Active uptake of amino acids by the urinary bladder epithelium of rat, rabbit, and dog.

Through a series of experiments employing tissue fragments incubated in vitro together with labeled substrates, it was observed that the tight urinary bladder epithelia of rat, rabbit, and dog possess the capacity of an active accumulation of amino acids against a concentration gradient. This uptake is saturable in the presence of sodium, is sodium-dependent, and is inhibited by ouabain. In comparison with other tissues, this phenomenon of active uptake is strikingly resistant to anoxia. The direction of uptake is from blood to lumen across the basolateral epithelial membrane. The induction of hyperplasia in the bladder epithelium of dogs very significantly increased the uptake of amino acids. Further studies should confirm the presence of this phenomenon in the human bladder.