A cytochemical study of the dehydrogenases of mitochondria and mitochondrial particulates by a monotetrazolium-cobalt chelation method

Assessment of immunocytochemical techniques with particular reference to the mixed-aggregation immunocytochemical technique

Antibody-mediated assays are believed to be the most sensitive and specific techniques for antigen localization available to date, but they need extensive controls if specific and quantitative results are to be obtained. Problems arise from both the antibody source and the antigen in the tissue preparation. Specificity of the antibody is often difficult to prove in any direct or indirect antibody technique. When markers are coupled to antibody, binding and diffusion properties of the antibody are changed. Diffusion of antigen from its site and loss of antigenic determinants due to procedures for preserving morphology are two other main problems. The mixed-aggregation immunocytochemical technique provides another way of checking the selectivity of the antibody, since a cross-reactive antigen introduced into the section and not the antibody itself is what is seen. Quantitative studies using localization of lactic dehydrogenase isoenzymes in human skeletal muscle fibres show that the technique fulfils most of the present criteria on precision, specificity and validity for determination of enzymes. It also ensures that more than 80% native antigen in frozen sections is fixed and is two to three times more sensitive and selective than the direct antibody technique.

Formalin fixation in the cytochemical demonstration of succinic dehydrogenase of mitochondria

A variety of established methods for protecting mitochondria were tested on rat duodenal epithelium during the histochemical assay for succinic dehydrogenase. The use of sucrose at isotonic or hypertonic concentrations, 7.5 per cent polyvinylpyrrolidone, divalent cations, physiological salt solutions, phenazine methosulfate, coenzyme Q₁₀, and menadione failed to improve the quality of the histochemical preparation once fresh frozen sections were prepared. However, preservation of mitochondrial integrity with little diminution in succinic dehydrogenase activity was obtained by fixing tissue slices (less than 1 mm. in thickness) in 8 per cent unneutralized, aqueous formaldehyde from 8 to 16 minutes at from 5° to 10°C. prior to freezing. To offset the inhibition of enzymatic activity it was necessary to extend the incubation period by 10 to 15 minutes. Two-micron-thick sections were easily obtained from the frozen blocks of such fixed tissue and incubated in the unmodified Nitro—BT-succinate medium. Once the optimum conditions for fixation of intestinal epithelium were determined, many other tissues were subjected to the same procedure. From the morphological standpoint the appearance of the mitochondria in these histochemical preparations compares favorably with the results obtained using the classical Regaud iron-hematoxylin staining procedure. With most tissues, the results are superior to those with fresh frozen sections. However, results with muscle, sperm, and kidney tubular epithelium are not as strikingly improved as with gut and liver.

Some effects of tetrazolium salt on the metabolism of mitochondria isolated from Jerusalem artichoke tubers

A series of tetrazolium salts were found to accept electrons more readily from succinate than malate even though the rate of oxygen uptake was similar with both substrates. This difference was explained by showing that all the tetrazolium salts tested caused a reduction in electron flow between NAD(+) and Cyt.b. The tetrazolium salts were also found to be able to uncouple phosphorylation from electron transport. The monotetrazolium salts causing complete uncoupling around 100 μmoles/litre and the ditetrazolium salts causing complete uncoupling around 20 μmoles/litre.