title: Carbonic anhydrase activity of chick osteoclasts is increased by parathyroid hormone.
abstract: Embryonic chick osteoclasts were harvested, cultured for 18 h, and separated from erythrocytes, and carbonic anhydrase (CA) activity was assayed. Cultures contained 75-85% osteoclasts by acid phosphatase stain. CA activity was also determined after exposure to parathyroid hormone (PTH). Two methods of measurement were used: a delta pH method, which detects the generation of hydrogen ion by carbonic anhydrase, and a mass spectrometric method, which follows the disappearance of 18O-enriched CO2. Unstimulated osteoclasts showed CA activity that was one-third that of erythrocytes but was comparable with macrophages and chondrocytes. Osteoclasts exposed to PTH showed a twofold increase in activity, which occurred after 30 min. Ethoxzolamide (10(-8) M) inhibited enzyme activity by 90%. Treatment of osteoclasts with calcitonin did not prevent the PTH-associated increase in CA activity. The doubling of CA activity with PTH stimulation supports the hypothesis that osteoclastic CA is intimately involved in bone resorption.
mesh_terms: D000818:Animals; D002116:Calcitonin / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002645:Chickens; D004912:Erythrocytes / Q000201:enzymology; D005016:Ethoxzolamide / Q000494:pharmacology; D008264:Macrophages / Q000201:enzymology; D010010:Osteoclasts / Q000187:drug effects / Q000201:enzymology*; D010281:Parathyroid Hormone / Q000494:pharmacology*
chemical_list: D010281:Parathyroid Hormone; D002116:Calcitonin; D002256:Carbonic Anhydrases; D005016:Ethoxzolamide