Tissue specific expression and differential regulation by 1α, 25-dihydroxyvitamin D3 of the calcium-sensing receptor (CaSR) gene in rat kidney, intestine, and calvaria

The calcium-sensing receptor (CaSR) plays a critical role incalcium (Ca2+) homeostasis, and it exists in Ca2+ regulatory tissues such as parathyroid, kidney and intestine. As changes in the quality and quantity of CaSR mRNA may have an effect on sensing of extracellular Ca2+ concentration,we analyzed the ontogeny and regulation by 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) of CaSR mRNA expression in the kidney, intestine, and bone. In 6-week-old rats, CaSR mRNA was expressed as a majortranscript of 8.5 kb and as minor transcripts of 4.8 and 2.5 kb in the kidney, whereas it appeared as faint transcripts of 8.5, 4.0 and 2.5 kb in the intestine and calvaria.These results showed that CaSR mRNAs were expressed indifferent structures among these organs. Moreover, the levelof CaSR mRNA increased in the kidney from the embryo to theadult. In contrast, the CaSR mRNA level decreased in theintestine during this transition, and the level of it did notchange in the calvaria. Moreover, 1α,25(OH)2D3 up-regulated the level of CaSR mRNA in thekidneys in 6-week-old rats. On the other hand, the 1α,25(OH)2D3 did not affect the CaSR mRNA expression in the intestine or calvaria. We concluded that different transcripts of CaSR were expressed in rat kidney, intestine, and calvaria and that the level of CaSR mRNA was different atvarious developmental stages in the kidney and intestine. Morever, 1α,25(OH)2D3 regulated the expression of CaSR mRNA only in the kidney.