GAP JUNCTIONAL INTERCELLULAR COMMUNICATION CONTRIBUTES TO THE CONTRACTION OF RAT OSTEOBLAST POPULATED COLLAGEN LATTICES

The contraction of native collagen lattices by resident mesenchymal ce lls mimics the organization of collagen during development and repair. Lattice contraction is cell density dependent, suggesting that cell-t o-cell communications may contribute to the process. This possibility was investigated by comparing lattice contraction by four rat osteobla stic cell lines: ROS 17/2.8 cells (ROS); ROS transfected with an antis ense cDNA sequence of the gap junctional protein connexin 43 (RCx16); ROS transfected with connexin 45 cDNA, a connexin not normally express ed in ROS cells (ROS/Cx45); and ROS transfected with cDNA encoding car boxy-terminal truncated Cx45 (ROS/Cx45tr). The cell coupling indices, which reflect gap junctional communication, were quantitated by the fl uorescent dye scrape loading. ROS cells were well coupled (index 3.0), ROS/Cx45tr were better coupled (index 4.2), ROS/Cx45 were poorly coup led (index 1.7), and RCx16 showed no coupling (index 1.1). As determin ed by immunoblotting, the level of connexin 43 protein was increased i n both ROS/Cx45tr and ROS/Cx45 cell lines compared with ROS cells, whi le the level in RCx16 cells was reduced, ROS populated collagen lattic es (PCLs) contracted significantly more at day 5 (177 mm(2) to 67 mm(2 )) than ROS/Cx45tr (84 mm(2)), ROS/Cx45 (108 mm(2)), or RCx16 (114 mm( 2)), Myosin ATPase activity, which is required for lattice contraction , was equivalent in all four cell lines, indicating that it was not re sponsible for inhibiting PCL contraction, ROS cells in collagen appear ed elongated compared with the other cell lines which were more rounde d, These experiments suggest gap junctional communication contributes to PCL contraction by resident osteoblasts.