Transport of fatty acids in the heart.
Fatty acids are taken up by the myocardium in the unesterified form, either directly from the unbound pool of free fatty acids in the plasma or following release from plasma triglycerides by lipoprotein lipase. They pass extremely rapidly into the cardiac cells, where their distribution is determined by a number of physical and biochemical factors. For the intracellular spaces these factors are essentially physical and depend on gradients of concentration of unbound fatty acids and on the concentration and affinity of protein binding sites. In the cytoplasm of the myocardial cell, myoglobin seems to play a specific carrier role. Passage of fatty acids across cell membranes depends on their chemical forms and, largely, on the degree of solubility of these forms in the lipid layer of the membranes. In addition, there may be specific transport systems, such as is mediated by carnitine in the inner mitochondrial membrane. Finally, the mass movement on fatty acids through the cells depends on the rate at which they are removed by oxidation or esterification. Under normal conditions, these various factors lead to a rapid movement of fatty acids into the mitochondria where they are oxidised and a more gradual esterification into complex lipids.