Light and electron microscopic investigation of ATPase activity in musculature during anuran tail resorption

Summary The histochemical activity of adenosine triphosphatase (ATPase) was studied at light and electron microscopic levels in larval tail musculature of Rana catesbeiana and Rana ornativentris during late metamorphic stages. The presence of low, moderate or dark reaction of K₂-EDTA-preincubated Ca⁺⁺-ATPase was correlated with the variable degree of degeneration of white fibres even at the late stage of tail resorption. The reasons for an increase in this ATPase activity in degenerating white muscle fibres are discussed. Irrespective of the degree of degeneration, all red fibres showed high ATPase reaction. During myocytolysis, it is shown that the SR vesicles accumulate electron dense amorphous material. The degree of myofibrillar disintegration correlated with decrease in ultrastructural reaction product for Mg⁺⁺-ATPase. Although grouped atrophy of muscle fibres (as seen in Xenopus laevis, den Hartog Jager et al., 1973, 1975) was absent in musculature of resorptive tails, ultrastructural characteristics including proliferation of SR and dilation of its vesicles represent alteration of the normal neural influence on the skeletal muscle fibres.