Structure identification. A. Representative canaliculus suitable for intensity profile extraction. It is straight and uniform, tight junctions are symmetrical, undisrupted and run in parallel. Protein intensity profiles of a length 8 μ m are extracted by measuring the pixel intensities of two channels (Bsep, red, functional marker protein; Zo-1, green, structural marker protein) perpendicular to the canaliculus. For example, one of the possibly extracted profiles is shown by a white line. B. Canalicular regions are extracted using the foreground-background detection function of the Zeta software . Foreground mask of the canaliculus shown in A. White areas are considered for further processing. C. Skeletonization results.