title: Relationship of aggregated intramembranous particles to water permeability in vasopressin-treated toad urinary bladder.
abstract: It has been previously demonstrated with freeze-fracture electron microscopy that vasopressin induces specific structural alterations of the luminal membrane of granular cells from toad urinary bladder in a dose-dependent fashion. These alterations consist of aggregated intramembranous particles and are observed both in the presence and absence of an osmotic gradient. We examined the effect of methohexital, a selective inhibitor of vasopressin-stimulated water flow, and the effect of phloretin, a selective inhibitor of urea permeability, on the structure of the granular cell luminal membrane. Methohexital treatment of the vasopressin-stimulated toad bladder reduced both the osmotic water flow and vasopressin-induced alterations of membrane structure to the same extent. Phloretin reduced urea permeability but not water flow or particle aggregation. Since neither agent affects vasopressin-stimulated sodium movement, these findings indicate that the phenomenon of particle aggregation is specifically related to vasopressin-induced water permeability and not to changes in urea or sodium permeability.
mesh_terms: D000818:Animals; D001001:Anura; D002024:Bufo marinus; D002462:Cell Membrane / Q000648:ultrastructure*; D066298:In Vitro Techniques; D008723:Methohexital / Q000494:pharmacology; D010539:Permeability; D010693:Phloretin / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D014667:Vasopressins; D008723:Methohexital; D010693:Phloretin