Analysis of membrane structure in the transitional epithelium of rat urinary bladder: 1. The luminal membrane

Abstract

The structure of the luminal membrane of rat urothelium as observed with the frozen-surface and freeze-fracture replica techniques is described. Plaques, which are composed of hexagonally arranged subunits, constitute 73% of the membrane area. Data on the size and organisation of the subunits and other membrane components are presented. The structure of the subunits as seen in optically filtered and unprocessed images of the E-surface and the E- and P-fracture faces of the membrane is discussed with reference to current concepts of the events associated with the fracturing and replication of frozen membranes. Differences between the E-face and E-surface subunit structure are explicable in terms of deformation induced by fracturing and other technical considerations. The effect of glutaraldehyde fixation on the fracturing behavior of subunits and the occurrence of subunits in a dispersed arrangement are also discussed. The interplaque areas of the luminal membrane exhibit small, inconspicuous intramembrane particles on the P-face and E-face, and a rugose appearance at the E-surface. These structures may correspond to protein components other than those of the subunits which have been characterized in biochemical studies.