AJP - Endocrinology and Metabolism, Vol 253, Issue 6 E670-E674, Copyright © 1987 by American Physiological Society
Carbonic anhydrase activity of chick osteoclasts is increased by parathyroid hormone
S. F. Silverton, S. J. Dodgson, M. D. Fallon and R. E. Forster 2nd
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104.
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.
