We will compute homogenized limits for the diffusion of second messengers in the Ros Outer Segments (ROS) of vertebrates, in visual transduction, when spike--like incisures are presents in the receptors discs. The layered structure of the cytoplasm and the presence of incisures, present topological limitations to compactness. We will present an homogenization limiting procedure based on extension of functions with concave modulus of continuity.

We discuss also the physiological significance of the incisures and present a spectrum of numerical simulations.