A STUDY OF INTERCELLULAR RELATIONSHIPS BETWEEN TRABECULAR BONE AND MARROW STROMAL CELLS IN THE MURINE FEMORAL METAPHYSIS

The cellular relationship between the substantia spongiosa of bone (ca ncellous or trabecular bone) and the haematopoietic bone marrow in the femoral metaphysis of C57BL/6NJCL mice was studied by transmission el ectron microscopy (TEM). Special attention was directed to intercellul ar junctions between osteocytes, osteoblasts, and bone marrow reticula r cells. These were gap junctions and adhesive devices of simple archi tecture referred to as primitive junctions or zonula adherens-like jun ctions. Gap junctions were observed between osteocytes (within the tra beculae) and osteoblasts (at the trabecular surface) and between osteo blasts and marrow reticular cells. Gap junctions were also observed be tween the same cell type within each of these categories. These juncti ons involved the plasmalemmal membranes of adjacent cell bodies and of processes. Primitive cell junctions had a similar cellular distributi on. Quantitative analysis of the cell types covering or positioned aro und the trabecular bones and of gap junctions between these and other cells was carried out by TEM. It was found that osteoblasts were the m ost numerous cell type, occupying 31% of the total of each cell type p ositively identified around the trabeculae (31%), while pre-osteoblast s, (flattened bone marrow reticular cells) took up 26%. These data emp hasise the intimate relationship of the various mesenchymal cells base d on processes and intercellular junctions, and point to an anatomical and probably functional integration of trabeculae and marrow. The fun ctional significance and putative regulatory activity of this unit are discussed.