It seems to me that there is a pattern of thickness  changes(width or height if you wish… because of the orientation of the diagrams below) and the rigidity of the plasmalemma inherent in the desmosome (likely due to the transmembrane parts of desmoglein and desmocollin ) and that rigidity includes a specific intercellular space dimension. I have seen this published at about 34-38 nm (that is, from the inner leaflet of the plasmalemma of one cell to the inner leaflet of the plasmalemma of the adjacent cell) to be something on the order of 38 nm.  Using that dimension, if i measure from inside plasmalemma of one cell to the adjacent cell and compare that to the width from the same places in the 200 nm ring or annulus around the desmosome there is going to be a change in the dimensions (which i could measure as just a few nm greater than that within the area of the desmosome proper. And, then a reduction in the intercellular width (per the more routine proximities of two cells) which becomes something like 40 nm.

Here is an article which suggests some dimensions for the desmosome, but does not address adjacent variations in the plasmalemmae including the anulus.  You can compare with two images and measurements below. Keep in mind that the two images below are not derived completely randomly, as I picked two which had substructure which was clear enough to measure.  The annulus of these two desmosomes is indistinct, and longer than that seen in other desmosomes. This likely relates to the plane of section on a perpendicular axis of a round desmosome and surrounding annulus (the latter being increasingly seen as one sections nearer the periphery of the actual desmosome).

top diagram shows a length of two adjacent plasmalemma, measurements relative to that image, bottom one is a different desmosome, notice brown lines for intermediate filaments, black line for length of the desmosomal spot, dotted lines at periodicities of the bridges between desmocollins and desmogleins, outer dense line with dots, periodicities of the extracellular membrane anchor, pink bracket, thickness of the desmosomal intracellular elements, which includes proteins of the intracellular anchor (desmocollins and desmogleins) plakoglobin, plakophilin, desmoplakin and intermediate filaments (visible at the desmosomal-mitochondrial tether on the bottom more clearly than the desmosomal-mitochondrial tether seen at the top of the lower micrograph.  While a big deal is made of the inner and outer dense plaques of the intracellular part of the desmosome, the lower portion of the lower micrograph doesn’t make that case.  Were the micrograph sectioned end on to the intermediate filaments below, there might be a more visible inner dense plaque.  The outer dense plaque (plakophilins, plakoglobin portion and desmoplakin proteins) is well defined. NB, there is a “flatness” or “rigidity to the outer mitochondrial membrane where the intermediate filaments lie beside it… i hope to search for proteins that might be involved in the linking of mitochondria and intermediate filaments.

I havn’t read much (or found much to read) about the making – breaking – moving – adjusting of desmosomes, or the energy requirement for desmosome modification, but it seems too much a coincidence that mitochondria would be closely tethered to desmosomes and not provide this function. That said, they have been photographed by me in mouse, rat, neonatal rat, ferret, hamster, syrian hamster, dog, and guinea pig, just to name a few in the list that I have looked at in the last weeks. And they are so similar in all, that so far, if i list one image of a desmosomal-mitochondrial junction from one species I cannot tell it from another. This is good, i guess, but it would be more interesting if the structure showed some variation in structure….. that could perhaps be correlated with differences in the component proteins.

Here is one desmosomal-mitochondrial junction from ferret, which didn’t have a nice even pattern of cadherins in the middle, but did have a punctuated central line…with dots less than 20nm apart…. they seemed a little staggered.  Here is the original micrograph (i removed a scratch in the negative not in the area of the desmosome using photoshop bandaid tool, but it otherwise just a scan of the print. 5940 18648 ferret hepatocyte.

The image below it is an enlargement of the box in top image. Ribosome-red dot for size, and the black lines overlie densities in the intercellular area of the desmosome.

