The cardiac muscle cell.

The cardiac myocyte is the most physically energetic cell in the body, contracting constantly, without tiring, 3 billion times or more in an average human lifespan. By coordinating its beating activity with that of its 3 billion neighbours in the main pump of the human heart, over 7,000 litres of blood are pumped per day, without conscious effort, along 100,000 miles of blood vessels. A detailed picture of the membrane organisation of the cardiac muscle cell underpins our understanding of how the electrical impulse, generated within the heart, stimulates coordinated contraction of the cardiac chambers. This article highlights, with the aid of modern cellular imaging methods, key components of the membrane machinery responsible for coupling electrical excitation and contraction in the cardiomyocyte, focusing on plasma membrane/sarcoplasmic reticulum and plasma membrane/plasma membrane junctions. BioEssays 22:188-199, 2000.