Single proximal tubules of Necturus kidney. VIII: Na and K determinations by glass electrodes

¹ Biophysical Laboratory, Harvard Medical School, Boston, Massachusetts

Cation-sensitive glass electrodes have been used to measure Na and K concentrations in Necturus serum and in glomerular and proximal tubular fluid from Necturus kidney. It has been found that the ratio [Na]_glomerulus/[Na]_serum is 1.00 ± 0.02 and the ratio [Na]_tubule/[Na]_glomerulus is 0.99 ± 0.01 thus confirming previous measurements with the flame photometer which indicated that tubular Na concentration did not change as fluid moved along the proximal tubule in Necturus kidney. These results were also confirmed with cation electrodes placed in situ in the living animal. The K concentration in fluid collected from the most distal portion of the proximal tubule was found to be 1.8 ± 0.1 times more concentrated than that in the glomerulus, in agreement with a ratio of 1.6 ± 0.1 previously obtained on the basis of flame photometer measurements by Oken and Solomon.