More tangential sections of RER layered protein from ferret alveolar type II cells seen with electron microscopy. I have chosen one of the more easily identifiable granules with the light portion of the banding ‘periods’ spread out so that any order seen on from the “top down” might be highlighted.  I have outlined in red (this is a “partial erase” in photoshop, against a red (and green) layer), no other manipulation of the micrograph has occurred.

The red outlines are pretty obvious hexagonal structures, seemingly mostly with a central dense area, but way to often for chance, two central dots.  I have seen this so many times that it becomes necessary to call attention to it, and likely it means something in the organization of this surfactant protein (which I am calling surfactant protein A). On the other hand, the size of a ribosomes in these micrographs would make the hexagons a little too small….  maybe only 75- 80 nm across, so this is an issue to reconcile.

Red outlines, within the tangentially spread inbetween layers), green outlines, an area which might be still within this particular RER profile, but might actually be cytoplasmic.  I have compared the incidence of cytoplasmic heaxagonal structures, there are some, no question, and I don’t want to read more into the hexagonal molecular organization than is warranted.  To me however, it is significantly greater within the membrane of the RER when tangentially sectioned as happened here, and the previous post (same animal, same micrograph, same magnification, different site.