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Free access | 10.1172/JCI109796

Calcium and Inorganic Phosphate Transport in Rat Colon: DISSOCIATED RESPONSE TO 1,25-DIHYDROXYVITAMIN D3

D. B. N. Lee, M. W. Walling, U. Gafter, V. Silis, and J. W. Coburn

Medical and Research Services, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073

Department of Medicine, University of California, Los Angeles, California 90073

School of Medicine, University of California, Los Angeles, California 90073

Department of Orthodontics, University of California, Los Angeles, California 90073

School of Dentistry, Los Angeles, California 90073

†

Deceased, 30 November 1979.

Find articles by Lee, D. in: PubMed | Google Scholar

Medical and Research Services, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073

Department of Medicine, University of California, Los Angeles, California 90073

School of Medicine, University of California, Los Angeles, California 90073

Department of Orthodontics, University of California, Los Angeles, California 90073

School of Dentistry, Los Angeles, California 90073

†

Deceased, 30 November 1979.

Find articles by Walling, M. in: PubMed | Google Scholar

Medical and Research Services, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073

Department of Medicine, University of California, Los Angeles, California 90073

School of Medicine, University of California, Los Angeles, California 90073

Department of Orthodontics, University of California, Los Angeles, California 90073

School of Dentistry, Los Angeles, California 90073

†

Deceased, 30 November 1979.

Find articles by Gafter, U. in: PubMed | Google Scholar

Medical and Research Services, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073

Department of Medicine, University of California, Los Angeles, California 90073

School of Medicine, University of California, Los Angeles, California 90073

Department of Orthodontics, University of California, Los Angeles, California 90073

School of Dentistry, Los Angeles, California 90073

†

Deceased, 30 November 1979.

Find articles by Silis, V. in: PubMed | Google Scholar

Medical and Research Services, Veterans Administration Wadsworth Medical Center, Los Angeles, California 90073

Department of Medicine, University of California, Los Angeles, California 90073

School of Medicine, University of California, Los Angeles, California 90073

Department of Orthodontics, University of California, Los Angeles, California 90073

School of Dentistry, Los Angeles, California 90073

†

Deceased, 30 November 1979.

Find articles by Coburn, J. in: PubMed | Google Scholar

Published June 1, 1980 - More info

Published in Volume 65, Issue 6 on June 1, 1980
J Clin Invest. 1980;65(6):1326–1331. https://doi.org/10.1172/JCI109796.
© 1980 The American Society for Clinical Investigation
Published June 1, 1980 - Version history
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Abstract

In the small intestine, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] stimulates both calcium (Ca) and inorganic phosphate (Pi) absorption. This is mediated through an increase in mucosal-to-serosal flux (Jms) whereas the serosal-to-mucosal flux (Jsm) remains unchanged. We now report that in rat proximal colon, 1,25(OH)2D3 produces active Ca absorption without affecting Pi transport, and that this induced active Ca absorption is associated with alterations in kinetics of both Jms and Jsm so that both processes demonstrate saturable components. Vitamin D-deficient rats were given daily injections of solvent (−D) or 270 ng 1,25(OH)2D3 (+D) for 3 d. 45Ca and [32P]phosphate fluxes were measured employing the Ussing technique using a modified Krebs-Ringer-HCO3 buffer ([Ca] 1.25, [Pi] 1.18, [glucose] 11 mM). In −D rats there was no net flux (Jnet) of either Ca or Pi. In +D rats net active Ca absorption was observed (−D = 3.3 nmol/cm2 per h ±3.4 (SEM); +D = 27.3 ±3.8, n = 11, P < 0.001) whereas Pi transport was unchanged, i.e., still no Jnet. Pi Jms was not different from Pi Jsm measured at the following buffer [Pi]: 0.0118, 0.118, 1.18, and 2.36 mM. Ca saturation kinetics were estimated using buffer [Ca] from 0.0125 to 5.0 mM. Saturable processes were demonstrated for both Jms and Jsm. Jnet for Ca across colon from +D rats exhibited saturation at [Ca] > 3 mM, with an estimated Vmax of 44.0 nmol/cm2 per h and a Km of 0.9 mM. This colonic model may provide a useful system for studying 1,25(OH)2D3-induced molecular events related to Ca but not Pi transport. The apparent action of 1,25(OH)2D3 on Ca secretory process may furnish new insights into the mechanism of action of vitamin D.

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