SPECIFIC PERMEABILITY AND SELECTIVE FORMATION OF GAP JUNCTION CHANNELS IN CONNEXIN-TRANSFECTED HELA-CELLS

DNAs coding for seven murine connexins (Cx) (Cx26, Cx31, Cx32, Cx37, C x40, Cx43, and Cx45) are functionally expressed in human HeLa cells th at were deficient in gap junctional communication. We compare the perm eabilities of gap junctions comprised of different connexins to iontop horetically injected tracer molecules. Our results show that Lucifer y ellow can pass through all connexin channels analyzed. On the other ha nd, propidium iodide and ethidium bromide penetrate very poorly or not at all through Cx31 and Cx32 channels, respectively, but pass through channels of other connexins. 4,6 Diamidino-2-phenylindole (DAPI) dihy drochloride shows less transfer among Cx31 or Cx43 transfectants. Neur obiotin is weakly transferred among Cx31 transfectants, Total junction al conductance in Cx31 or Cx45 transfected cells is only about half as high as in other connexin transfectants analyzed and does not correla te exactly with any of the tracer permeabilities. Permeability through different connexin channels appears to be dependent on the molecular structure of each tracer, i.e. size, charge and possibly rigidity. Thi s supports the hypothesis that different connexin channels show differ ent permeabilities to second messenger molecules as well as metabolite s and may fulfill in this way their specific role in growth control an d differentiation of cell types. In addition, we have investigated the function of heterotypic gap junctions after co-cultivation of two dif ferent connexin transfectants, one of which had been prelabeled with f luorescent dextran beads. Analysis of Lucifer yellow transfer reveals that HeLa cells expressing Cx31 (beta-type connexin) do not communicat e with any other connexin transfectant tested but only with themselves . Two other beta-type connexin transfectants, HeLa-Cx26 and -Cx32, do not transmit Lucifer yellow to any of the alpha-type connexins analyze d. Among alpha-type connexins, Cx40 does not communicate with Cx43. Th us, connexins differ in their ability to form functional heterotypic g ap junctions among mammalian cells.