Gap Junctions in Liver: Isolation, Morphological Analysis, and Quantitation

Gap junctions are arrays of cell-to-cell channels that permit exchanges of cytoplasmic low-molecular-weight constituents, such as ions and various metabolites. This chapter focuses on the liver gap junctions. X-ray diffraction and image reconstruction based on low-dose electron microscopy, in combination with the other techniques, indicate that each gap junctional channel comprises two halves, one through the membrane of each adjacent cell. Each connexon is composed of six apparently identical polypeptide chains, probably associated with phospholipid. Gap junctions consist of large arrays of closely packed connexon pairs, which retain their integrity under a variety of experimental treatments. The chapter discusses the isolation of gap junctions as applied to a specific tissue, the rat liver, with emphasis on techniques that have found to provide reproducibly good yields of highly enriched gap junction fractions. The most commonly used and simplest technique for examining gap junction fractions is to use negative stain.