Osmium fixation

The sarcoplasmic reticulum (SR) was first identified as the major mobilizable intracellular store of Ca2+ in skeletal muscles through the work of S. Ebashi, W. Hasselbach and A. Weber (review in Ebashi 1991). Identification of the SR and its role in smooth muscle met some early difficulties, partly due to the destructive effects of osmium fixation. Eventually the SR of smooth muscle was also identified, quantitated and its spatial distribution, peripheral and central, determined (Somlyo et al 1971, Devine et al 1971). Strontium (Sr), used as an electron opaque analogue of Ca2+, permitted direct, electron microscopic visualization of divalent cation transport into the SR (Somlyo Somlyo 1971). 

The preparation of samples for the observation of lipids in foods by both LM and EM involves the chemical fixation of the lipid. For this purpose, the most useful technique is osmium fixation. With this technique, excellent images can be obtained in which the lipids are suitably stabilized by the cross-linking properties... 

The proposed scheme (Fig. 8) also explains why osmium fixation, alone or in combination with glutaraldehyde or (and) permanganate treatment, leads to the classical trilamellar electron microscopic picture of membranes (Fig. 8d). Admittedly, this is not a complete picture of membrane organization after the above treatments. However, if poststaining reveals artifectual detail, the simple trilamellar picture, which incidentally contains the basic information derived from X-ray diffraction, is less misleading. 

Somljo It all depends on the fixation method. We use osmium ferricyanide to selectively infiltrate the SR. If we use intermediate high-voltage electron microscopy, we can look at thicker specimens, and this technique provides more extensive views than obtained from the usual thin sections. This is the same information we get when we infiltrate the SR with Fluo-3. These pictures are pretty reliable. Furthermore, if you want to confirm without chemical fixation, methods such as rapid freezing are available. All these techniques give the same pictures, which vary according to the smooth muscle type. 

Harvested samples should be immediately prepared for the SEM by fixation in a 0.5% osmium tetroxide solution in the dark for 1 h. If the sample is collected in the field, store in buffered 3% glutaraldehyde solution (pH 7.2) until samples can be fixed. 

After glutaraldehyde fixation (Section 3.1 1 2., step 8), fix the cells further with 1% osmium tetroxide, saturated uranyl acetate, dehydrate in an ascending series of ethanol (70, 90, 100%), and embed in epoxy resin. Ultrathin sections of the block, stained with 1% methanolic uranyl acetate and lead citrate, will reveal immunolabeling on the outer surface of the cells... 

To improve the position selectivity in the AD of oligoprenyl compounds bis-cinchona alkaloid ligand 8 was introduced by Corey 15,6]. Its design was based on the [3+2]-cycloaddition model for the AD mechanism, which will be discussed in Section 6E. 1.2. The two 4-heptyl ether substituents of the quinolines are supposed to assist fixation of the substrate in the binding cleft. Additionally, the jV-methylquinuclidinium unit and the linking naphthopyridazine were introduced to rigidify the osmium tetroxide complex of 8 [6],... 

MICROWAVE HEAT-ASSISTED FIXATION WITH OSMIUM TETROXIDE... 

Eggli, P. S., and Graber, W. 1994. Improved ultrastructural preservation of rat ciliary body after high pressure freezing and freeze substitution A perspective view based upon comparison with tissue processed according to a conventional protocol or by osmium tetroxide microwave fixation. Microsc. Res. Technol. 29 11-22. 

After primary fixation the algal and root samples were rinsed in 0.1 M PIPES buffer, pH 7.0, then twice in 0.1 M sodium cacodylate buffer, pH 6.8, and post-fixed in 1% osmium tetroxide in 0.1 M cacodylate buffer, pH 6.8, overnight at 4°C. The osmium solution prepared for the root samples was added with 0.7% potassium ferricyanide in order to improve osmium penetration in the root tissues. This was particularly necessary for the 2 h control roots and roots from RO-treated seed, due to their relatively low water content. The replacement of PIPES buffer with cacodylate buffer before osmication was necessary, as PIPES reacts with osmium, producing a dark precipitate. 

Specialty fixatives, such as Osmium tetroxide, which is used primarily in electron micrography and acetone, is used in fixation of frozen sections. Others used for research purposes on specific tissue, organs or even whole organisms are not discussed in this publication. 

Bland DE, Foster RC, Logan AF (1971) The mechanism of permanganate and osmium tetroxide fixation and distribution of lignin in the cell wall of Pinus radiata Holzforschung... 

Osmium tetroxide, Os04. This is undoubtedly the most important compound or complex of osmium, and it was as the tetroxide that osmium was first separated and, as explained on p. 522, gave its name to the element. It is industrially important both in the fine organic chemicals industry (for the cis hydroxylation of alkenes) and in biological chemistry and medicine for the fixation or... 

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