Expression of genes involved in calcium absorption in human duodenum

Background The role of Vitamin D metabolites in the regulation of expressio n of genes involved in dietary calcium absorption by the human intestine re mains poorly understood despite much work in animals. Materials and methods To investigate this, we measured the expression of tr anscripts for two of these genes, calbindin-D9k and the basolateral membran e calcium pumping ATPase, PMCA1, in duodenal endoscopic biopsies from 40 su bjects. Northern blots were hybridized with previously characterized probes , and the signal was quantified by phosphor imaging. These transcript level s were related to circulating vitamin D metabolites and also analysed accor ding to the vitamin D receptor gene TaqI polymorphism determined in DNA fro m blood. Results Plasma 1,25-dihydroxycholecalciferol correlated significantly with calbindin-D9k RNA (r = 0.4, P < 0.02) but not with PMCA1. Plasma 25-OH-chol ecalciferol was not correlated with transcripts for either gene and, furthe rmore, the mean levels of these transcripts did not differ significantly wh en grouped by vitamin D receptor genotype. Conclusion In normal humans, 1,25-dihydroxycholecalciferol has a small but significant relationship to duodenal expression of calbindin-D9k, but not t o PMCA1 expression.