Characterization of the Human Intestinal Calcium Transporter, CaT1, Stably Expressed in CHO Cells

The human calcium transporter, hCaT1, was cloned and analyzed. The obtained amino acid sequence was slightly different from the ortholog of hCaT1 which had been identified by Peng et al. (2000. Biochem. Biophys. Res. Commun 278: 326-332). An mRNA analysis of human gastrointestinal segments demonstrates that hCaT1 was expressed in the stomach, duodenum, jejunum, ileum, ileocecum, cecum, ascending colon, transverse colon, descending colon, and, at very low levels, in the esophagus and rectum. hCaT1 was transiently expressed by transfecting COS-1 cells and was stably expressed by the transfected CHO cells. The transfected cells expressed hCaT1 with a molecular mass of 75 kDa. Stable expression of hCaT1 in the CHO cells increased the cellular uptake of Ca(2+). hCaT1 was inhibited by La(3+), Gd(3+) and Cd(2+), whereas Co(2+), Fe(2+), Mn(2+) and Mg(2+) showed no significant effects on the activity. Acidification of the extracellular solution to pH 5.5 reduced the (45)Ca(2+)uptake by hCaT1 in the CHO cells. The addition of lactose and raffinose had no effect on the (45)Ca(2+) uptake, whereas galactose and glucose increased the (45)Ca(2+) uptake. CHO cells stably expressing hCaT1 will be useful to detect and analyze food substances that could modulate the hCaT1 activity.