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Am J Physiol Gastrointest Liver Physiol 255: G482-G489, 1988;
0193-1857/88 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 4 482-G489, Copyright © 1988 by American Physiological Society

ARTICLES

Characterization of calcium transport by basolateral membrane vesicles of human small intestine

K. Kikuchi, T. Kikuchi and F. K. Ghishan
Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.

The present studies investigated the mechanism of Ca2+ transport across basolateral membrane vesicles (BLMVs) prepared from human small intestine. Ca2+ uptake represented transport into the intravesicular space as evident by osmolality study and by the demonstration of Ca2+ efflux from the intravesicular space by Ca2+ ionophore A23187. Ca2+ uptake was stimulated by Mg2+-ATP. Kinetic parameters for ATP-dependent Ca2+ uptake revealed a Michaelis constant (Km) of 0.02 +/- 0.01 microM and a maximum rate of uptake (Vmax) of 1.00 +/- 0.03 nmol.mg protein-1.min-1.Ca2+ uptake in the absence of Mg2+ was inhibited by 75%. The Km of ATP concentration required for half-maximal Ca2+ uptake was 0.50 +/- 0.1 mM. Calmodulin (10 micrograms/ml) increased Vmax to 1.62 +/- 0.02 nmol.mg protein-1.min-1 (P less than 0.001). Km values were 0.017 +/- 0.001 microM, which was not significantly different from control values. Basolateral membranes depleted of calmodulin by EDTA osmotic shock decreased ATP-dependent Ca2+ uptake by 65%. Trifluoperazine, an anticalmodulin drug, inhibited ATP-dependent Ca2+ uptake by 50%, while no inhibition was noted in calmodulin-depleted membranes. Efflux of Ca2+ in the BLMVs was stimulated by trans-Na+. Na+-dependent Ca2+ uptake was saturable with respect to Ca2+ concentration and exhibited a Km of 0.09 +/- 0.03 microM and a Vmax of 1.08 +/- 0.01 nmol.mg protein-1.min-1. These results are consistent with the existence of a Na+-Ca2+ exchange system and ATP and Mg2+-dependent, calmodulin-regulated Ca2+, transport mechanism in BLMVs of human enterocytes.


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J. G. J. Hoenderop, B. Nilius, and R. J. M. Bindels
Calcium Absorption Across Epithelia
Physiol Rev, January 1, 2005; 85(1): 373 - 422.
[Abstract] [Full Text] [PDF]


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