Endothelial cells form the inner layer of the vascular system. They ensure the transport between blood and insterstitium and take part in the regulation of vascular tonus, in the equlibrium of thrombosis/thrombolysis, and in immune processes.
Therefore an endothelial cell has very high energetic demands. The most important source of energy for the endothelium, even in aerobic conditions, is the anaerobic glycolysis.
That is why endothelial cells are not very sensitive to hypoxia. Intracellular transport of glucose is independent on insulin.
Fatty acids, lactate, glutamine, and phosphocreatine can perform as other energetic substrates. Their utilisation rises especially with the insufficiency of glucose.
Moreover this condition combined with hypoxia causes the energetic breakdown of the cell.