Path of osmotic water flow through rabbit gall bladder epithelium

Abstract

Osmotic, Pf, and diffusive, Pd, water permeability of rabbit gall bladder epithelial membranes have been determined. The thickness of unstirred layers, or diffusion barriers, such as cell cytoplasm and the thick supporting layer of connective tissue, have been determined by butanol diffusion, assuming unstirred layers limited diffusion of this solute.The contribution of these layers to the total resistance to 3HHO diffusion was 85.7 ± 2.9% (S.E.). The measured ratio of the water permeabilities, Pf/Pd, decreased from 26.3 ± 4.3 to 3.1 ± 0.3 after making corrections of Pd for unstirred layer influences.The temperature dependence of Pf has also been determined. Arrhenius plots of Pf show breaks at 10–15 and 20 °C at osmotic gradients of 100 and 200 mM sucrose, respectively. Below these temperatures, apparent activation energies amounted to 9.7 ± 1.5 kcal/sdmole−1, values which are consistent with a solubility-diffusion mechanism in the water permeation process. Above the break temperature, apparent activation energies decreased to 3.5 ± 0.6 kcal·mole−1 which is consistent with values for water permeation through aqueous pores.These results suggest that osmotic flow through gall bladder mucosa is mainly via the cellular membranes, i.e. the extracellular shunt, which is the main route for passive ion permeation, does not contribute significantly to the osmotic water flow in response to a sucrose gradient.