POTASSIUM-TRANSPORT - FROM CLEARANCE TO CHANNELS AND PUMPS

Potassium (K) homeostasis depends on the separate and interrelated reg ulation of K distribution between the intra- and extra-cellular fluid compartments and adequate renal excretion. This brief review focuses o n the regulation of internal K distribution and the renal mechanisms o f K handling. Based on clearance, micropuncture, and microperfusion st udies, a large body of evidence supports the view that normally, renal secretion of K determines excretion and that the principal tubule cel ls in the initial and cortical collecting tubule secrete K, whereas K reabsorption may occur in intercalated cells. Studies of the electroch emical driving forces, of intracellular ion activities, the characteri zation of several ATPases, and patch clamp investigations have provide d insight into the role of pumps and channels in those tubule cells th at regulate K secretion and reabsorption.