7.7.
VANADIUM SALT STAINS
241
works better than the potassium salt under identical conditions. However,
presumably, the originator of the stain had some reason to think so.
Parsons (1961) suggested using potassium permanganate for block
staining. Tissue fixed in osmium tetroxide was dehydrated in acetone,
and stained for 10-15 minutes in a 1% solution of potassium permanganate dissolved in reagent grade acetone. This was followed by washing
the tissue in a bath of reagent grade acetone containing methyl acrylate
as a reducing agent. This wash was found to be essential to obtain high
contrast in the sections, and also to prevent free permanganate from
interfering with the subsequent polymerization of epoxy resins. Two
drops of methyl acrylate added to 25 ml of acetone, without making any
effort to remove the hydroquinone inhibitor of the former, sufficed. The
methyl acrylate finally was removed by two more baths of reagent grade
acetone before beginning the impregnation process with an epoxy resin.
The illustrations presented by Parsons indicate this to be a fairly
effective general purpose stain. Cytomembrane systems are particularly
evident. But because potassium permanganate is a strong oxidizing agent,
its use before embedding surely is fraught with dangers. Parsons was
aware of this, and commented that if block staining is continued for more
than 20 minutes many RNA granules disappear, and cytomembranes
sometimes become fragmented. He also speaks of "scattered small light
areas in the cytoplasmic matrix of liver cells (which) were suggestive of
the removal of some component." It is likely that these represented spaces
originally occupied by glycogen granules.
7.7. Vanadium Salt Stains
Callahan and Horner (1964) demonstrated the staining abilities of two
vanadium salts which apparently work well with epoxy-embedded tissue.
They are general purpose stains, producing contrast comparable to the
alkaline lead hydroxides. The authors emphasize that there are no
problems with contamination when these stains are used, and this
presumably would be their particular advantage. We have not had
experience with these stains in our own laboratory, however, and therefore I do not know what problems may be encountered in preparing or
handling them.
Hydrated vanadyl sulfate is water soluble. A 1% solution when freshly
prepared makes a satisfactory stain, although it deteriorates in about 2
VANADIUM SALT STAINS
241
works better than the potassium salt under identical conditions. However,
presumably, the originator of the stain had some reason to think so.
Parsons (1961) suggested using potassium permanganate for block
staining. Tissue fixed in osmium tetroxide was dehydrated in acetone,
and stained for 10-15 minutes in a 1% solution of potassium permanganate dissolved in reagent grade acetone. This was followed by washing
the tissue in a bath of reagent grade acetone containing methyl acrylate
as a reducing agent. This wash was found to be essential to obtain high
contrast in the sections, and also to prevent free permanganate from
interfering with the subsequent polymerization of epoxy resins. Two
drops of methyl acrylate added to 25 ml of acetone, without making any
effort to remove the hydroquinone inhibitor of the former, sufficed. The
methyl acrylate finally was removed by two more baths of reagent grade
acetone before beginning the impregnation process with an epoxy resin.
The illustrations presented by Parsons indicate this to be a fairly
effective general purpose stain. Cytomembrane systems are particularly
evident. But because potassium permanganate is a strong oxidizing agent,
its use before embedding surely is fraught with dangers. Parsons was
aware of this, and commented that if block staining is continued for more
than 20 minutes many RNA granules disappear, and cytomembranes
sometimes become fragmented. He also speaks of "scattered small light
areas in the cytoplasmic matrix of liver cells (which) were suggestive of
the removal of some component." It is likely that these represented spaces
originally occupied by glycogen granules.
7.7. Vanadium Salt Stains
Callahan and Horner (1964) demonstrated the staining abilities of two
vanadium salts which apparently work well with epoxy-embedded tissue.
They are general purpose stains, producing contrast comparable to the
alkaline lead hydroxides. The authors emphasize that there are no
problems with contamination when these stains are used, and this
presumably would be their particular advantage. We have not had
experience with these stains in our own laboratory, however, and therefore I do not know what problems may be encountered in preparing or
handling them.
Hydrated vanadyl sulfate is water soluble. A 1% solution when freshly
prepared makes a satisfactory stain, although it deteriorates in about 2