Enzymes that catalyze the hydrolysis of adenosine triphosphate (ATPases) are ubiquitous in the liver, but are present in high concentrations in bile canaliculi (mostly N+,K+-ATPase and Ca2+-ATPase). Their presence can be demonstrated by trapping the released phosphate ions as an insoluble lead salt which can then be converted to dark black lead sulfate.
Within a lobule examine the region around the central vein. Although the anastomosing plates of hepatocytes are unstained, the bile canaliculi of 1 to 2 µm diameter tubes formed by adjacent hepatocytes are intensely stained black. (Additional example).
Bile is secreted into the canaliculi and collects at the periphery of the lobules in bile ductules of the portal triads. (The intense staining of the portal triads makes it impossible to distinguish the bile ductules in this specimen.)