This is an energy-requiring process that transports glucose “against” a concentration gradient—that is, from low glucose concentrations outside the cell to higher concentrations within the cell. This system is a carrier-mediated process in which the movement of glucose is coupled to the concentration gradient of Na + , which is transported into the cell at the same time. The carrier is a sodium-depen- dent–glucose transporter or SGLT. This type of transport occurs in the epithelial cells of the intestine (see p. 87), renal tubules, and choroid plexus. [Note: The choroid plexus, part of the blood brain barrier, also contains GLUT-1.]