Figure 3: Rat lungs. Postnatal day 3. Methacarn fixation. Immunolocalisation of different markers, carried out in adjacent sections. Standard ABC method. Haematoxylin counterstaining. s: saccule; c: canalicular portion of respiratory space; v: vessel. Bar 20m. (a) -SMA immunolocalisation. Besides what found in the vascular wall, a strong labelling is found in the myocytes adhering to the epithelium in the canalicular portions of respiratory spaces, as well as in cells located in the intersaccular walls. (b) PDE5 immunolocalisation. The labelling is restricted to the cytoplasm of several stromal cells, located in close proximity with the saccular boundary. The myocytes of the small vessel and of respiratory channels are unstained. (c) desmin immunolocalisation. Both the myocytes in the canalicular portions of respiratory spaces and those belonging to the vessel wall are strongly labelled; moreover few labelled cells are scattered in the intersaccular walls. Arrows indicate some α-SMA- or desmin-containing PDE5-positive cells.