Glucose transporters in healthy heart and in cardiac disease

Heart consumes more energy than any other organ. It can utilize various metabolic substrates as a source of energy. The primary substrates are free fatty acids, especially long-chain fatty acids and glucose. The lipid bilayer of plasmalemma is impermeable for glucose. Therefore, glucose transport across the plasma membrane is mediated via glucose transporters. In human, cardiac cells are expressed as 2 families of glucose transporters: GLUTs and SGLTs. These transport proteins are GLUT1, GLUT3, GLUT8, GLUT10, GLUT11, GLUT12 and SGLT1. In human heart, GLUT4 is the major isoform that represents approximately 70% of the total glucose transporters. The changes observed in diabetic heart showed that type 1 diabetes mellitus alters the expression and translocation of GLUT4 and GLUT8 in the atria. In diabetic atria, the content in cell surface of these glucose transporters is downregulated. Expression of SGLT1, is increased in patients with end-stage cardiomyopathy secondary to type 2 diabetes. Increased expression of SGLT1 is a compensatory mechanism to the reduction in cardiac GLUT1 and GLUT4 expression. In animal model of type 1 diabetes, the expression of Sglt1 transporter is significantly decreased, and in the animal model of type 2 diabetes it is significantly increased. In heart diseases, such as cardiac hypertrophy (that is similar to fetal heart), heart failure and myocardial ischemia different perturbations in expression of glucose transporters are observed, especially in GLUT1 and GLUT4, due to changes in heart glucose metabolism. In this article, the functions of glucose transporters in healthy heart and in cardiac diseases are reviewed.