Thick ascending limb cell

Schematic diagram of thick ascending limb cell demonstrating proteins that are affected in patients with Bartter syndrome (BS). BS is classified based on the affected protein as noted in the diagram:

• BS1 – NKCC2
• BS2 – ROMK/KCNJ1/Kir1.1
• BS3 (includes Gitelman-like syndrome) – ClC-Kb
• BS4a – Barttin
• BS4b – ClC-Ka and ClC-Kb
• BS5 – MAGE-D2

Note that the combined actions of the ROMK and the basolateral chloride channels lead to epithelial polarization, with the lumen positive with respect to blood. This drives paracellular cation reabsorption.