Square-array fiber cell membranes in the mammalian lens

Abstract

Two types of intercellular contacts have been observed between lens fiber cells. Gap junctions showing the normal EF-pit/PF-particle fracture pattern have been Identified in a number of species and predominate in the chick where they can cover as much as 50% of the cell surfaces. A second type of junction appears in mammalian lenses and is composed of membranes containing square crystalline arrays. In an effort to further characterize the square array membranes we have compared fragments of intact lenses to isolated junctions and used a variety of freeze-fractureetch procedures to visualize the unusual fracture morphology.Fig. 1A shows a typical fracture pattern of fiber cell membranes in a fragment of intact rat lens cortex. Two fracture surfaces are observed separated by a large step (arrows). The upper surface is covered by large irregularly shaped particles. In the lower membrane surface 8-9 nm dia. particles are clustered in some regions into small square arrays; a few tightly packed clusters appear to be covered by a small plaque of amorphous material (circles).