Regulation of Potassium Excretion in the Kidney

ABSTRACT

The maintenance of potassium balance depends primarily on excretion by the kidney. The regulated secretion of potassium normally accounts for most of urinary potassium excretion. Potassium transport along the nephron has two main featuresthe ubiquitous Na,K-ATPase defines basolateral membranes, whereas site-specific potassium transporters are responsible for the apical transport. Two different cell types mediate secretion and reabsorption of potassium. Principal cells secrete potassium, whereas intercalated cells, especially those belonging to the subfamily of beta-intercalated cells, reabsorb potassium. The factors that stimulate potassium secretion by the principal cells include (1) increased extracellular fluid potassium concentration (2) increased aldosterone and (3) increased tubular flow rate. One factor that decreases potassium secretion is increased hydrogen concentration (acidosis). In situations associated with severe potassium depletion, there is a cessation of potassium secretion and net reabsorption of potassium. It is believed that H,K-ATPase transport mechanism located in the luminal membrane of the cortical and outer medullary collecting duct cells reabsorb potassium in exchange for hydrogen secreted into the tubular lumen.