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D G WALKER

Publications and source records attributed to D G WALKER.

At least 19 recordsLinked to original sources
PubMed1963

The use of formalin fixation in the cytochemical demonstration of succinic and DPN- and TPN-dependent dehydrogenases in mitochondria.

Brief formalin fixation in the cold prior to histochemical assay of rat liver and pancreas for various dehydrogenases has been used successfully to circumvent the structural damage and enzymatic loss to which mitochondria of frozen sections would otherwise be subject. To obtain an optimal result a single set of conditions has been devised, including fixation prior to freezing of minute (finely diced) organ blocks in graded concentrations (0.7 to 2.0 per cent) of formaldehyde in chilled (1-4 degrees C) Hanks' balanced salt solution, freezing at not higher than -70 degrees C, and use of nitro-BT or, preferably, tetranitro-BT. The present histochemical study of hepatic and acinar cells indicates that not only are succinic and D-beta-hydroxybutyric dehydrogenases located exclusively in the mitochondria but so are lactic, malic, and the isocitric dehydrogenases.

Animals↗
PubMed1963

A survey of dehydrogenases in various epithelial cells in the rat.

Several different epithelial elements that have intense active transport or protein secretory functions were histochemically assayed in several dehydrogenase media by a recently perfected method. The mitochondria represented the only site of activity, not only when tested in the succinate and D-beta-hydroxybutyrate media, but also when tested in the lactate, malate, and isocitrate media. The reaction for D-beta-hydroxybutyric dehydrogenase in the mouse kidney was curiously limited to the mitochondria of the distal segment of the proximal convoluted tubule, a finding that most convincingly shows that dehydrogenase activity may be differentiated in certain instances from diaphorase activity by the ditetrazole methods and that D-beta-hydroxybutyric dehydrogenase is not present in all mitochondria. Tetranitro-BT is favored over nitro-BT in studies conducted on most organs prepared without fixation and on formalin-fixed tissues that consist of lipid-containing or active transport cells.

Animals↗
PubMed1961

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 Q(10), 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 degrees to 10 degrees 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.

Animals↗