Rotary replication of lens gap junctions

We have further characterized the structure of chick lens gap junctions by rotary-shadowed freeze-etch electron microscopy. The crystalline gap junctions, seen in lens epithelial cells and differentiating cells, had connexons arranged in hexagonal clusters separated by particle-free aisles. These connexons measured 7-8 nm in diameter and had center-to-center spacing of 8.5 to 9.5 nm. The noncrystalline gap junctions seen in lens fibers had connexons that were nonordered. Connexons of these gap junctions measured 8-9 nm in diameter and had center-to-center spacing of 8 to 15 nm. Two distinct populations of connexons were seen in these two types of lens gap junctions. One population displayed a central, electron-luscent zone surrounded by six electrondense globules that represented the metal caps of rotary-shadowed subunits of connexons. The second population had a similar ultrastructure but, in addition, contained a central electron-dense core measuring 1.5-2.0 nm that corresponded to the metal cap deposited over the rotary-shadowed central pore of the connexon. This ultrastructure closely resembled that seen previously in rotary-shadowed gap junctions of other epithelial cells and was consistent with the Unwin and Zampighi (1980) model of liver gap junction structure. These results demonstrate that lens gap junctions have the ultrastructure that clearly characterizes gap junctions in other tissues.