Expression of Gap Junction Protein in Liver and Lens Fiber Tissue

Abstract

Gap junctions have been found in almost all mammalian tissues except hematopoietic cells, some adult nerve cells, and skeletal muscle cells. They are composed of protein subunits which form hemichannels (con-nexons) in plasma membranes. The hemichannels in the plasma membranes of adjacent cells must recognize each other and undergo a conformational change in order to form a pore through adjacent membranes. Ions and metabolites of a molecular weight < 900 daltons can diffuse through these pores directly from one cytoplasmic compartment to that of the neighboring adherent cell [1,2]. Gap junctions can be recognized on electron micrographs because they form plaques of closely aggregated intermerabraneous particles which show a characteristic septilaminar pattern in cross sections of apposing, negatively stained membranes. These lattice-like structures (plaques) can be purified from liver plasma membranes by differential centrifugation, since plaques do not disaggregate in the presence of non-ionic detergents under conditions where most of the other components of plasma membranes are dissolved. Unwin and Zampighi [3] analyzed the structure of isolated gap junction plaques from rat liver by electron microscopy using Fourier and image reconstruction techniques.