columnar/cuboidal epithelial cell kidney epithelial cell renal principal cell ZFA:0005322 Renal principal cells are the major cell type in the initial collecting tubule and the cortical and outer medullary collecting ducts, as well as the connecting tubule, in the nephrons of the kidneys. A key function of renal principal cells is the regulation of water balance in the body. These cells express aquaporin-2 (AQP2) water channels, which facilitate the reabsorption of water from the fluid within the renal tubule lumen back into the blood. The translocation of AQP2 to the cell membrane is controlled by the hormone vasopressin: In response to high vasopressin levels, AQP2 moves to the cell membrane, allowing water to pass through effectively and be reabsorbed, therefore concentrating the urine. Conversely, in low vasopressin conditions, AQP2 is removed from the membrane, reducing water reabsorption and diluting the urine. Renal principal cells are also involved in the regulation of sodium and potassium levels in the body. They have sodium channels (ENaC) in their luminal membranes which permit the reabsorption of sodium ions from the tubule fluid back into the blood, resulting in a net reabsorption of sodium ions into the systemic circulation. This process is controlled, in part, by the hormone aldosterone. Additionally, renal principal cells contain potassium channels that facilitate the secretion of potassium ions into the urine. The activities of these channels, in coordination with other cell types in the nephron, are critical for maintaining electrolyte balance and overall body homeostasis. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) A cuboidal epithelial cell of the kidney which regulates sodium and potassium balance. The activity of sodium and potassium channels on the apical membrane of the cell is regulated by aldosterone and vasopressin. In mammals this cell type is located in the renal collecting duct system.