**2.2 Potassium movement in the thin loop of Henle**

Potassium may be secreted in the thin descending loops of Henle that penetrate the inner medulla, whilst the thin ascending loop is permeable to sodium and potassium and allows some uptake.

The thin ascending limbs of the loops of Henle (among other nephron segments) express the CLC-KA chloride channel, with its subunit Barttin. Polymorphisms in *CLCNKA* have recently been associated with a hyperreninemic hyperaldosteronism, implicating a key role for this channel in regulating renal salt handling and determining a set point for renin and angiotensin levels (Cappola, et al., 2011).
