Regulation of cytosolic free calcium in isolated rat osteoclasts by calcitonin.
It is now established that calcium is a second messenger mediating the action of calcitonin on the osteoclast. We have demonstrated that an increase in the concentration of intracellular free calcium ([Ca2+]i) is associated with (and possibly mediates) the functional effects of calcitonin, including an acute reduction of cell spread area (the R effect) and, in the longer term, a reduction in enzyme release. The present study addresses questions relating to mechanisms of calcitonin action on osteoclast [Ca2+]i. We have used asusuberic(1-7) eel and human calcitonin as agonists, and an indo-1-based dual-emission microspectrofluorimetric method for the measurement of [Ca2+]i in single osteoclasts. Whilst asusuberic(1-7) eel calcitonin caused a biphasic increase in [Ca2+]i, human calcitonin produced only a monophasic [Ca2+]i response of a much lower magnitude. Each biphasic response consisted of a rapid initial transient increase, occurring within seconds of exposure, followed by a sustained increase in [Ca2+]i. The magnitude of the latter response was more variable, but was consistently below the peak value of [Ca2+]i. The sustained phase of the calcitonin effect was abolished in extracellular Ca(2+)-free medium. This phase is therefore dependent on extracellular [Ca2+] ([Ca2+]e) whilst the rapid transient increase appeared to be dependent on Ca2+i redistribution. The effects of calcitonin on [Ca2+]i were concentration-dependent, with neither latency nor oscillations. Repetitive 30-s exposures to calcitonin failed to produce subsequent responses. There was a marked concentration-dependent correlation between changes in osteoclast [Ca2+]i and the magnitude of the R effect. Thus the likely components of the biphasic [Ca2-]i response are a rapid redistribution followed by the transmembrane flux of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Moonga
B S
BS
Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London.
Alam
A S
AS
Bevis
P J
PJ
Avaldi
F
F
Soncini
R
R
Huang
C L
CL
Zaidi
M
M
D000818:Animals; D002116:Calcitonin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects / Q000502:physiology; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013050:Spectrometry, Fluorescence
D002116:Calcitonin; D002118:Calcium