Micropuncture study of renal potassium excretion in the rat

TLDR

The study collected proximal and distal tubular fluid from rats on control, low‑K, or high‑K, low‑Na diets, administered inulin‑C^14, and measured Na and K concentrations by dual‑channel microflame photometry and radioactivity, while transtubular electrical potentials were recorded with glass microelectrodes. Proximal tubular K TF/P ratios were slightly below unity in all groups, whereas distal tubules exhibited net K secretion into the lumen in control and high‑K, low‑Na animals, continued reabsorption in low‑K animals, and K entry driven by an electrochemical gradient.

Abstract

Samples of proximal and distal tubular fluid were collected from rats maintained 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. Transtubular electrical potential differences were measured by means of glass microelectrodes. Mean TF/P ratios for potassium in the proximal tubule were slightly below unity in all groups of animals. A comparison of the relative increase in K and inulin-C 14 along the distal tubule indicates: 1) net movement of potassium into the tubular lumen in most control animals; 2) net movement of K into the tubular lumen of high-K, low-Na, sulfate-loaded animals, and in dichlorphenamide-treated animals on a control diet; and 3) the possibility of continued net reabsorption of potassium along the distal tubule and, particularly, the collecting duct in animals kept on a low-K diet. Distal tubular entry of potassium occurs down an electrochemical potential gradient.