A histochemical ATPase method for the demonstration of the muscle capillary network.

A histochemical method for demonstration of the capillaries in skeletal muscle of birds is proposed. The present method, which is a modification of a previously reported myosin ATPase technique used for simultaneous staining of capillaries and fiber types, provides an accurate count of capillaries associated with different fiber types in avian skeletal muscles. We have applied the original and the modified method to serial adjacent sections of certain skeletal muscles and our results show that after the application of the original technique: (a) in muscles having dark Type II fibers, these fibers produce a masking effect on their adjacent capillaries; (b) a consistent and significant undercounting in capillary densities can be seen even in muscles having no dark Type II fibers; and (c) the staining quality and capillary count are substantially improved with the use of the modified method. We attribute the better results obtained with our modification to differences in thermosensitivity of ATPase activity from the capillary endothelium and of the myofibers. A mathematical treatment is therefore proposed to correct the values of capillary count obtained with the original method.