AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 3 613-G617, Copyright © 1989 by American Physiological Society
Effects of 1,25(OH)2D3 on enterocyte basolateral membrane Ca transport in rats
M. J. Favus, V. Tembe, K. A. Ambrosic and H. N. Nellans
Department of Medicine, University of Chicago Pritzker School of Medicine 60637.
One, twenty-five dihydroxyvitamin D3 [1,25(OH)2D3], commonly known as
calcitriol, stimulates intestinal Ca absorption through increased activity
of a cellular transport process. To determine whether transcellular Ca
transport involves energy-dependent Ca efflux across enterocyte plasma
membrane in vitamin D-sufficient rats, in vitro bidirectional Ca fluxes
were measured under short-circuited conditions across proximal duodenum
from rats fed diets adequate in vitamin D and containing a normal Ca diet
(NCD), a low Ca diet (LCD), or fed NCD and injected with 50 ng of
1,25(OH)2D3 daily for 4 days before study. LCD or 1,25(OH)2D3 increased Ca
net flux [Jnet, mucosal-to-serosal flux minus the serosal-to-mucosal flux]
by increasing Ca mucosal-to-serosal flux (Jm----s) (mean +/- SE, NCD vs.
LCD vs. 1,25(OH)2D3, 16 +/- 4 vs. 179 +/- 18 vs. 82 +/- 21 nmol.cm-2. h-1,
P less than 0.0001). Initial ATP-dependent Ca uptake rates by duodenal
basolateral membrane vesicles (BLMV) was greater in vesicles from rats fed
NCD compared with LCD and not different from NCD injected with 1,25(OH)2D3.
These studies suggest that in vitamin D-replete animals, 1,25(OH)2D3
increases epithelial Ca Jm----s by mechanisms that do not involve
ATP-dependent BLM Ca efflux. ATP-dependent Ca exit from the cell under
these conditions may play a role in intracellular Ca homeostasis rather
than Ca absorption.
