EFFECTS OF PHENAZINE METHOSULFATE IN HISTOCHEMISTRY

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Abstract
The histochemical reaction for lactate dehydrogenase (LDH) produces a pattern of dark (Type 1) and light (Type II) fibers in skeletal muscle. The addition of phenazine methosulfate (PMS) to the LDH incubating medium causes a reversal of this pattern. However, potassium cyanide in the incubating medium prevents PMS from suppressing the Type I fiber. It was speculated that PMS promotes electron transfer to cytochrome oxidase, thus bypassing the tetrazolium acceptor and decreasing the amount of formazan deposition. When cytochrome oxidase is low in an area (as in the Type II fiber) or when cytochrome oxidase is inhibited by cyanide, PMS then transfers the electrons to tetrazolium and the deposition of formazan increases. PMS is therefore required in the histochemistry of skeletal muscle in order to increase visualization of LDH in Type II fibers. However, the concomitant use of cyanide then becomes necessary to prevent the suppression of formazan deposition in Type I fibers caused by the PMS.