Molecular ultrastructure of the urothelial surface: Insights from a combination of various microscopic techniques

Abstract

The urothelium forms the blood–urine barrier, which depends on the complex organization of transmembrane proteins, uroplakins, in the apical plasma membrane of umbrella cells. Uroplakins compose 16 nm intramembrane particles, which are assembled into urothelial plaques. Here we present an integrated survey on the molecular ultrastructure of urothelial plaques in normal umbrella cells with advanced microscopic techniques. We analyzed the ultrastructure and performed measurements of urothelial plaques in the normal mouse urothelium. We used field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) on immunolabeled ultrathin sections (immuno‐TEM), and freeze‐fracture replicas (FRIL). We performed immunolabeling of uroplakins for scanning electron microscopy (immuno‐FESEM). All microscopic techniques revealed a variability of urothelial plaque diameters ranging from 332 to 1179 nm. All immunolabeling techniques confirmed the presence of uroplakins in urothelial plaques. FRIL showed the association of uroplakins with 16 nm intramembrane particles and their organization into plaques. Using different microscopic techniques and applied qualitative and quantitative evaluation, new insights into the urothelial apical surface molecular ultrastructure have emerged and may hopefully provide a timely impulse for many ongoing studies. The combination of various microscopic techniques used in this study shows how these techniques complement one another. The described advantages and disadvantages of each technique should be considered for future studies of molecular and structural membrane specializations in other cells and tissues. Microsc. Res. Tech. 77:896–901, 2014. © 2014 Wiley Periodicals, Inc.

Urinary ATP Levels Are Controlled by Nucleotidases Released from the Urothelium in a Regulated Manner

“…Next, we asked whether the release of s-NTDs in the bladder lumen during filling is a regulated process. Bladder urothelium umbrella cells contain a large pool of subapical discoidal or fusiform vesicles (DFVs) [ 80 , 81 ] that undergo regulated exocytosis in response to stretch [ 82 , 83 ]. Thus, the apical cell membranes of the umbrella cells adapt to increasing tension by increasing surface with DFVs exocytosis.…”

Human Amniotic Membrane Enriched with Urinary Bladder Fibroblasts Promote the Re-Epithelization of Urothelial Injury

“…In this aspect, we would also like to point out the importance of the ultrastructural analysis in the process of determination of the urothelial differentiation stage. Moreover, based on the ultrastructural characterization of the superficial urothelial cells, we can also assume the functionality of the established urothelial 14 , 35 – 37 .…”

Properties of the Urothelium that Establish the Blood–Urine Barrier and Their Implications for Drug Delivery

“…The hinges in (d) correspond to the microridges seen in (f) and (f´) (red arrowheads in enlarged inset). Inside the microridges lies the urothelial plaque, as we demonstrated in Zupančič et al (2014b). Large inset framed with white lines is twice enlarged image of the corresponding small white-framed inset.…”