Amylin inhibits bone resorption by a direct effect on the motility of rat osteoclasts.
We have performed a set of independent studies on the effects of the circulating pancreatic polypeptide, amylin, on rat osteoclast function, in vitro. Time-lapse video observations, measuring cell protrusions and retraction, showed that 250 nmol l-1 amylin or 250 nmol l-1 beta-calcitonin gene-related peptide (beta-CGRP) inhibited osteoclast motility (quiescence or Q effect). Both amylin and beta-CGRP produced inhibitory responses with a significant first-order regression over time (half-times, 19 and 28 min respectively). In contrast, 250 nmol l-1 amylin or 250 nmol l-1 beta-CGRP produced no change of osteoclast spread area, whilst 300 pmol l-1 calcitonin (CT) application resulted in cell retraction (R effect). Forskolin (10 mumol l-1) mimicked amylin and CGRP in inhibiting osteoclast motility (half-time, 8.6 min), and similarly lacked an effect on cell spread area. Neither amylin nor beta-CGRP (62.5-1250 nmol l-1) elevated cytosolic free calcium levels ([Ca2+]i) in single osteoclasts whilst 300 pmol l-1 salmon calcitonin (sCT) produced a rapid phasic elevation of [Ca2+]i, confirming previous results with asusuberic (1-7) eel calcitonin. The osteoclast-bone resorption assay revealed the following potency difference in direct comparison of the area of resorption per bone slice: beta-CGRP/amylin, 0.1; sCT/amylin, 800 and human CT/amylin, 12. The potency of deamidated amylin approached that of beta-CGRP. Assay precision ranged between 0.3 and 0.8. Amylin (250 nmol l-1) also significantly (P < 0.05) reduced supernatant (tartrate-resistant) acid phosphatase in the bone-osteoclast cultures. These measures independently indicate an effect of amylin on osteoclast motility through mechanisms distinct from those of calcitonin, possibly through different selectivities for receptor subtypes, the cyclic AMP-linked 'amylin subtype' and the [Ca2+]i-linked 'calcitonin subtype'.
Alam
A S
AS
Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London.
Moonga
B S
BS
Bevis
P J
PJ
Huang
C L
CL
Zaidi
M
M
D000682:Amyloid / Q000494:pharmacology*; D000818:Animals; D001862:Bone Resorption / Q000517:prevention & control*; D002116:Calcitonin / Q000494:pharmacology; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D066298:In Vitro Techniques; D058228:Islet Amyloid Polypeptide; D010010:Osteoclasts / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D000682:Amyloid; D058228:Islet Amyloid Polypeptide; C060605:amylinamide; D005576:Colforsin; D002116:Calcitonin; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide; D002118:Calcium