Journal
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
Volume 283, Issue 3, Pages G618-G625Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpgi.00269.2001
Keywords
intestine; calcium absorption; calbindin D-9k; calcium transport channel; plasma membrane Ca-adenosinetriphosphatase
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Funding
- NIDDK NIH HHS [R01 DK054111, R01 DK054111-03, DK-54111] Funding Source: Medline
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The parental cell line (P) of Caco-2 cells and two clones, BBe and TC7, were studied at 11 days postconfluence to test the facilitated diffusion model of vitamin D-mediated intestinal calcium absorption (CaTx). Nuclear vitamin D receptor (nVDR) and calbindin D-9k (CaBP) were measured by Western blot; 1,25-hydroxyvitamin D-3 24-hydroxylase (CYP24), CaBP, plasma membrane Ca-ATPase (PMCA), and Ca transport channel (CaT1) mRNA levels were examined by RTPCR; and net apical-to-basolateral CaTx was examined after treating cells with vehicle or 10 nM calcitriol for 8 (mRNA levels) or 48 h (protein, CaBP mRNA, CaTx). nVDR level was lowest in BBe (38% P value) and directly related to CYP24 induction (TC7 = P, which were 1.56 times greater than BBe). nVDR was inversely related to the vitamin D-induced levels of CaT1 mRNA, CaBP mRNA, PMCA mRNA, and net CaTx, with the highest induction seen in BBe. Basal CaBP mRNA (86 times greater than P) and protein levels were highest in TC7 cells and were not associated with higher net CaTx, suggesting CaBP may not be rate limiting for CaTx in these cells.
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