Potassium transport in the maturing kidney

The distal nephron and colon are the primary sites of regulation of potassium (K⁺) homeostasis, responsible for maintaining a zero balance in adults and net positive balance in growing infants and children. Distal nephron segments can either secrete or reabsorb K⁺ depending on the metabolic needs of the organism. In the healthy adult kidney, K⁺ secretion predominates over K⁺ absorption. Baseline K⁺ secretion occurs via the apical low-conductance secretory K⁺ (SK) channel, whereas the maxi-K channel mediates flow-stimulated net urinary K⁺ secretion. The K⁺ retention characteristic of the neonatal kidney appears to be due not only to the absence of apical secretory K⁺ channels in the distal nephron but also to a predominance of apical H-K-adenosine triphosphatase (ATPase), which presumably mediates K⁺ absorption. Both luminal and peritubular factors regulate the balance between K⁺ secretion and absorption. Perturbation in any of these factors can lead to K⁺ imbalance. In turn, these factors may serve as effective targets for the treatment of both hyper-and hypokalemia. The purpose of this review is to present an overview of recent advances in our understanding of mechanisms of K⁺ transport in the maturing kidney.