Rat Cardiac Cell Physiology: Length-Tension Relationship and Calcium Sensitivity

Benjamin Beran
Marquette University
Milwaukee, WI
Mentor: Dr. Robert Fitts

Cardiovascular disease is a major cause of death in America today.  In 2003, according to the American Heart Association, 71.3 million Americans had some sort of cardiovascular disease resulting in 910,614 deaths (accounting for 37.3% of all deaths in America).  Exercise has long been shown to improve cardiac function and to deter the onset of cardiovascular disease by improving the heart’s capabilities as a pump.  One study has even shown that exercise can not only prevent, but reverse the effects of hypertrophic cardiomyopathy (Konhilas et.al. 2006).  Determining the cellular mechanisms responsible for exercise’s benefits will allow for better prevention and treatment of cardiovascular disease.

This is a pilot study into the physiology of rat cardiac cells (myocytes).  The primary purposes are to develop and perfect methods and to gather control data for future testing.  The Frank-Starling relationship explains that cardiac cells produce varying forces at differing sarcomere lengths.  This is due to the different degrees of overlap between the actin and myosin microfilaments.  Peak force is obtained at optimal overlap, while force decreases at shorter and longer sarcomere lengths.  The optimal length was found to be 2.2 ?m.  Force is also dependent upon the calcium concentration thus a pCa-force curve was determined and used to establish the optimal calcium content for peak force development.  pCa values tested ranged from 4.5 to 7.0.

This study sets the foundation for further experimenting on both whole-heart and isolated cells.  Whole hearts will be tested in a Langendorff apparatus to determine such characteristics as rate of pressure development.  Afterwards, the myocytes will be isolated based on epicardium versus endocardium.  Eventually exercise protocols for both endurance training (treadmill) and resistive training (weight lifting) will be incorporated to test the effects exercise has on the heart and whether different effects are observed between epicardium and endocardium.
 
 

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