My doctor said there was a problem with the "Calcium Handling Failing Heart" in my heart. What does this mean? I thought Ca2+ was in bones. Help!

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Answered by: Jane, An Expert in the Heart Disease - General Category
The body is amazing! While mankind usually builds things that do one thing OR another, the body builds things that are almost always multi-purpose. Take bones, for instance. While it is certainly true that bones are structures rich in calcium and other minerals, it is also true that the body extracts calcium from them when needed by other organs. That's one reason people get osteoporosis—because when the body is low on calcium, it pulls calcium from the bones--where it is essential, but its absence is not immediately life threatening—to deploy it elsewhere.



But where, you may ask? In muscle! It may surprise you, but muscles can NOT contract without calcium: we couldn't walk, talk, sit, stand, digest food, or give birth without it. It is equally true that the heart--the body's most important muscle--can't contract without this mineral. It turns out the there are only two proteins in the entire biosphere that can interact in such a way as to produce motion--actin and myosin. Actin is like the water, and myosin is like the oar.

To continue the analogy, myosin is "locked" on the side of the rowboat until calcium "unlocks" it. Once free, myosin can then use energy in the cell to "row" against actin and cause muscles to shorten—what we call “contraction.” Too much calcium in the heart means it doesn't relax properly; too little and it can't generate enough force to pump blood efficiently throughout the body. This is what your doctor calls a "failing heart." It means the heart has failed to meet the body's metabolic requirements. This is the meaning of "Calcium Handling Failing Heart."



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(Note to editors: The system "forced" me to write slightly more than I wanted to, and add the question at the beginning and the sentence at the end. Apparently it could not skim the paragraph and simply find words that were in the search box. It wanted to see the entire phrase as such. Please take that into consideration when scoring this entry. Thanks!)

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For more information see also:

http://circres.ahajournals.org/cgi/content/abstract/hh1401.093584v1

Ectopic expression of the sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA) 1a pump in the mouse heart results in a 2.5-fold increase in total SERCA pump level. SERCA1a hearts show increased rates of contraction/relaxation and enhanced Ca2+ transients; however, the cellular mechanisms underlying altered Ca2+ handling in SERCA1a transgenic (TG) hearts are unknown. In this study, using confocal microscopy, we demonstrate that SERCA1a protein traffics to the cardiac SR and structurally substitutes for the endogenous SERCA2a isoform. SR Ca2+ load measurements revealed that TG myocytes have significantly enhanced SR Ca2+ load. Confocal line-scan images of field-stimulated SR Ca2+ release showed an increased rate of Ca2+ removal in TG myocytes. On the other hand, ryanodine receptor binding activity was decreased by 30%. However, TG myocytes had a greater rate of spontaneous ryanodine receptor opening as measured by spark frequency. Whole-cell L-type Ca2+ current density was reduced by 50%, whereas the time course of inactivation was unchanged in TG myocytes. These studies provide important evidence that SERCA1a can substitute both structurally and functionally for SERCA2a in the heart and that SERCA1a overexpression can be used to enhance SR Ca2+ transport and cardiac contractility.

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