Polycations reduce vasopressin-induced water flow by endocytic removal of water channels

Several polycations added to the luminal solution were found to inhibit the vasopressin (ADH)-induced water flow in toad urinary bladder but not the ADH-induced increase in sodium transport or in urea permeability. Ultrastructural studies were conducted to evaluate the uptake of cationized ferritin. It was found that endocytosis of cationized ferritin by luminal cells was strikingly enhanced on exposure to ADH; this increased endocytosis was concomitant with inhibition of transepithelial ADH-induced water flow. Various maneuvers preventing endocytosis were also found to counteract the polycation-induced inhibition of the ADH effect. It is suggested that polycations are endocytosed in vesicles whose walls contain the water channels but not the urea or sodium channels.