Cedars-Sinai Study Identifies Heart-Specific Protein That Protects Against Arrhythmia

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Embargo: May 18, 2014 at 1 p.m. EDT

Newswise LOS ANGELES (STRICTLY EMBARGOED UNTIL MAY 18, 2014 AT 1 P.M. EDT) Researchers at the Cedars-Sinai Heart Institute have identified a heart-specific form of a protein, BIN1, responsible for sculpting tiny folds in pockets that are present on the surface of heart muscle cells. The study provides the first direct evidence of a previously theoretical fuzzy space or slow diffusion zone that protects against irregular heartbeats by maintaining an ideal concentration of electrochemical molecules.

The findings help us understand how heart cells are organized, but more importantly, they give us insight into the way heart cells change when hearts start to fail, said Robin Shaw, MD, PhD, cardiologist and expert in heart failure and rhythm abnormalities at the Heart Institute.

In addition, the results have diagnostic implications and eventually could lead to therapeutic options, said Shaw, senior author of an article in the May 18 issue of Nature Medicine that describes the study, which was conducted in laboratory mice. By measuring the BIN1 level in the heart or in the bloodstream, we believe we can approximate the health of the heart and prognosticate patient outcome because we know BIN1 is decreased in heart failure. This gives us a target: If we can restore or replace the BIN1, perhaps we can rescue failing hearts.

The surface of muscle cells in the main pumping chamber of the heart the left ventricle is dimpled like a golf ball, but the dimples form deep pockets called T-tubules. Molecules of electrically charged chemicals linger inside the tubules, waiting to rush through gated channels of the cell membrane into the cell. When calcium enters the cell, the heart cell contracts. An outflow of potassium molecules counteracts the calcium influx and allows the cell to relax.

Shaws group, which has studied BIN1 for seven years, previously found that BIN1 allowed calcium channels to localize to the T-tubules, establishing pathways for calcium to get into the cell. They also found that BIN1 could be detected in the bloodstream as well as in the heart, that heart BIN1 is decreased by 50 percent in advanced stages of the most common forms of heart failure, and that low levels of BIN1 in the blood are a predictor of heart rhythm disturbances.

Heart researchers used to speculate that the BIN1 protein was responsible for making the T-tubules themselves, but Shaws group found that the pockets exist even in the absence of the protein.

In this study, using specialized microscopes, we could see that even though the T-tubules were still there, they looked very different. We discovered that although BIN1 does not create the tubule, it shapes it. The tubule was thought to be a very smooth dip of the membrane, but we now know there is a very complex folding, where BIN1 sculpts microfolds within the tubule, Shaw said.

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Cedars-Sinai Study Identifies Heart-Specific Protein That Protects Against Arrhythmia