Analysis of the three-dimensional structure of the urinary bladder epithelial cell membranes.

The three-dimensional structure of the luminal membrane of the mammalian urinary bladder has been determined using electron micrographs of tilted membranes preserved in neutralized potassium phosphotungstate stain. The density map consists of 12 stain-excluding regions, 57 A thick, that are organized as an inner ring of 6 and an outer ring of 6, plus a small stain-excluding feature directly on the sixfold axis. Only the luminal surface of the membrane can be observed suggesting that at the resolution of the reconstruction the cytoplasmic surface is smooth.