Hindered diffusion through an aqueous pore describes invariant dye selectivity of Cx43 junctions

The permselectivity (permeance/conductance) of Cx43-comprised gap junctions is a variable parameter of junctional function. To ascertain whether this variability in junctional permselectivity is explained by heterogeneous charge or size selectivity of the comprising channels, the permeance of individual Cx43 gap junctions to combinations of two dyes differing in either size or charge was determined in four cell types: Rin43, NRKe, HeLa43, and cardiac myocytes. The results show that Cx43 junctions are size- but not charge-selective and that both selectivities are constant parameters of junctional function. The consistency of dye selectivities indicates that the large continuum of measured junctional permselectivities cannot be ascribed to an equivalent continuum of individual channel selectivities. Further, the relative dye permeance sequence of NBD-M-TMA ∼ Alexa 350 > Lucifer yellow > Alexa 488 ≫ Alexa 594 (Stokes radii of 4.3 Å, 4.4 Å, 4.9 Å , 5.8 Å, and 7.4 Å, respectively) and the conductance sequence of KCl > TEACl ∼ Kglutamate are well described by hindered diffusion through an aqueous pore with radius ∼10 Å and length 160 Å. The permselectivity and dye selectivity data suggest the variable presence in Cx43-comprised junctions of conductive channels that are either dye-impermeable or dye-permeable.