Calcium uptake by brush-border and basolateral membrane vesicles in chick duodenum

• Published in: The American journal of physiology Vol. 258; no. 1 Pt 1; p. G16
• Main Authors: Takito, J, Shinki, T, Sasaki, T, Suda, T
• Format: Journal Article
• Language: English
• Published: United States 01.01.1990
• Subjects: Alkaline Phosphatase - metabolism; Animals; Biological Transport, Active - drug effects; Calcitriol - pharmacology; Calcium - metabolism; Calcium Radioisotopes; Cell Fractionation; Cell Membrane - drug effects; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Chickens; Duodenum; Intestinal Absorption - drug effects; Intestinal Mucosa - drug effects; Intestinal Mucosa - metabolism; Kinetics; Male; Microscopy, Electron; Microvilli - drug effects; Microvilli - metabolism; Microvilli - ultrastructure; NADPH-Ferrihemoprotein Reductase - metabolism; Sodium-Potassium-Exchanging ATPase - metabolism; Vitamin D Deficiency - metabolism
• ISSN: 0002-9513; 2163-5773
• DOI: 10.1152/ajpgi.1990.258.1.G16

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.