excitation-contraction coupling in the heart, then and now. (A) Classic, common-pool theory of EC coupling. (B) current, local mechanism EC coupling control. (C) Defects in the EC coupling during cardiac dysfunction.
The researchers found that a diet high in salt causes subtle biochemical changes that can fatally shaking heart rate in rats with high blood pressure. The results, reported in tomorrow's issue of Science * suggest how untreated hypertension in people can lead to chronic heart failure.
Doctors have long thought that in a hypertensive person, the heart adapts to stress by expanding to pump blood more efficiently. Thinking such swelling may not be as benign, W. Jonathan Lederer and colleagues at the University of Maryland School of Medicine in Baltimore probed the mechanism by which the heart muscle cells to absorb calcium, which causes the heart to contract. They fed a high salt diet in a strain of rats bred to have high blood pressure, and analyzed changes in calcium channel moves into a cell to trigger contraction.
The researchers found that the differences between the calcium channels and calcium receptors located just inside the cell membrane had expanded. Initially, however, the rats have overcome this defect by producing additional adrenaline that the increased sensitivity of calcium receptors. But after several weeks of steady expansion, damaged hearts started to contract evil, resulting in heart failure.
Experts are impressed by the study. "What is surprising is that most of the problems seem to be a step between the electrical excitation of the heart and its contraction," says David Yue, a biomedical engineer at the School of the Johns Hopkins University of Medicine in Baltimore . Such a fundamental fatal process is also likely to occur in people, said Lederer. The message for people with high blood pressure, he said, is "Do not wait to treat, because you develop an irreversible failure." In the meantime, Lederer says, pharmaceutical companies should aim to test agents which increase the calcium receptor sensitivity in hypertensive people.
* for details, Science online subscribers can link to the full text of the report.
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