mitochondrial volume

Dean Pentcheff dean2 at tbone.biol.scarolina.edu
Thu Sep 23 17:13:13 EST 1993


brambl at graz.cbs.umn.edu (Robert Brambl) writes:
>rogersh at uk.ac.afrc wrote:
>> Subject: mitochondrial volume
...
>>  How would one go about determining the mitochondrial volume in
>> tissue culture cells....unfortunately plant ones.
...
>Measuring mitochondrial volume in vivo can be tricky, since mitochondria  
>may change shape, fuse, shrink, or swell, depending upon physiological  
>conditions.  Nevertheless, if you can hold all these things constant, I  
>would suggest using potentiometric cyanine dyes for the mitochondria.   
>These work beautifully in plant cells.  See Plant Physiol. (1987)  
>84:1385-1390. You could photograph the fluorescent mitochondria, enlarge  
>the prints suitably, and use area measurements to *estimate* mitochondrial  
>volume.
>
>Hope this helps. 

Just to throw my two cents in yet again...

Does this technique involve measuring the area covered by intact
mitochondria?  Or is it a technique for staining the mitochondria for
identification in sections.  If the latter, it sounds great (you can't
measure what you can't identify).

If the former, then there's a serious problem.  You can't get an
estimate of mean particle volume by looking at two dimensional
projections of three dimensional particles unless (a) the particles are
convex without any concavities; and (b) you have a precise mathematical
model of the particles' shape.  Consider two cases.  Case one is the
volume of projected spheres.  There, you can easily calculate volume
from projected area, since you know there are no hidden cavities, and
you have a precise model of the shape.  Case two is the volume of birds
photographed in flight.  What's the wing orientation?  Are they even
extended?  How much of the bird is aligned in the line of sight, and
hence invisible, as compared with the projected area?  The answer
you'll calculate from such an approach will be wrong - it will have
high variance among birds due to orientation differences, and it will
be badly biassed because the bird volume estimate will not account for
concavities.

Mitochondria ("mito-" = thread!) are notoriously non-convex and
non-modelable in shape.  Measuring volume by projection would be a bad
idea here, particularly considering that there are good new
stereological ways to estimate particle volumes.  The new approaches
are mathematically known to be unbiassed (provided you can identify
your objects!) and are relatively easy to perform (compared with
classical stereological approaches to particle size).

-Dean
-- 
N. Dean Pentcheff 
Biological Sciences, Univ. of South Carolina, Columbia SC 29208 (803-777-8998)
Internet addresses: pentcheff at pascal.acm.org or dean2 at tbone.biol.scarolina.edu



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