title: Endothelin inhibits osteoclastic bone resorption by a direct effect on cell motility: implications for the vascular control of bone resorption.
abstract: The abundance of endothelin (ET)-producing endothelial cells in bone marrow and the proximity of these cells to bone-resorbing osteoclasts prompted us to evaluate the action of ET-1 on osteoclast function. Osteoclasts disaggregated from neonatal rat long bones were settled onto devitalized cortical bone substrate, and resorption was quantified by morphometry. The supernatant tartrate-resistant acid phosphatase activity was determined by a spectrophotometric method using paranitrophenol phosphate as substrate. Cell motility was quantified by time lapse video- and computer-assisted image processing using an empirical procedure for morphometric analysis. Cytosolic free calcium levels ([Ca2+]i) were measured in single cells by an indo 1-based microspectrofluorimetric method. Using the area of bone resorbed per slice as response, we found that ET-1 caused a significant (P = 0.011) concentration-dependent inhibition of osteoclastic bone resorption (EC50 = 2.5 nM) without inhibiting acid phosphatase secretion. Exposure of isolated osteoclasts to ET-1 also led to a marked concentration-dependent inhibition of osteoclast motility (EC50 = 7.9 nM; P = 0.013; t1/2 = 18 min) without significant effects on cell spread area. These effects of ET-1 were reversible after removing the peptide, and the cells remained viable during the experiments. In addition, ET-1 did not elevate [Ca2+]i at the concentrations tested. The results suggest that ET-1 specifically interacts with an osteoclast receptor to inhibit osteoclastic bone resorption and cell motility. As the concentration of ET-1 required for osteoclast inhibition was similar to that reported for smooth muscle contraction, it is possible that ET-1, produced locally from the bone marrow endothelial cell, might play a primary role in osteoclast regulation.
authors.affiliation: Department of Cellular and Molecular Sciences, St. George's Hospital Medical School, London, United Kingdom.
authors.forename: A S
authors.initials: AS
authors.lastname: Alam
authors.forename: A
authors.initials: A
authors.lastname: Gallagher
authors.forename: V
authors.initials: V
authors.lastname: Shankar
authors.forename: M A
authors.initials: MA
authors.lastname: Ghatei
authors.forename: H K
authors.initials: HK
authors.lastname: Datta
authors.forename: C L
authors.initials: CL
authors.lastname: Huang
authors.forename: B S
authors.initials: BS
authors.lastname: Moonga
authors.forename: T J
authors.initials: TJ
authors.lastname: Chambers
authors.forename: S R
authors.initials: SR
authors.lastname: Bloom
authors.forename: M
authors.initials: M
authors.lastname: Zaidi
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001862:Bone Resorption; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D016232:Endothelins / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000502:physiology; D010010:Osteoclasts / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D016232:Endothelins; D000135:Acid Phosphatase; D002118:Calcium