There are several nice things about this micrograph of a desmosomal mitochondrial tether (i.e. tethered via the intermediate filaments of the desmosome). One nice thing is the very rigid, and parallel membrane-leaflet quality of the plasmalemma where there is the desmosomal protein complex, and it also exhibits a very even and well defined separation of the outer and inner leafelets of the plasmalemma (at least this is what i think is shown in the micrograph below).  I have marked the two leaflets on the cell membranes on the adjacent cells with black lines. There are obvious periodicities within the inner and outer membrane leaflets too… not withstanding the density of the lead citrate and uranyl acetate stains and the quality of fixation) which seems to present overall patterning in the entire micrograph. I have marked the extracellular lines (which are not likely to be random as they appear, but more likely to be organized attached wishbone shapes (mirrored vertically and copied horizontally) shown in an earlier post but the lines here have been drown over actual densities in the extracellular (intercellular) space of the desmosome. Green blobs mark periodicities within the two leaflets of the plasmalemma, and the pink blobs mark the densities which are extracellular but likely adjacent, maybe even part of (like the cadherins in desmosomes) those proteins. (green blobs are INTERcellular, the pink blobs are within the plasmalemma (transmembrane). Electron micrograph on left is unretouched, on right, contrast and brightness enhanced and vector overlays show densities which can be matched to image on the left. This stub-tail monkey hepatocyte came from an animal that received two test doses of perfluorodecalin (a very small amount) a year prior, which in my experience has nothing to do with these tethers. Shown immediately below the outer leaflet of the plasmalemma is what appears to be a regular compartmentalization (shown as rectangles) likely representing a highly structure arrangement of plakophilin and plakglobin and maybe some desmoplakin and a bit of vimentin.  The number of densities (green or pink, and likely connected parts of the cadherin dimers, turn out in this micrograph to be about 9 nm…  a little close than found in mouse micrographs so far. 

This is just a micrograph to justify the idea that the desmosomal mitochondrial tethering, or junction or des-mites as i have aptly named them (as opposed to pore-mites) for nuclear pore mitochondrial tethering, are pretty universal. Here a single tether is in a stub tail monkey hepatocyte, from tissue taken back in the 1970s while studying the effects of infusing artificial blood emulsions (perfluorochemical based blood substitutes) . This particular monkey (Maccaca speciosa, probably female) did receive two test doses of a perfuorodecaline emulsion, just a tiny amount, 0.05cc/kg of a 10% emulsion PP5ct and 5% F68) (Lee Clark Jr named all his emulsions, this was EM#750428). no perfluorochemical droplets were seen in this hepatocyte. Sac date was 5 10 76.

So desmosomal mitochondrial junctions are here. Mitochondrion is in top part of micrograph, desmosome is attached to the down pointing portion.

Here is another pseudocolored desmosome with portions of two mitochondria top and bottom parts of this electron micrograph. It was difficult to determine exactly where the plasmalemma from each of these two cells went at the point of the desmosome, but I thought long and hard about which part of the structure they were. It seemed to me that there was a slight electron lucency just under the plasmalemma on each side, therefore this is the way I pseudocolored (with pink) the cell membranes.  The densities within the desmosome itself looks like there are three rows… the central dotted (periodic) line where the cadherin molecules knot together (my guess is this is a totally symmetric arrangement, not at all random like suggested by some) and perhaps another periodicity (well not perhaps…. it is pretty striking) which lies a little separated from the plasmalemma.  I don’t know if any of the models of the cadherins show a “lump” structure before the transmembrane part… ? That will take some searching.

Top image is unretouched transmission electron micrograph of a desmosome, as mentioned, mitochondria portion seen top and bottom.  The box in this image is what is enlarged in the second image. There are two very prominent intramitochondrial granules, especially the one in the mitochondria at the bottom of the micrograph.
This image is from the boxed area above, thus enlarged, pink is the plasmalemma, orange is the area just under the plasmalemma of each cell and into the space of the desmosome. Blue is what I see as the possible densities of cadherin molecules.

In this inset the periodicity of the outer part of the desmosome (probably still cadherin molecules) is a spacing about 1/15nm  not too different from that found in a previous post at something around 1 density for each 13-14nm spacing.  The periodicities on the central dense line of the desmosome in this micrograph might be something around 18nm spacing… I would have preferred if the densities came out one-to-one, but anticipate that in other assessments that it might do just that. But for now, i just count what shows up. 6102_5070_mouse_female_control.