Directing two-way traffic in the kidney: A tale of two ions

The kidneys regulate levels of Na(+) and K(+) in the body by varying urinary excretion of the electrolytes. Since transport of each of the two ions can affect the other, controlling both at the same time is a complex task. The kidneys meet this challenge in two ways. Some tubular segments change the coupling between Na(+) and K(+) transport. In addition, transport of Na(+) can shift between segments where it is coupled to K(+) reabsorption and segments where it is coupled to K(+) secretion. This permits the kidney to maintain electrolyte balance with large variations in dietary intake.