title: The reduced responsiveness of cultured bovine parathyroid cells to extracellular Ca2+ is associated with marked reduction in the expression of extracellular Ca(2+)-sensing receptor messenger ribonucleic acid and protein.
abstract: PTH secretion from dispersed bovine parathyroid cells maintained in culture becomes progressively less responsive to changes in the extracellular Ca2+ concentration (Ca2+o) over several days. We have now investigated whether this change in secretory control is associated with alterations in the expression of the Ca2+o-sensing receptor (BoPCaR) recently cloned from bovine parathyroid, which plays a central role in Ca2+o-regulated PTH secretion. BoPCaR messenger RNA levels dropped rapidly in cultured bovine parathyroid cells, as assessed by Northern analysis, decreasing by 78% within 18 h and remaining low for at least 4 days. The level of receptor protein decreased to a comparable extent (approximately 72-82%) after 3-4 days in culture, as determined by immunocytochemistry with specific antibodies directed at the extracellular domain of the receptor. The half-time for the reduction in receptor protein (approximately 2 days) was considerably longer, however, than that for BoPCaR messenger RNA, but was comparable to that for the loss of sensitivity of PTH secretion to Ca2+o. Indeed, there was a close linear correlation between maximal suppressibility of PTH secretion and the intensity of staining for the receptor protein (r = 0.88; P = 0.004). We conclude that alterations in the expression of BoPCaR could explain much of the reduced responsiveness of cultured bovine parathyroid cells to Ca2+o.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: A
authors.initials: A
authors.lastname: Mithal
authors.forename: O
authors.initials: O
authors.lastname: Kifor
authors.forename: I
authors.initials: I
authors.lastname: Kifor
authors.forename: P
authors.initials: P
authors.lastname: Vassilev
authors.forename: R
authors.initials: R
authors.lastname: Butters
authors.forename: K
authors.initials: K
authors.lastname: Krapcho
authors.forename: R
authors.initials: R
authors.lastname: Simin
authors.forename: F
authors.initials: F
authors.lastname: Fuller
authors.forename: S C
authors.initials: SC
authors.lastname: Hebert
authors.forename: E M
authors.initials: EM
authors.lastname: Brown
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002478:Cells, Cultured; D015870:Gene Expression; D007124:Immunoenzyme Techniques; D010280:Parathyroid Glands / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism
chemical_list: D010281:Parathyroid Hormone; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D002118:Calcium