Final answer:
Glucose concentration in kidney tubular cells is maintained at high levels by sodium-glucose symporters that utilize the sodium ion gradient established by Na+/K+ ATPases for secondary active transport.
Step-by-step explanation:
The concentration of glucose in tubular epithelial cells, such as those in the kidneys, is maintained by a type of transporter called a sodium-linked secondary active transporter. In particular, a sodium-glucose symporter (SGLT) on the apical membrane of these cells utilizes the sodium ion gradient established by the Na+/K+ ATPase on the basal membrane.
The symporter harnesses this gradient to co-transport sodium ions and glucose into the cell, moving glucose against its concentration gradient, into the epithelial cells from the tubular lumen. Subsequently, glucose then exits the cell into the interstitial space via facilitated diffusion.