An ultracytochemical investigation of ouabain-sensitive p-nitrophenylphosphatase in chick osteoclasts.

Cytochemical methods for the demonstration of p-nitrophenylphosphatase (p-NPPase) at the electron-microscopic level were applied to avian osteoclasts to elucidate some of the functional differences among ruffled border, other membrane systems, and cellular organelles. The localization of p-NPPase activity occurred in mitochondria, in lysosomes, and on the cytoplasmic side of the ruffled-border membrane. Enzymatic activity in the ruffled-border membrane was sensitive to ouabain and was partially dependent on potassium. Thus, Na+,K+-ATPase, the proposed sodium pump, appears to be present in the osteoclast ruffled border. The activity in ruffled border occurred only when osteoclasts were attached to bone. Following calcitonin treatment many osteoclasts were detached from the bone surface and lacked reaction product along the ruffled-border membrane. The lysosomal p-NPPase activity was not sensitive to ouabain and was distinct from that of other lysosomal phosphatases. The p-NPPase activity in mitochondria was not inhibited by ouabain but was sensitive to duramycin. The mitochondrial p-NPPase may, therefore, represent the mitochondrial proton pump.