RT-PCR MICROLOCALIZATION OF MESSENGER-RNAS FOR CALBINDIN-D-28K AND VITAMIN-D-RECEPTOR IN THE MURINE NEPHRON

The spatial relationship between vitamin D receptor (VDR) and calbindi n D-28k [calcium binding protein D-28k (CaBP-D-28k)] gene expression w ithin the murine kidney was studied by localizing their mRNAs in discr ete nephron structures using reverse transcription-polymerase chain re action (RT-PCR). Primers for beta-actin mRNA were used as a control fo r the presence of tissue during RT-PCR for CaBP-D-28k mRNA. mRNA for C aBP-D-28k was found only in distal convoluted tubules (DCTs), connecti ng tubules (CNTs), and cortical collecting ducts (CCDs). In contrast, VDR mRNA was detected in glomeruli, S2 proximal convoluted tubules, co rtical thick ascending limbs of Henle's loop, DCTs, CNTs, and initial CCDs. The presence of both VDR and CaBP-D-28k mRNA in DCTs, CNTs, and CCDs is consistent with the hypothesis that calcitriol acts via the VD R to stimulate CaBP-D-28k synthesis. Conversely, the presence of VDR m RNA in other parts of the nephron suggests that calcitriol has genomic ally mediated actions within the kidney in addition to stimulation of CaBP-D-28k synthesis.