Distinct cell types along thick ascending limb express pathways for monovalent and divalent cation transport

Kidney thick ascending limb (TAL) cells reabsorb sodium, potassium, calcium, and magnesium and contribute to urinary concentration. These cells are typically viewed as a single type that recycles potassium across the apical membrane and generates a lumen-positive transepithelial voltage driving calcium and magnesium reabsorption, though variability in potassium channel expression has been reported. Additionally, recent transcriptomic analyses suggest that different cell types exist along this segment, but classifications have varied and have not led to a new consensus model. We used immunolocalization, electrophysiology, and enriched single-nucleus RNA-Seq to identify TAL cell types in rats, mice, and humans. We identified 3 major TAL cell types defined by expression of potassium channels and claudins. One has apical potassium channels, has low basolateral potassium conductance, and is bordered by a monovalent cation-permeable claudin. A second lacks apical potassium channels, has high basolateral potassium conductance, and is bordered by calcium- and magnesium-permeable claudins. A third type also lacks apical potassium channels and has high basolateral potassium conductance, but these cells are ringed by monovalent cation-permeable claudins. The recognition of diverse cell types may resolve longstanding questions about how solute transport can be modulated selectively and how disruption of these cells leads to human disease.