REGULATION OF OSTEOCLASTIC ACID-SECRETION BY CGMP-DEPENDENT PROTEIN-KINASE

Nitric oxide (NO) down-regulates osteoclastic activity. The mechanism is unknown, although, in some cells NO acts by stimulating guanylate c yclase which activates cGMP-dependent proteins. We demonstrated cGMP-d ependent protein kinase in osteoclasts by immunofluorescence microscop y. Specificity was confirmed by Western blot analysis showing a single 78 kDa band, the size of the Type I isoform, in isolated avian osteoc lasts. Osteoclast function centers on HC1 secretion at a specialized m embrane organelle. We found that purified cGMP-dependent protein kinas e inhibits ATF-dependent acid transport in reconstituted osteoclast me mbrane vesicles >90%, while cAMP-dependent kinase catalytic subunit, c almodulin kinase II, or cGMP alone were ineffective. This novel, direc t modulation of acid transport by cGMP-dependent kinase and the occurr ence of the enzyme in osteoclasts suggest that a mechanism of NO-regul ation of bone turnover is via cGMP and cGMP-dependent protein kinase i nhibition of HC1 transport. (C) 1994 Academic Press, Inc.