*P<0

*P<0.05, n.s. below the assay detection limit; in TE-85 TRPV6 mRNA was detected at 6.901.9 105relative to B2M. In contrast, TRPV6 was detected at 7.73.0 102and 2.380.28 104the level of B2M in human carcinoma-derived cell lines LNCaP and CaCO-2 respectively. In murine primary calvarial osteoblasts TRPV6 was detected at 3.800.24 105relative to GAPDH, in contrast with 4.31.5 102relative to GAPDH in murine duodenum. By immunohistochemistry, TRPV6 was expressed mainly in myleocytic cells of the murine bone marrow and was observed only at low levels in murine osteoblasts, osteocytes or growth plate cartilage. == Conclusions == TRPV6 is usually expressed only at low levels in osteoblasts and plays little functional role in osteoblastic calcium uptake. == Introduction == Skeletal mineral includes a dynamic store of calcium ions that can be accessed rapidly in the absence of dietary sources to maintain the plasma concentration within tightly regulated limits. Calcium homeostasis involves both active and passive absorptive mechanisms in the intestine, both constitutive and regulated reabsorptive processes in the kidney and the exchange between mineralized and ionized forms of calcium in bones[1],[2]. Two of the key molecules that mediate intestinal absorption and renal reabsorption of Ca2+have recently been identified. TRPV6, a Ca2+selective member of the transient receptor potential vanilloid class of ion channels, was detected in epithelial cells of the small intestine and was described as the gatekeeper of active Ca2+absorption from the DKFZp686G052 diet[3],[4],[5],[6]. TRPV5, a closely related homologue, was identified as the principal mediator of regulated Ca2+reabsorption in the distal convoluted tubules of the kidney[7]. Ca2+is usually transferred from the intestinal or the renal tubular lumen into epithelial cells via these key ion channels which are expressed around PF299804 (Dacomitinib, PF299) the apical cell surface, transported through the cell complexed with the Ca2+binding proteins calbindinD9Kand D28K, and is extruded through the basolateral membrane via the Ca2+exchangers NCX1 and PMCA1b[8],[9],[10]. Mice in whichTrpv6is usually ablated globally (Trpv6-/-) were reported to exhibit 60% lower intestinal Ca2+absorption, secondary hyperparathyroidism, a greater than 2-fold higher Ca2+excretion and 9.3% reduce femoral bone mineral density (BMD) compared with wild type (WT) littermates[11]. The low BMD in these mice is usually consistent with the proposed role of TRPV6 in intestinal and renal absorption of Ca2+as a consequence of reduced Ca2+availability for mineralization. However, in their study, Biancoet al.[11]were unable to rescue the BMD ofTrpv6-/-mice with a high (2%) Ca2+diet and the relative PF299804 (Dacomitinib, PF299) increase in BMD inTrpv6-/-mice on this diet was lower than in wild-type littermates[11]. On a low Ca2+diet,Trpv6-/-mice did not increase their urinary deoxypirodinoline excretion. The authors argued these findings showed PF299804 (Dacomitinib, PF299) that this bones and kidneys ofTrpv6-/-mice do not respond to parathyroid hormone (PTH) and 1,25-dihydroxy vitamin D3 (1,25D3), implying a role for TRPV6 in both tissues. A number of previous studies report that osteoblasts express all the key molecular components of the transepithelial calcium transport pathway. Balmainet al.[12]provided the first immunohistological evidence that calbindinD9Kis expressed by both osteoblasts and osteocytes and that its synthesis in trabecular bone is usually regulated by 1,25D3. Berdalet al.[13]showed that both calbindinD9Kand D28Kare expressed in rat osteoblasts, while Faucheuxet al.[14]demonstrated the production of calbindin-D28Kduring mineralization in human bone marrow stromal cells. Lundquistet al.[15]demonstrated the expression of three isoforms of the NCX1 Na+/Ca2+exchanger in primary rat odontoblasts and osteoblasts and in a rat and a human osteoblastic cell line. Meszaros and Karin[16]showed that primary rat osteoblasts and osteoblast-like osteosarcoma cells express PMCA1b, an isoform of the plasma membrane calcium ATPase. Weberet al.[17]demonstrated that ECaC2 (TRPV6) and calbindin-D9K, but not ECaC1 (TRPV5) or calbindin-D28K, were strongly expressed in primary murine calvarial osteoblasts and whole bones. Nijenhuiset al.[18]also detected mRNA for TRPV6 in whole murine bone. Taken together, the evidence suggested that a complete mechanism existed for the involvement of TRPV6 in osteoblastic calcium handling, and led us to hypothesize that.