Renal transport sites for K, H and NH₃. Effect of impermeant anions on their transport

¹ Department of Physiology, School of Medicine, University of Michigan, Ann Arbor, Michigan

The stop flow technique was used to locate the sites of the renal transport mechanisms for potassium, hydrogen and ammonium. Data were obtained which indicate that these cations are secreted in a very distal area of the nephron, presumably in the collecting ducts. Potassium reabsorption also occurs in a distal area immediately proximal to the secretory site. Infusions of thiosulfate, ferrocyanide and phosphate alter the stop flow concentration patterns so that secretion of the cations appears to take place throughout the distal tubule and to be coextensive with distal sodium reabsorption. No clear indication of potassium reabsorption is evident under these circumstances. It is suggested that these anions, because of the impermeability of the distal tubule to them and because of their negative charge, attract hydrogen and potassium into the tubular lumen as sodium is reabsorbed. In effect, an abnormal exchange mechanism is created at a site proximal to that where active secretion of hydrogen and potassium occurs.