New aspects of renal potassium transport.

The kidney's major role in potassium (K) homeostasis depends on its ability to respond effectively to changes in external K balance and to stabilize the extracellular concentration of K. The correction of deviations from normal plasma K levels and the maintenance of external K balance depend on the intrinsic ability of distal nephron segments to either secrete or reabsorb K. Net K secretion occurs mainly in principal cells while K absorption takes place in intercalated cells. Studies on single tubules and principal and intercalated cells have defined the determinants of K secretion and reabsorption including the electrochemical driving forces, specific carriers, ATPases, and K channels. Recent studies on the properties and molecular identity of renal K channels have also contributed significantly to understanding the renal mechanisms that transport and regulate K excretion.