Cardiac Myocytes Metabolism

Cardiac myocytes metabolism plays a key role in the efficient contraction and relaxation of the heart muscle fiber. Every cell in the body uses fuel to produce energy so that it can function properly and divide. Unlike the rest of the body cells, the cardiac myocytes can employ four different types of fuel, with which their mitochondria generate adenosine triphosphate (ATP). These fuels are sugar (glucose), ketone bodies, fatty acid, and lactate, which are metabolically processed by the cells mitochondria to obtain the energy needed for the myocardium cells contraction. Red blood cells and liver hepatocytes can only use glucose, while nerve cells employs glucose and ketone bodies as fuel. Thus, the heart muscle cells are the most metabolically flexible of them all.

When the individual eats high amounts of carbohydrate in their meal, the heart muscle cells can adapt to burn the simplest form of carbs as fuel, which is glucose (sugar), to produce ATP through a process known as glycolysis to obtain pyruvate, which is further metabolized in the Creb's cycle of the mitochondria to produce ATP. However, when man is not eating carbohydrates (bread, potatoes, sugar, etc) but only meat, entrails, butter, and cheese, or when he is fasting, his heart myocytes can quickly and easily adapt to consume either fatty acids or ketone bodies, such as β-hydroxybuterate and acetoacetate, as sources of fuel to burn for the generation of energy. Ketone bodies is produced by the liver cells mitochondria from fatty acid, which derives from the saturated fat contained in the butter, meat, entrails, etc, man eats.

The fourth type of fuel the heart muscle cells employ is lactate, which a salt of lactic acid. Lactate can replace glucose as it becomes an alternative fuel during physical exercises, when concentrations of lactate in the bloodstream increase. Lactate is the byproduct of the skeletal muscle cells glycolysis. Although skeletal muscle fibers cannot use lactate as fuel (because is causes cramp), the myocardium cells can utilize it as fuel as long as they have enough oxygen available. This is so, because myocyte mitochondria can produce enough ATP for the myocardium contraction only in aerobic conditions (with plenty of oxygen).

Myocyte oxygen consumption increases sharply when the frequency of contraction (heart rate) and force of contraction are increased. Under these physiological circumstances, more oxygen must be delivered to the heart by the coronary arteries circulation to supply the myocytes metabolic demands. Biochemical messengers dilate the coronary blood vessels to allow additional blood flow and, with it, oxygen in greater amount.