type 2 tubular acidosis and hypokalemia

[LuckiestOne]

Why does Type 2 tubular acidosis (where bicarb is not absorbed from PCT) also cause hypokalemia? Thanks in advance.

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[Boardz]

Why does Type 2 tubular acidosis (where bicarb is not absorbed from PCT) also cause hypokalemia? Thanks in advance.

Type 1 RTA occurs because the alpha-intercalated cell has defunct H+/K+ exchange pumps- therefore, since you cannot pump H+ into the lumen, you become acidotic, and because you can't take K+ out in this region either, you become Hypokalemic.

Type 2 RTA occurs because for a variety of reasons (defunct Na+/Bicarb cotransporter, Carbonic Anhydrase deficiency, etc.), you cannot reabsorb bicarbonate in the proximal tubule. This increases Na+ delivery to the collecting duct, where Na+ is reabsorbed at the expense of K+ excretion. This occurs to maintain charge neutrality.

Uptodate has an excellent article on this: "Pathophysiology of renal tubular acidosis and the effect on potassium balance"

 

[LuckiestOne]

Type 1 RTA occurs because the alpha-intercalated cell has defunct H+/K+ exchange pumps- therefore, since you cannot pump H+ into the lumen, you become acidotic, and because you can't take K+ out in this region either, you become Hypokalemic.

Type 2 RTA occurs because for a variety of reasons (defunct Na+/Bicarb cotransporter, Carbonic Anhydrase deficiency, etc.), you cannot reabsorb bicarbonate in the proximal tubule. This increases Na+ delivery to the collecting duct, where Na+ is reabsorbed at the expense of K+ excretion. This occurs to maintain charge neutrality.

Uptodate has an excellent article on this: "Pathophysiology of renal tubular acidosis and the effect on potassium balance"

Ty for your response. Can you elaborate on the connection between bicarb cotransporter and Na delivery increase? That's the part that I am unclear on. Thank you.

 

[Boardz]

Ty for your response. Can you elaborate on the connection between bicarb cotransporter and Na delivery increase? That's the part that I am unclear on. Thank you.

There are Na+/Bicarbonate cotransporters in the basolateral membrane of the proximal tubule.

edit: for elaboration. - So, you aren't absorbing bicarb in the proximal tubule which means you can't use the Na+/Bicarb cotransporter, which means you increase Na+ delivery to the collecting duct.

Here, you reabsorb the Na+ but at the expense of excreting K+ through the principal cell to maintain charge neutrality. Thus, you end up with hypokalemia.