Expression, localization, and functional properties of inwardly rectifying K⁺ channels in the kidney

Inwardly rectifying K⁺ (K_ir) channels are expressed in multiple organs and cell types and play critical roles in cellular function. Most notably, K_ir channels are major determinants of the resting membrane potential and K⁺ homeostasis. The renal outer medullary K⁺ channel (K_ir1.1) was the first renal K_ir channel identified and cloned in the kidney over two decades ago. Since then, several additional members, including classical and ATP-regulated K_ir family classes, have been identified to be expressed in the kidney and to contribute to renal ion transport. Although the ATP-regulated K_ir channel class remains the most well known due to severe pathological phenotypes associated with their mutations, progress is being made in defining the properties, localization, and physiological functions of other renal K_ir channels, including those localized to the basolateral epithelium. This review is primarily focused on the current knowledge of the expression and localization of renal K_ir channels but will also briefly describe their proposed functions in the kidney.