Osmotic and solute permeabilities of isolated urinary bladder of the trout
Fossat, B.; Lahlou, B.
American Journal of Physiology 233(6): F525-F531
1977
ISSN/ISBN: 0002-9513 PMID: 596451 Document Number: 116693
Urinary bladders dissected from trout [Salmo irideus] were studied in vitro by the sac technique. Transepithelial osmotic gradients were created by stepwise modification of the mucosal solution, the serosal medium having been kept constant as Ringer solution (300 mOsmol/l. In the absence of osmotic gradient, water transport was linked to active absorption of NaCl and was not induced by mannitol or raffinose. When Na was absent in the lumen the osmotic flow (mucosa to serosa) was linear with the osmotic gradient, and the true osmotic permeability was 8 .times. 10-6 .mu.l .cntdot. cm-2 .cntdot. s-1 mOsmol-1. No rectification of solvent flow was observed with mannitol; this rectification was 60% with raffinose. The Staverman reflection coefficient for NaCl was high with respect to these solutes: 1 and 0.95, respectively. Urea induced a complex variation of osmotic flow assumed due to a reflection coefficient decreasing steadily with increasing concentrations of this solute in the mucosal medium. Solute passive permeability (in cm/s) measured with radiolabeled substrates varied within a relatively narrow range (1-17) for a large scale of MW: urea, 6.2 .times. 10-6 at 100 mM and 30 .times. 10-6 at 800 mM; Na and mannitol, 3.8 .times. 10-6; inulin, 7 .times. 10-7; dextran 75,000, 3.6 .times. 10-7. These specific properties were in agreement with the osmoregulatory role assumed for this tissue.