title: Heparan sulphate proteoglycans on rat parathyroid cells recycle in low Ca2+ medium.
abstract: A rat parathyroid cell line, with some differentiated properties of the parathyroid gland, synthesizes predominantly a heparan sulphate proteoglycan (HS-PG) typical of cell surface HS-PGs (core protein = approximately 70 kDa, three to four HS chains of approximately 30 kDa). A 10 min pulse-chase protocol was used to determine the metabolic fate of the HS-PGs for cells maintained in 2.1 mM-Ca2+ (high Ca) or in 0.05 mM-Ca2+ (low Ca). In low Ca, approximately 60% of the labelled HS-PGs reach the cell surface (t1/2 = approximately 15 min) as determined by trypsin accessibility. This population of HS-PGs recycles (t1/2 = approximately 9 min) between the cell surface and an intracellular (presumably endosome) compartment. After approximately 2 h, this population of HS-PGs is internalized and rapidly degraded in lysosomes. In high Ca, only approximately 10% of the HS-PGs reach the cell surface, where they do not recycle. Changing from high to low Ca any time between 30-120 min of chase, rapidly (t1/2 less than 4 min) redistributes the HS-PGs to the cell surface where they begin recycling; conversely, changing from low to high Ca leads to a rapid sequestration of the cell surface HS-PGs within the cells. Other divalent cations fail to mimic the response to Ca2+. The results suggest that most of the HS-PGs in this cell line are anchored in a membrane compartment involved in a transport process between endosomes and the cell surface which is regulated by the concentration of extracellular Ca2+.
authors.affiliation: Bone Research Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Y
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: K
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: M
authors.initials: M
authors.lastname: Yanagishita
authors.forename: V C
authors.initials: VC
authors.lastname: Hascall
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D011508:Chondroitin Sulfate Proteoglycans / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000378:metabolism*; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D008954:Models, Biological; D010280:Parathyroid Glands / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D014357:Trypsin / Q000378:metabolism
chemical_list: D002118:Calcium; D011508:Chondroitin Sulfate Proteoglycans; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D014357:Trypsin