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.
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.
Mithal
A
A
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
Kifor
O
O
Kifor
I
I
Vassilev
P
P
Butters
R
R
Krapcho
K
K
Simin
R
R
Fuller
F
F
Hebert
S C
SC
Brown
E M
EM
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
D010281:Parathyroid Hormone; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D002118:Calcium