NDT Advance Access published online on June 13, 2008
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfn338
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Simultaneous changes in the calcium-sensing receptor and the vitamin D receptor under the influence of calcium and calcitriol
1 Bone and Mineral Research Unit, Instituto Reina Sofía de Investigación, Hospital Universitario Central de Asturias, REDinREN del ISCIII, Universidad de Oviedo, Oviedo, Asturias 2 Experimental Nephrology Laboratory, Hospital Universitario Arnau de Vilanova, IRBLLEIDA, REDinREN del ISCIII, Lleida, Spain
Correspondence and offprint requests to: Jorge B. Cannata-Andía, Bone and Mineral Research Unit, Instituto Reina Sofía de Investigación, Hospital Universitario Central de Asturias, C/Julián Clavería s/n, 33006 Oviedo, Asturias, Spain. Tel: +34-985106137; Fax: +34-985106142; E-mail: metoseo{at}hca.es
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Abstract |
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Background. The regulatory mechanisms of parathyroid hormone (PTH) synthesis are complex, involving calcium, calcitriol, the calcium-sensing receptor (CaR) and the vitamin D receptor (VDR). In this study, the effects of calcium and calcitriol on the simultaneous expression of CaR and VDR mRNA and protein levels were assessed in parathyroid glands cultured in vitro.
Methods. Parathyroid glands (N = 424) were removed and cultured for 24 h to study the effect of calcium on the CaR, VDR and PTH. In addition, the effect of calcitriol at low calcium concentrations (0.6 mM) on CaR and VDR levels was studied after 48 h of incubation. CaR, VDR and PTH mRNAs were measured by quantitative real-time PCR (qRT-PCR), and CaR and VDR protein levels were measured by immunohistochemistry.
Results. PTH gene expression was reduced by high calcium concentration. No differences were found in the CaR mRNA levels among the different calcium concentrations tested (0.6 mM calcium: 100%; 1.2 mM calcium: 120%; 2.0 mM calcium: 112%; median values), but VDR gene expression rose when calcium increased (0.6 mM calcium: 100%; 1.2 mM calcium: 164%; 2.0 mM calcium: 195%; median values). Calcitriol increased both CaR (control: 100%; 10–8 M calcitriol: 196%; median values) and VDR genes expression (control: 100%; 10–8 M calcitriol: 176%; median values). The same findings were corroborated at protein levels for both CaR and VDR.
Conclusions. In parathyroid glands cultured in vitro, calcium up-regulates VDR but not CaR. Conversely, calcitriol up-regulates both VDR and CaR mRNAs and protein levels, even at low calcium concentrations.
Keywords: calcitriol; calcium; CaR; VDR
Received for publication: 5. 2.08
Accepted in revised form: 22. 5.08
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