So-called annular gap junctions in bone cells of normal mice.

Spherical bodies consisting of a granular matrix and a pentalaminar limiting membrane were found in cells from the proximal tibial metaphysis of normal mice. The structures measured about 280-570 min in diameter and were located mainly in the cytoplasm of osteoblasts and occasionally in preosteoblasts. The granules within the bodies resembled ribosomes. The multi-layered composition of the limiting body membrane was identical with that of intercellular gap junctions.