to about 300,000 deaths a year, according to the American Heart Association. (Not all arrhythmias are fatal; some can be controlled with medicines and electrical stimulation.)
The researchers believe that it may be possible to affect arrhythmias by modifying the activity of C protein through drugs. However, many many challenges remain in unravelling how C protein mutations produce contractile and arrhythmic dysfunction in disease.

Based on material originally posted by University of Maryland School of Medicine.