In a new study published online on September 22, 2014 in PNAS, researchers at the University of Alberta's Faculty of Medicine & Dentistry in Canada have explained how the function of a key protein in the heart changes in heart failure. Heart disease is the number-one killer in the developed world. The end stage of heart disease is heart failure, in which the heart cannot pump enough blood to satisfy the body's needs. Patients become progressively short of breath as the condition worsens, and they also begin to accumulate fluid in the legs and lungs, making it even more difficult to breathe. The molecular structure of the heart muscle changes as heart failure progresses, though scientists cannot always agree on what changes are good or bad. One change that occurs is an increase in "calcium sensitivity." Calcium ions are pumped in and out of the muscle cell with each heartbeat, turning contractions on and off. When the calcium sensitivity increases, contractility increases, but at a price: the relaxation of the heart becomes slower. Both phases of cardiac function are important: impaired contraction leads to systolic heart failure, while impaired relaxation leads to diastolic heart failure. Both types of heart failure are similar in terms of overall prevalence, symptoms, and mortality. Since 1976, medical researchers have known that the heart regulates its calcium sensitivity by phosphorylating a key cardiac protein called troponin I. The troponin complex is made up of three proteins, C, I, and T, which trigger muscle contraction in response to calcium. In heart failure, the phosphate groups are removed from troponin I, but it wasn't known how this caused an increase in calcium sensitivity. Dr.
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