Glutaraldehyde fixation preserves the permeability properties of the ADH-induced water channels

Unidirectional and net water movements were determined, in frog urinary bladders, before and after glutaraldehyde fixation. Experiments were performed in three experimental conditions: in nonstimulated preparations, after the action of antidiuretic hormone (ADH) and in nonstimulated preparations to which amphotericin B was incorporated from the luminal bath. As previously observed for net water fluxes, the increase in the unidirectional water movement induced by ADH was well preserved by glutaraldehyde fixation. After correction for the effects of unstirred layers and nonosmotic pathways, the observed correlation between the ADH-induced increases in the osmotic (Pf) and diffusional (Pd) permeability coefficients was not modified by the fixative action (before glutaraldehyde: slope 11.19, r: 0.87 +/- 0.07; n = 12; after glutaraldehyde: slope 10.67, r: 0.86 +/- 0.04, n = 39). In the case of amphotericin B, delta Pf/delta Pd = 3.08 (r: 0.83 +/- 0.08), a value similar to that observed in lipid bilayers or in nonfixed toad urinary bladders. It is concluded that: The experimental approach previously employed to study water channels in artificial lipid membranes and in amphibian urinary bladders, can be applied to the glutaraldehyde-fixed frog urinary bladder. Glutaraldehyde fixation does not modify the permeability properties of the ADH-induced water channels. Any contribution of exo-endocytic processes or cell regulatory mechanisms to the observed permeability parameters can probably be excluded. Glutaraldehyde-fixed preparations are a good model to characterize these water pathways.