Micropuncture study of renal excretion of water, K, Na, and Cl in Necturus

Abstract

Inulin, sodium, potassium, and chloride were determined on identical samples of serum and fluid collected from the kidney tubules of Necturus under urethan anesthesia. Inulin fluid-serum ratios obtained were as follows: highest ratios for proximal tubules approximated 2, indicating a reabsorption of about 50%, of filtered water; highest ratios for distal tubules were near 3.4; ratios for sodium remained near 1 in proximal tubules, tending to be lowest near the ends of the segments. There was an abrupt drop in sodium concentration in the early part (thin segment) of the distal tubules, which may be made possible by the better oxygen supply in this region. Chloride ratios rose to 1.12 in the proximal tubules and chloride concentrations fell over the same region, as did sodium. Potassium ratios remained close to 1 in the proximal tubules, indicating that up to one-half of the filtered potassium may be reabsorbed there. Distal tubule potassium ratios showed great variability, some being higher and some lower than 1.