title: Recycling of transferrin receptors and heparan sulfate proteoglycans in a rat parathyroid cell line.
abstract: We examined recycling of heparan sulfate (HS) proteoglycans and transferrin receptor (Tf-R) in a rat parathyroid cell line. While extracellular Ca2+ concentration ([Ca2+]e) regulates the recycling of HS proteoglycans in parathyroid cells, such that HS proteoglycans only recycle when [Ca2+]e is lowered below physiological levels, recycling of Tf-R occurs equally well both in 0.05 mM (low) and 2 mM (high) [Ca2+]e. Inhibiting endocytosis chemically with phenylarsine oxide or at low temperature (4 degrees C) did not abolish the effects of changing [Ca2+]e on HS proteoglycans in the recycling compartment even though transport of HS proteoglycans from the Golgi complex to the cell surface was inhibited in low [Ca2+]e. Microtubules are not involved in the recycling of HS proteoglycans or of Tf-R since nocodazole did not affect these processes. Inhibiting the increase of intracellular Ca2+ by an intracellular Ca2+ chelator sustained recycling of HS proteoglycans even in the presence of high [Ca2+]e. These observations show that the exocytosis pathway of HS proteoglycans in the recycling compartment is specifically regulated by [Ca2+]e, whereas that for constitutive secretion is not. Therefore, the recycling of HS proteoglycans may be directly related to some functions of parathyroid cells regulated by [Ca2+]e. Although the mechanism by which [Ca2+]e regulates the exocytosis and recycling of HS proteoglycans is uncertain, it is suggested that an increase of intracellular Ca2+ is necessary, but not necessarily sufficient, for inhibiting their exocytosis.
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: M
authors.initials: M
authors.lastname: Yanagishita
authors.forename: V C
authors.initials: VC
authors.lastname: Hascall
mesh_terms: D000345:Affinity Labels; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004705:Endocytosis; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D015739:Nocodazole / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism*; D051381:Rats; D011990:Receptors, Transferrin / Q000378:metabolism*; D014357:Trypsin
chemical_list: D000345:Affinity Labels; D001152:Arsenicals; D002118:Calcium; D002413:Cations, Divalent; D004533:Egtazic Acid; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D007457:Iodine Radioisotopes; D015739:Nocodazole; D011509:Proteoglycans; D011990:Receptors, Transferrin; D014357:Trypsin; C029341:oxophenylarsine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid