Alveolar type II cell intra-RER protein organization: ferret, more hexagonal structures per the last two posts, there is more order here,  actual linear densities perpendicular to the long axis of the layered granule, and these blend out into the tangential plane as hexagonal structures with a central dense area (either 1 or 2 dots — in this case mostly 1 dot).

Top electron micrograph (unretouched, except to show the bounding box of the inset image) is an enlargement from a negative (9855) of a ferret type II cell, of just one of the layered granules present which is particularly well suited to examination of its tangential-orientation and detection of patterns that might indicate that it is surfactant protein A.

Bottom electron micrograph is inset, enlarged, and the patterning perpendicular to the long axis of the granule layering (here, tangentially cut) is seen, and the erase tool has been used to outline what could be hexagonal patterns for the surfactant protein A 18-mer bouquet.  You are free to decide if this looks right. My question is that they are small, but also would represent just 1/4 of the 100 nm width of the real pattern-period, of mirrored and stacked (4 molecules) of SP-A 18-mers. I have not highlighted all the vertical lines, nor have i highlighted all the hexagonal structures.

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.