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Am J Physiol Gastrointest Liver Physiol 256: G124-G128, 1989;
0193-1857/89 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 1 124-G128, Copyright © 1989 by American Physiological Society

ARTICLES

Calbindin-D9k stimulates the calcium pump in rat enterocyte basolateral membranes

J. R. Walters
Department of Medicine, State University of New York, Buffalo General Hospital 14203.

Calbindin-D9k, a vitamin D-dependent Ca2+-binding protein, is closely associated with the transcellular absorption of calcium by mammalian enterocytes. Studies were performed to determine whether physiological concentrations of calbindin-D9k altered Ca2+ transport by the ATP-dependent Ca2+ pump in rat duodenal basolateral membrane vesicles. In solutions where free Ca2+ was buffered by EGTA, only a small stimulation of Ca2+ uptake rates could be demonstrated, and it was likely that this was secondary to changes in free Ca2+ concentration. However, a threefold stimulation of uptake by 30 microM calbindin-D9k was found when EGTA-free solutions were used, and changes in free Ca2+ activity or 45Ca2+ specific activity were avoided. The affinity for Ca2+ was reduced in this system but appeared to be stimulated by either calbindin-D9k or EGTA. Other Ca2+-binding proteins that bind Ca2+ in the micromolar range were found to increase Ca2+ uptake in the absence of EGTA. These experiments suggest that one of the actions of calbindin-D9k is to stimulate the rate of extrusion of Ca2+ from the enterocyte by increasing Ca2+ transport by the Ca2+ pump.


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H. J. Armbrecht, M. A. Boltz, and V. B. Kumar
Intestinal plasma membrane calcium pump protein and its induction by 1,25(OH)2D3 decrease with age
Am J Physiol Gastrointest Liver Physiol, July 1, 1999; 277(1): G41 - G47.
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