HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ritter, C. S Articles by Brown, A. J Search for Related Content PubMed PubMed Citation Articles by Ritter, C. S Articles by Brown, A. J

Renal Division, Washington University Medical School, Box 8126, 660 S. Euclid, St Louis, Missouri 63110, USA

((Correspondence should be addressed to A J Brown; Email: brownlab{at}im.wustl.edu) Email: abrown{at}im.wustl.edu)

Extracellular Ca reduces parathyroid hormone (PTH) levels through several mechanisms, but many details of the intracellular steps involved have been difficult to elucidate because of the lack of a suitable parathyroid cell model. The present studies utilized our Ca-responsive bovine parathyroid organoid culture system (pseudoglands) to examine PTH mRNA in intact parathyroid cells. Increasing medium calcium from 0.4 to 3.0 mM reduced PTH mRNA to 20–30% of basal by 16 h. Reducing medium Ca from 3.0 to 0.4 mM restored PTH mRNA levels over a 24-h period. PTH mRNA was also reduced by the calcimimetic R-568, confirming the role of the calcium-sensing receptor. PTH decay rates were determined by placing pseudoglands in either 0.4 or 3.0 mM Ca for 2 h and then blocking gene transcription. PTH mRNA remained stable for at least 24 h in pseudoglands incubated in 0.4 mM Ca, but fell gradually by 62% in the presence of 3.0 mM Ca. Blocking transcription prior to the addition of high-Ca medium dramatically blunted the Ca-induced degradation of PTH mRNA, indicating that acceleration of PTH mRNA decay by Ca requires gene transcription. Pharmacologic investigation of the signaling pathways involved indicated that the Ca-induced reduction of PTH mRNA did not involve MAP kinase, phospholipase D, or cyclic AMP. However, increasing cytosolic Ca with thapsigargin or the Ca ionophore A23187 [GenBank] decreased PTH mRNA levels. In summary, Ca-mediated destabilization of PTH mRNA requires gene transcription and involves increases in cytosolic Ca.