A new histochemical method for magnesium actomyosin adenosine triphosphatase at physiological pH.

A new lead-precipitation technique for demonstrating magnesium-activated actomyosin adenosine triphosphatase (ATPase) at physiological pH and electrolyte levels in fixed skeletal muscle sections is reported. This method is compared with standard acid- and alkali-denatured muscle stained for calcium myosin ATPase as well as calcium-formalin denatured and pyrophosphate-formalin denatured muscle also stained for calcium myosin ATPase. The technique was developed using hamster skeletal muscle; however, it has also been applied to human, rat, and cat muscle. The fiber-type staining intensities of the formalin-denatured magnesium actomyosin ATPase closely resemble those of the formalin-denatured calcium myosin ATPase in rodents, but intensities in Type 1 fibers are reversed relative to calcium myosin ATPase in human muscle. Cat muscle shows intermediate characteristics.