Micropuncture study of renal potassium excretion in the rat (Reprinted from Am. J. Physiol., vol 206, pg 674-686, 1964)

Samples of proximal and distal tubular fluid were collected from rats maint ained on a control, a low-K, or a high-K, low-Na diet. All animals received inulin-C-14. Plasma (P) and tubular fluid (TF) were analyzed for Na and K by dual-channel microflame photometry and assayed for radioactivity. Transt ubular electrical potential differences were measured by means of glass mic roelectrodes. Mean TF/P ratios for potassium in the proximal tubule were sl ightly below unity in all groups of animals. A comparison of the relative i ncrease in K and inulin-C-14 along the distal tubule indicates: 1) net move ment of potassium into the tubular lumen in most control animals; 2) net mo vement of K into the tubular lumen of high-K, low-Na, sulfate-loaded animal s, and in dichlorphenamide-treated animals on a control diet; and 3) the po ssibility of continued net reabsorption of potassium along the distal tubul e and, particularly, the collecting duct in animals kept on a low-K diet. D istal tubular entry of potassium occurs down an electrochemical potential g radient.