Abstract
AbstractThe diffusional water permeability in rat proximal tubules was studied in microperfusion experiments with triturated water. The perfusion solutions were chosen either to give no net flux or a net water flux in either direction. The diffusional water permeability at zero net water flux was 564. 10‐‐5 cm/sec. The significance of the permeability measurements made during a net flux is discussed. The osmotic water permeability was 15. 10‐‐8 cm3 cm‐2 sec‐1. (cm H2O)‐l The large differences between osmotic water permeability and diffusional water permeability in zero net flux conditions cannot be accounted for entirely by an unstirred layer effect and are interpreted to mean that water transport along osmotic gradients is mainly a bulk flow through aqueous pores and not a diffusional flow and that the proximal tubular wall is a highly porous membrane.
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