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.