Visualization of capillaries in skeletal muscle by the ATPase reaction

A simple and reliable technique for the visualization of capillaries in skeletal muscel of dogs, guinea pigs and rats is decribed. 10--20 micrometer frozen sections were incubated in a medium containing Ca2+ and ATP following acid preincubation (pH 3.8--4.2). The capillaries stained in black and were readily seen surrounding the muscle fibers. Serial sections were also treated for alkaline phosphatase. Values for capillary density using both methods were not different.