AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 1 16-G23, Copyright © 1990 by American Physiological Society
Calcium uptake by brush-border and basolateral membrane vesicles in chick duodenum
J. Takito, T. Shinki, T. Sasaki and T. Suda
Department of Biochemistry and Oral Anatomy, School of Dentistry, Showa University, Tokyo, Japan.
Calcium uptake was compared between duodenal brush-border membrane vesicles
(BBMV) and basolateral membrane vesicles (BLMV) isolated from vitamin
D-deficient chicks and those injected with 625 ng of 1
alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. The uptake by BBMV in the
1 alpha,25-(OH)2D3-treated birds attained a maximum (280% of the control)
at 12 h and was maintained at an elevated level (210%) at 24 h after the
injection of the vitamin. In contrast, ATP-dependent calcium uptake by BLMV
reached a maximum (185% of the control) at 6 h and decreased to the control
level at 24 h. The kinetic analysis revealed that 1 alpha,25(OH)2D3
increased Vmax values without any changes in apparent Km values in both
BBMV and BLMV. The activity of ATP-dependent calcium uptake was localized
exclusively in the basolateral membrane, and the activity was inhibited by
vanadate (IC50, 1 microM), but not by oligomycin, theophylline, calmodulin,
trifluoperazine, or calbindin D28K. These results indicate that calcium
transport through both the brush-border and basolateral membranes is
involved in the 1 alpha,25(OH)2D3-dependent intestinal calcium absorption.
The initiation of calcium absorption by 1 alpha,25(OH)2D3 appears to be due
to an increase in the rate of calcium efflux at the basolateral membrane
rather than the rate at the brush-border membrane.
