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A relaxed state of myosin may relax the heart

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New studies have expanded the horizons of our understanding of the heart muscle and its functions to such an extent that the new findings may even help in preserving organs for transplantation for much longer than was earlier possible. According to research published in the Journal of Biophysics, a relaxed state of the cardiac muscle has been discovered in which the metabolism rate is very slow. This relaxed state can be harnessed to fine tune the use of precious body energy in emergency situations.

Muscle cells are a type of specialized cells which contract when force is applied on them. This force generated in a muscle cell comes from a variety of sources depending on the type of the muscle cell. Calcium being one of the main ingredients acts as a trigger for muscle contraction. Nevertheless, newer research has thrown some light on the role of myosin, a motor protein that mediates contraction of a muscle. When the contractile proteins myosin and actin bind to each other, physical shortening of the muscle fibre takes place by the utilization of ATP stored in it.

Dr Roger Cooke from the University of California, San Francisco said that his team detected the presence of a ‘super relaxed’ state of the contractile protein myosin in a skeletal muscle cell, which has been named SRX. According to Dr Roger Cooke, this super relaxed state has a relatively smaller ATP turnover as well as lower energy utilization. If we consider the crude example of a car’s engine the active state of myosin is comparable to that of a car running at full throttle while a normal relaxed state corresponds to a car stopped at a traffic signal but with the engine still on. The SRX state, on the other hand, matches up with a car in a parking lodge with its engine switched off. In the current study, the research is based on cardiac muscle instead of the existing study on the presence of SRX in a skeletal muscle.

Laborious studies by Dr Cooke and his colleagues have revealed that a super relaxed state similar to SRX exists in the cardiac muscle as well. However, the active state of a cardiac muscle and a skeletal muscle are incomparable. While a skeletal muscle does not retain the super relaxed state for long, a cardiac muscle on the contrary maintains its SRX state. This implies that the role of SRX differs for cardiac and skeletal muscle.

As revealed by Dr Roger Cooke, the state of myosin in a cardiac muscle has a very low turnover rate as compared to that of a skeletal muscle. Experts predict that this low turnover rate could be used to relieve the myocardium of the heart in times of extreme stress. If the SRX state can be artificially induced, it can help protect the heart from suffering critical damage, like during a heart attack. Another possible implication of the SRX state is for preserving organs for transplantation.

Pleuni Hooijman, Melanie A. Stewart and Roger Cooke. A New State of Cardiac Myosin with Very Slow ATP Turnover: A Potential Cardioprotective Mechanism in the Heart. Biophysical Journal, Volume 100, Issue 8, 1969-1976.
published: 12 Nov 2011 (0:14)

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