CONNEXIN43 AND CONNEXIN45 FORM GAP-JUNCTIONS WITH DIFFERENT MOLECULARPERMEABILITIES IN OSTEOBLASTIC CELLS

We examined the expression and function of gap junctions in two rat os teoblastic cell lines, ROS 17/2.8 and UMR 106-01. The pattern of expre ssion of gap junction proteins in these two cell lines was distinct: R OS cells expressed only connexin43 on their cell surface, while UMR ex pressed predominantly connexin45. Immunoprecipitation and RNA blot ana lysis confirmed the relative quantitation of these connexins. Microinj ected ROS cells passed Lucifer yellow to many neighboring cells, but U MR cells were poorly coupled by this criterion. Nevertheless, both UMR and ROS cells were electrically coupled, as characterized by the doub le whole cell patch-clamp technique. These studies suggested that Cx43 in ROS cells mediated cell-cell coupling for both small ions and larg er molecules, but Cx45 in UMR cells allowed passage only of small ions . To demonstrate that the expression of different connexins alone acco unted for the lack of dye coupling in UMR cells, we assessed dye coupl ing in UMR cells transfected with either Cx43 or Cx45. The UMR/Cx43 tr ansfectants were highly dye coupled compared with the untransfected UM R cells, but the UMR/Cx45 transfectants demonstrated no increase in dy e transfer. These data demonstrate that different gap junction protein s create channels with different molecular permeabilities; they sugges t that different connexins permit different types of signalling betwee n cells.