1,25-Dihydroxyvitamin D Up Regulates The Expression Of CaT1 mRNA In Caco-2 Cells. Cells were treated with ethanol vehicle or 1,25-dihydroxyvitamin D (100 nM, 10 -7 mol/L) for 24 h. Total RNA was harvested and CaT1 mRNA (28 cycles) and GAPDH mRNA (21 cycles) were determined by RT-PCR. The PCR products were electrophoresed on a 2% agarose gel and stained with ethidium bromide for visualization and digital capture. The upper picture in the illustration shows the CaT1 PCR products from 6 individual wells of a single experiment (3 control and 3 + 1,25-dihydroxyvitamin D). CaT1 expression in the gel has been juxtaposed on top of the corresponding GAPDH expression. GAPDH is a housekeeping gene used to standardize CaT1 mRNA expression. Low levels of CaT1 mRNA are discernable in the absence of vitamin D treatment and the up regulating effect of 1,25-dihydroxyvitamin D by 24 h of treatment is clearly evident. The bar graph shows the combined mean (SEM) effect of 1,25-dihydroxyvitamin D on CaT1 expression normalized for GAPDH from 10 independent studies. 1,25-dihydroxyvitamin D treatment caused a significant (p < 0.001) 10-fold increase in CaT1 mRNA expression compared to vehicle treated control cells.