Simulation of the ephaptic effect in the cone-horizontal cell synapse of the retina

The drift-diffusion (Poisson--Nernst--Planck) model---including a numerical model for cell membranes that resolves surface-charge boundary layers---is applied to the cone--horizontal cell synapse in the outer plexiform layer of the retina. Numerical simulations reproduce the experimental calcium current-voltage (IV) curves for the goldfish retina in response to a bright spot, with and without an illuminated background. The ephaptic (electrical) effect is demonstrated by computing the shift in the IV curve for background off versus background on for increasingly narrower openings between the sides of the cone and the horizontal cell.