Alveolar type II cell, Dog: granules that might be surfactant protein

Electron microgaphs of lung, Layered intracisternal protein granules in mammalian lung, Ultimate order, the cell

Going back over 114 micrographs of alveolar type II cells in the lungs of dogs (n=9; mostly controls from other experiments or ozone treated, taken expressly for lung morphology looking for ICBs) I found several reasonable occurrences which are montaged here. These images are cropped from micrographs of various magnifications, and while I did enhance contrast on some light ones, no dust and scratches or other photoshop applications were used.  There are some pretty nasty micrographs here, but this is an unbiased sampling of all the ICBs that I found in all the dog tissues that I had photographed in the 1980s.  At least three fixation fluids were used: Modified Karnovsky’s, a glutaraldehyde paraformaldehyde mix, and direct osmium.  It seems that the direct osmium preserved the periodicity in the granules better than the aldehydes, but the micrographs were not as informative overall. White arrows point to the granules (ICBs).  Only in two micrographs were the granules seen in parallel RER profiles, one with 2 stacks and one with 3.

dog_ICB_numerousThe most important observation here, aside from the more central dense line in the granules, is there apparent increased density on the limiting RER membranes, the paucity of ribosomes from the parallel edges, the presence of ribosomes on the leading edges, and a very easy to see “rigidity” to the whole granule when compared to other nearby RER profiles which have variable widths , and also NO central or multiple parallel densities within. Also, a fixed width to the type II cell granule (ICB) appears to be roughly equivalent to about 4 or 5 ribosomes (nearby on the same image) still seems to be about 100nm, and counting the periodicity in the middle and upper and lower densities along the long axis of the granule might be about 7 dots per 100 nm, which actually gives the protein within and the linear periods in both x and y axes similar dimensions: 7 bands high, 7 periods in length.  One would be remiss not to mention that tubular myelin is kind of a “square tubular lattice” so there might be a connection.