| Figure 1: Model of normal
transport function in the renal proximal tubule. Utilizing the concentration
gradient established by Na/K ATPase, Na-coupled transporters on the luminal
surface of the tubular epithelial cells remove glucose from the urine,
and excrete hydrogen ions into the urine. The hydrogen ions combine with
bicarbonate ions in the urine to form carbonic acid, which dissociates
into water and carbon dioxide (facilitated by carbonic anhydrase). The
carbon dioxide enters the epithelial cells by diffusion. |
