The Isolated Duct of the Rat Cauda Epididymidis as a Model for Isosmotic Transport Studies

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Abstract
Electrolytes and water transport have been studied in the perfused isolated duct of the rat cauda epididymis in vitro. The rates of reabsorption of Na+, Cl- and water and of secretion of K were comparable to those in the perfused rat cauda epididymidis in vivo. Na+ reabsorption was isotonic and inhibited by the metabolic uncoupler 2,4-dinitrophenol and cooling. Removal of Na+ ions from the intraluminal fluid abolished water reabsorption in the isolated duct. When K+ ions were removed from the peritubular medium the secretion of K was abolished, but the reabsorption of Na+ and water was unaffected. Under this condition, the reabsorption of Cl- was enhanced. Removal of Ca ions from the lumen increased the rates of Na and water reabsorption and K secretion by 2-fold. Amiloride (10-4 M) added to the intraluminal fluid had no effect on the electrolyte and water transport in the isolated duct, whereas triaminopyrimidine produced a dose-dependent inhibition of Na and water reabsorption when added to both sides. Na and water reabsorption were inhibited by the application of ouabain (10-3 M) to the peritubular side and of ethacrynic acid (10-4 to 10-3 M) to the luminal side. These results are discussed in the light of the recent concepts of isosmotic transepithelial transport.