Acid base problems

While the main H⁺ pump in the PCT is NHE-3, the main H⁺ pump in the DCT is an H⁺ATPase:

The H⁺ ATPases have a low capacity but generate a steep [H⁺] gradient.

Luminal H⁺ acceptors (NH₃) are required for H⁺ pumping to continue.

A H⁺ ATPase is located in the luminal membrane. It helps to reabsorb any remaining filtered HCO₃^- and also permits an increased renal excretion of NH₄⁺. However, in the absence of a luminal H⁺ acceptor (NH₃) the free [H⁺] in the tubular fluid rises quickly (max 0.1 mmol/l), stopping further H⁺ secretion – minimum urine pH is 4.

There is also an H⁺/K⁺ ATPase, which has a low capacity and seems to be important primarily for the reabsorption of K⁺ in states of K⁺ depletion and hypokalaemia.

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