Osmotic properties of isolated turtle bladder

Abstract

Variations in the composition of mucosal fluid induced reproducible changes of transport rates of water and salt across the isolated bladder wall of Pseudemys turtles. The bladders, removed from three different sets of turtles, were mounted in the form of sacs, and incubated so that the serosal surfaces were bathed by oxygenated Ringer solution in all cases. Set 1. Increasing chloride concentration of isoosmotic mucosal fluid from 0 to 110 mEq/liter resulted in increasing rates of water and salt loss. Rate of weight loss vs. mucosal chloride concentration yielded a Michaelis pattern with an apparent K_m of 13 mEq/liter. Set 2. When mucosal solutions were pure sucrose, the rate of weight loss increased in a curvilinear manner with increasing gradients of osmotic activity across bladders. The nonlinear pattern was ascribed to observed changes in dimensions of the bladder wall and consequently to changes of concentration profiles in boundary layer fluids in the bladder. Set 3. When mucosal fluids were pure NaCl, the rate of weight loss vs. mucosal osmotic activity followed the pattern predicted from simple addition of water flows in sets 1 and 2. This, together with the observed independence between salt and water movement, indicated that the two forces imposed (transbladder osmotic gradient and salt pumping) act additively to induce transbladder movement of water.