MEMBRANE-ASSOCIATED PARTICLES - DISTRIBUTION IN FROG URINARY-BLADDER EPITHELIUM AT REST AND AFTER OXYTOCIN TREATMENT

The fine structure of the plasmic membrane of the frog urinary bladder epithelium was studied with a freeze-etching EM technique. The external face of the cytoplasmic leaflet (A face) of the apical membrane of epithelial cells is characterized by a markedly reduced number of membrane associated particles compared to the value observed on the A face of the lateral membranes of these cells. The existence after oxytocin treatment of numerous spots of clustered particles is demonstrated. These characteristics are present in unfixed glycerinated cells but are more clearly observed after prefixation of glycerol treated cells with glutaraldehyde. The oxytocin induced clustering is completely reversible. These ultrastructural features are probably related to the permeability properties of the apical barrier and to their control by antidiuretic hormone.