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Titin the Titan

For more than 100 years, a basic physiological tenet has ruled cardiac function: A healthy beating heart will pump out the same amount of blood that it receives. Known as the Frank-Starling Law of the Heart, it is as accepted as gravity and, like gravity, is still not fully understood. Using X-ray diffraction techniques, Thomas Irving from Illinois Tech’s College of Science and Pieter de Tombe from Loyola University Chicago Stritch School of Medicine discovered that the protein titin may play a critical role in the nano-science behind Frank-Starling. Blood enters the heart during its diastolic phase, when cardiac muscle is relaxed and lengthened. As the heart pumps and enters into its systolic phase, the muscle forcefully contracts through the interaction of myosin and actin protein filaments. Titin serves as a kind of elastic band that stores energy when cardiac muscle is stretched and releases energy when the muscle contracts and shortens. Irving and de Tombe learned that the action of titin pulling on the myosin filaments causes changes that ultimately result in increased strength of muscle contraction when muscle is stretched when the heart fills in the diastolic phase.