Calcium uptake by brush-border and basolateral membrane vesicles in chick duodenum.
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.
Takito
J
J
Department of Biochemistry and Oral Anatomy, School of Dentistry, Showa University, Tokyo, Japan.
Shinki
T
T
Sasaki
T
T
Suda
T
T
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002458:Cell Fractionation; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002645:Chickens; D004386:Duodenum; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008854:Microscopy, Electron; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000378:metabolism
D002132:Calcium Radioisotopes; D009251:NADPH-Ferrihemoprotein Reductase; D000469:Alkaline Phosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D002117:Calcitriol; D002118:Calcium