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Different calcium sensitivity in osteoclasts on glass and on bone and maintenance of cytoskeletal structures on bone in the presence of high extracellular calcium
Author(s) -
Lakkakorpi Päivi T.,
Lehenkari Petri P.,
Rautiala Timo J.,
Väänänen H. Kalervo
Publication year - 1996
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199609)168:3<668::aid-jcp19>3.0.co;2-v
Subject(s) - microfilament , bone resorption , extracellular , resorption , calcium , osteoclast , chemistry , cytoskeleton , microbiology and biotechnology , multinucleate , biophysics , endocrinology , in vitro , biology , biochemistry , cell , organic chemistry
The sensitivity of rat osteoclasts to increased extracellular calcium concentrations ([Ca 2+ ] e ) was investigated by single cell measurements of free cytosolic calcium concentrations ([Ca 2+ ] i ), by changes in microfilament organization of resorbing osteoclasts, and by in vitro bone resorption assays. Osteoclasts cultured on glass and on bone showed clear differences in their responses, as in 44% and 52% of osteoclasts on glass but in only 21% and 25% of osteoclasts on bone [Ca 2+ ] i increased when [Ca 2+ ] e was increased from 2 mM to 6 or 10 mM via perfusion, respectively. Bone resorption was inhibited without changes in the osteoclast numbers only by 10 mM [Ca 2+ ] e in 2 day cultures. Furthermore, there were no changes in the organization of microfilament structures in resorbing osteoclasts after increased [Ca 2+ ] e (up to 20 mM [Ca 2+ ] e , 30 min incubation). These results suggest that the sensitivity of osteoclasts to increased [Ca 2+ ] e is dependent on their activation phase (resting/migrating vs. resorbing) and that resorbing osteoclasts are not sensitive to increased [Ca 2+ ] e or that the sensing system cannot be reached in polarized resorbing osteoclasts. In contrast, increasing [Ca 2+ ] i through the use of calcium ionophores dispersed specific microfilament structures at the sealing zone transiently in a few minutes. This shows that [Ca 2+ ] i is used as a signaling mechanism to inactivate osteoclasts, with a similar end result on microfilament structures at the sealing zone as caused by increased concentration of cAMP and activation of protein kinase C. © 1996 Wiley‐Liss, Inc.