The distribution of Na+,K(+)-ATPase and 5A11 antigen in apical microvilli of the retinal pigment epithelium is unrelated to alpha-spectrin

J Cell Sci. 1995 Nov;108 ( Pt 11):3623-33.

Abstract

The retinal pigment epithelium was used to study the relationship between the cortical cytoskeleton and two plasma membrane proteins that associate with it. These proteins were the Na+,K(+)-ATPase, an ion pump, and the 5A11 antigen, a member of the immunoglobulin superfamily of receptor proteins. The cytoskeleton was marked by two of its constituents, alpha-spectrin and ankyrin. Ankyrin links the Na+,K(+)-ATPase to spectrin in many cells. The RPE is of interest, because unlike most epithelia it distributes the Na+,K(+)-ATPase to the apical membrane. The development of polarity was studied during chick embryogenesis. On embryonic day 6 (E6), each of these proteins was observed in the apical and lateral plasma membranes. As development proceeded, only the Na+,K(+)-ATPase was removed from the lateral membranes. Beginning on E12, ankyrin, spectrin and 5A11 appeared together in patches along the basal plasma membrane. By E16, these patches coalesced into a uniform distribution along the basal membrane. At the apical pole, alpha-spectrin appeared near the base of the microvilli, but was undetected in the microvilli themselves. This distribution resembled the distribution of alpha-spectrin in the intestine and proximal kidney tubule. By contrast, a pool of ankyrin and 5A11 and nearly all the Na+,K(+)-ATPase appeared in the microvilli. Despite its segregation from alpha-spectrin, the Na+,K(+)-ATPase appeared to associate with a macromolecular complex, as judged by extraction with Triton X-100. Changes in spectrin distribution could not be related to changes in isoform expression, as only one isoform of beta-spectrin was detected by co-immunoprecipitation with alpha-spectrin. By contrast, multiple ankyrin-like peptides could be identified by immunoblotting. These data illustrate some of the unique properties of RPE microvilli. These properties prevent the Na+,K(+)-ATPase from complexing with the alpha-spectrin-based cytoskeleton by sequestering the enzyme into the compartment where its activity is required.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Ankyrins / analysis
  • Antigens, Surface / analysis*
  • Cell Differentiation / physiology
  • Cell Membrane / chemistry
  • Cell Membrane / enzymology
  • Cell Polarity / physiology
  • Chick Embryo
  • Cytoskeleton / physiology
  • Fluorescent Antibody Technique
  • Isomerism
  • Microvilli / chemistry*
  • Microvilli / enzymology
  • Octoxynol
  • Pigment Epithelium of Eye / chemistry*
  • Pigment Epithelium of Eye / cytology
  • Pigment Epithelium of Eye / enzymology
  • Sodium-Potassium-Exchanging ATPase / analysis*
  • Spectrin / analysis*
  • Time Factors

Substances

  • Ankyrins
  • Antigens, Surface
  • Spectrin
  • Octoxynol
  • Sodium-Potassium-Exchanging ATPase