Abstract
It was recently reported(l) that approximately 30% of the total albumin content of the kidney is present in the interstitial space. Since urea concentration is high(2) and pH may be alkaline(3) in the renal medullary in-terstitium, it was of interest to find out how albumin affects the transport of fluid and urea into an environment of high salt and urea concentrations and of high pH.
Phosphate buffer solutions were arranged in the manner of a 2-way, 3 by 4 contingency table: pH values were adjusted to 5.0, 7.4 and 9.5, and urea concentrations were set at 0, 0.005 M, 0.3 M and 1.0 M, respectively. All solutions contained XaCl at a concentration of 0.4 M and approximately 2 μC/ liter of C14-urea. A volume of one hundred ml of each of these solutions was used as the bathing fluid during dialysis. A 30% bovine serum albumin in Tyrode's solution (National Biochemical Corp.) was diluted with the buffers to obtain 5% albumin solutions. The pH values were readjusted after addition of the albumin. Eight ml samples of the albumin solutions were placed in cellophane bags. The bags were made of cellophane tubing (Union Carbide Corp.) which was soaked in a sodium phosphate solution of pH 10 for 24 hours prior to experiment, then copiously washed with tap water and distilled water. Ample space was provided in the bags for an increase in volume and no hydrostatic pressure developed in the albumin solutions. Dialysis was carried out for 72 hours and in triplicate for each pH and urea concentration. The samples were gently and continuously shaken in stoppered containers at 25°C. The net inflow of solution was determined as the difference between initial and final weights of the bags containing the albumin.
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