Tissue specific expression and differential regulation by 1 alpha,25-dihydroxyvitamin D-3 of the calcium-sensing receptor (CaSR) gene in rat kidney, intestine, and calvaria

The calcium-sensing receptor (CaSR) plays a critical role in calcium (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 analy zed the ontogeny and regulation by 1 alpha ,25-dihydroxyvitamin D-3 (1 alph a ,25(OH)(2)D-3) of CaSR mRNA expression in the kidney, intestine, and bone . In 6-week-old rats, CaSR mRNA was expressed as a major transcript of 8.5 kb and as minor transcripts of 4.8 and 2.5 kb in the kidney, whereas it app eared as faint transcripts of 8.5, 4.0 and 2.5 kb in the intestine and calv aria. These results showed that CaSR mRNAs were expressed in different stru ctures among these organs. Moreover, the level of CaSR mRNA increased in th e kidney from the embryo to the adult. In contrast, the CaSR mRNA level dec reased in the intestine during this transition, and the level of it did not change in the calvaria. Moreover, 1 alpha ,25(OH)(2)D-3 up-regulated the l evel of CaSR mRNA in the kidneys in 6-week-old rats. On the other hand, the 1 alpha ,25(OH)(2)D-3 did not affect the CaSR mRNA expression in the intes tine or calvaria. We concluded that different transcripts of CaSR were expr essed in rat kidney, intestine, and calvaria and that the level of CaSR mRN A was different at various developmental stages in the kidney and intestine . Morever, 1 alpha ,25(OH)(2)D-3 regulated the expression of CaSR mRNA only in the kidney.