  We study the flow of membranal fluid through a ring of immobile particles
mimicking, for example, a fence around a membrane corral. We obtain a simple
closed-form expression for the permeability coefficient of the ring as a
function of the particles' line fraction. The analytical results agree with
those of numerical calculations and are found to be robust against changes in
particle number and corral shape. From the permeability results we infer the
collective diffusion coefficient of lipids through the ring and discuss
possible implications for collective lipid transport in a crowded membrane.
