Simulation Of Particle Diffusion Across Gap Junction Channels Based On Their Pore Geometry Explains Unidirectional Fluxes

Abstract

Connexin proteins form gap junction channels that allow intercellular communication with distinct perm-selectivity properties. Mono-heteromeric and heterotypic combinations of cardiac connexin43 (Cx43) and Cx45 induce a preferential flux based on molecular size. For Lucifer Yellow or Rhodamine123, preferential flux was 3x larger from homomeric to heteromeric connexons. For heterotypic combinations, fluxes from homomeric Cx45 to homomeric Cx43 connexons were 4x larger. This favored direction was not expected. Our objective was to use computational simulation of particle diffusion across gap junction channel pores to find if geometrical parameters can explain our in vitro permeability data.HeLa cells were stained with red or green dyes to differentiate expression and co-cultured on glass cover-slips for 8 hours. A Nikon epifluorescent Eclipse7000 microscope helped quantifying diffusion. Fluorescent dyes were iontophoretially injected into a single red cell surrounded by green cells. Coupling coefficient (cells touching the injected cell/touching cells with dye) was determined 3 min after.3D geometric model of the pore was mathematically modeled combining cylinders, cones and an ellipsoid. Particle position, velocity, acceleration and force vectors were calculated after every time step (10-14 s), considering wall-particle and particle-particle elastic interactions, inter-particle electrostatic, Brownian and other forces. Particles' paths were recorded and those crossing the pore were counted. Without electric field, number of particles crossing increased linearly as mouth radius increased. With an electric field, number of particles crossing varied non-linearly with a maximum when radius was around 21.4 A.Our computer simulations predict that changes in phosphorylation, voltage or connexin recombination yield to changes in pore structure which in turn affects large molecules' permeability.