title: Calcitonin inhibits proton extrusion in resorbing rat osteoclasts via protein kinase A.
abstract: Although calcitonin is well known to be a potent inhibitor of bone resorption, it remains unknown how it regulates osteoclastic H(+) transport. In this study, we examined the effects of calcitonin on H(+) extrusion in cultured rat resorbing osteoclasts using an intracellular pH (pHi) indicator, BCECF [2'7'-bis-(2-carboxyethyl)- 5-carboxyfluorescein]. Resorbing osteoclasts were identified by their formation of resorbing pits on calcium phosphate-coated quartz coverslips. Both basal pHi and H(+) extrusion activity were significantly higher compared to non-resorbing osteoclasts. Two types of H(+)-extruding systems were identified by pharmacological and immunocytochemical means: a bafilomycin-A(1)-sensitive and an amiloride-sensitive system [H(+) extrusion mediated by a vacuolar type proton pump (V-ATPase) and by a Na(+)/H(+) exchanger (NHE), respectively]. Calcitonin inhibited both H(+) extrusion activities in a dose-dependent manner and this action was mimicked by protein kinase A (PKA) activators, but not by protein kinase C (PKC) activators. Pretreatment with PKA inhibitors completely suppressed calcitonin-induced inhibition, whereas neither PKC inhibitors nor calcium chelators suppressed it. These results indicate that calcitonin inhibits H(+) extrusion generated by V-ATPase and NHE via PKA activation. These inhibitory mechanisms of H(+) transport by calcitonin are important for the regulation of bone resorption.
authors.affiliation: Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Tamura 2-15-1, 814-0193, Sawara-ku, Fukuoka, Japan. kajiya@college.fdcnet.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kajiya
authors.forename: Fujio
authors.initials: F
authors.lastname: Okamoto
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Fukushima
authors.forename: Koji
authors.initials: K
authors.lastname: Okabe
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002116:Calcitonin / Q000494:pharmacology*; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D017494:Proton Pumps / Q000378:metabolism; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002273:Carcinogens; D017494:Proton Pumps; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D005576:Colforsin; D003994:Bucladesine; D002116:Calcitonin; D017868:Cyclic AMP-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate