Activity of alkaline phosphatase in rat skeletal muscle localized along the sarcolemma and endothelial cell membranes.

Alkaline phosphatase (AP), a membrane-associated glycoprotein which enhances the hydrolysis of monophosphate esters at alkaline pH, is widely distributed in animal tissues. AP activity is increased in a variety of muscle disorders, i.e., myopathies and denervation. Established histochemical methods at the light microscopy level failed to demonstrate AP in skeletal muscles. In the present study we applied the Gomori lead nitrate method for ultrastructural examination of AP in rat gastrocnemius muscles and showed that the enzyme was linked to the sarcolemma of the striated muscle and to the membranes of endothelial cells in adjacent capillaries. In comparison with ATPase activity, AP activity was inhibited by both levamisole and a pH of 7.2, but not by ouabain. Hence, it appears that in skeletal muscles AP is active at a high pH and is bound to cell membranes.