Abstract
To determine the three-dimensional structure of the lumenal membrane of transitional epithelium, a study was made of sectioned, negatively stained, and freeze-etched specimens from intact epithelium and membrane fractions from rabbit urinary bladder. Particulate membrane components are confined to plaque regions within which the unit membrane is asymmetric, having a thicker outer leaflet. Transversely fractured freeze-etched plaques display a thick (∼80 A), particulate lumenal leaflet and a thin (∼40 A) cytoplasmic one. Four different faces of the two leaflets can be distinguished: two complementary, split, inner membrane faces exposed by freeze-cleaving the bilayer and two external (lumenal and cytoplasmic) membrane surfaces revealed by deep-etching. On the split, inner face of the lumenal leaflet appear polygonal plaques of hexagonally arranged particles. These fit into holes observed on the complementary, split, innerface of the cytoplasmic leaflet. The particles, which have a center-to-center spacing of ∼160 A, also seem to protrude from the external surface of the lumenal leaflet, where their subunits (∼50 A in diameter) are revealed by freeze-etching and negative staining. The plaques are separated from each other by smooth-surfaced regions, which cleave like simple lipid bilayers. Since the array of plaque particles covers only ∼73% of the membrane surface area, whereas 27% is taken up by particle-free interplaque regions, the presence of particles cannot in itself entirely account for the permeability barrier of the lumenal membrane. Although no particles are observed protruding from the cytoplasmic surface of the membrane, cytoplasmic filaments are attached to it by short, cross-bridge-like filaments that seem to contact the particles within the membrane. These long cytoplasmic filaments cross-link adjacent plaques. Therefore, we suggest that at least one function of the particles is to serve as anchoring sites for cytoplasmic filaments, which limit the expansion of the lumenal membrane during distention of the bladder, thereby preventing it from rupturing. The particle-free interplaque regions probably function as hinge areas between the stiff plaques, allowing the membrane to fold up when the bladder is contracted.
Full Text
The Full Text of this article is available as a PDF (2.4 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Benedetti E. L., Emmelot P. Electron microscopic observations on negatively stained plasma membranes isolated from rat liver. J Cell Biol. 1965 Jul;26(1):299–305. doi: 10.1083/jcb.26.1.299. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Branton D. Fracture faces of frozen myelin. Exp Cell Res. 1967 Mar;45(3):703–707. doi: 10.1016/0014-4827(67)90175-9. [DOI] [PubMed] [Google Scholar]
- Chlapowski F. J., Bonneville M. A., Staehelin L. A. Lumenal plasma membrane of the urinary bladder. II. Isolation and structure of membrane components. J Cell Biol. 1972 Apr;53(1):92–104. doi: 10.1083/jcb.53.1.92. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Deamer D. W., Leonard R., Tardieu A., Branton D. Lamellar and hexagonal lipid phases visualized by freeze-etching. Biochim Biophys Acta. 1970;219(1):47–60. doi: 10.1016/0005-2736(70)90060-x. [DOI] [PubMed] [Google Scholar]
- ENGLUND S. E. Observations on the migration of some labelled substances between the urinary bladder and the blood in the rabbit. Acta Radiol Suppl. 1956;(135):1–80. [PubMed] [Google Scholar]
- HLAD C. J., Jr, NELSON R., HOLMES J. H. Transfer of electrolytes across the urinary bladder in the dog. Am J Physiol. 1956 Feb;184(2):406–411. doi: 10.1152/ajplegacy.1956.184.2.406. [DOI] [PubMed] [Google Scholar]
- Hicks R. M., Ketterer B. Hexagonal lattice of subunits in the thick luminal membrane of the rat urinary bladder. Nature. 1969 Dec 27;224(5226):1304–1305. doi: 10.1038/2241304a0. [DOI] [PubMed] [Google Scholar]
- Hicks R. M., Ketterer B. Isolation of the plasma membrane of the luminal surface of rat bladder epithelium, and the occurrence of a hexagonal lattice of subunits both in negatively stained whole mounts and in sectioned membranes. J Cell Biol. 1970 Jun;45(3):542–553. doi: 10.1083/jcb.45.3.542. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hicks R. M. The fine structure of the transitional epithelium of rat ureter. J Cell Biol. 1965 Jul;26(1):25–48. doi: 10.1083/jcb.26.1.25. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hicks R. M. The function of the golgi complex in transitional epithelium. Synthesis of the thick cell membrane. J Cell Biol. 1966 Sep;30(3):623–643. doi: 10.1083/jcb.30.3.623. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hicks R. M. The permeability of rat transitional epithelium. Kertinization and the barrier to water. J Cell Biol. 1966 Jan;28(1):21–31. doi: 10.1083/jcb.28.1.21. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Karnovsky M. J. The ultrastructural basis of capillary permeability studied with peroxidase as a tracer. J Cell Biol. 1967 Oct;35(1):213–236. doi: 10.1083/jcb.35.1.213. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Koss L. G. The asymmetric unit membranes of the epithelium of the urinary bladder of the rat. An electron microscopic study of a mechanism of epithelial maturation and function. Lab Invest. 1969 Aug;21(2):154–168. [PubMed] [Google Scholar]
- LUFT J. H. Improvements in epoxy resin embedding methods. J Biophys Biochem Cytol. 1961 Feb;9:409–414. doi: 10.1083/jcb.9.2.409. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Porter K. R., Kenyon K., Badenhausen S. Specializations of the unit membrane. Protoplasma. 1967;63(1):262–274. [PubMed] [Google Scholar]
- REYNOLDS E. S. The use of lead citrate at high pH as an electron-opaque stain in electron microscopy. J Cell Biol. 1963 Apr;17:208–212. doi: 10.1083/jcb.17.1.208. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Vergara J., Longley W., Robertson J. D. A hexagonal arrangement of subunits in membrane of mouse urinary bladder. J Mol Biol. 1969 Dec 28;46(3):593–596. doi: 10.1016/0022-2836(69)90200-9. [DOI] [PubMed] [Google Scholar]
- Warren R. C., Hicks R. M. Structure of the subunits in the thick luminal membrane of rat urinary bladder. Nature. 1970 Jul 18;227(5255):280–281. doi: 10.1038/227280b0. [DOI] [PubMed] [Google Scholar]