title: Calcium binding activity by chick intestinal brush-border membrane vesicles.
abstract: Uptake of Ca2+ by vesicle preparation of chick intestinal brush-border membranes was rapid and extensive. With tracer quantities of Ca2+ uptake was complete in 10 min whereas with 2.0 mM Ca2+ maximum uptake by the vesicles occurred after one hour incubation. The maximum concentration of Ca2+ found in the vesicles was four times greater than the external Ca2+ concentration showing that the majority of the Ca2+ was membrane bound. The Ca2+ taken up by the vesicles was probably bound to the vesicle's interior since it was not replaced by exposure of loaded vesicles to La3+ (5 mM). The uptake of Ca2+ by the vesicles at different Ca2+ concentrations was analyzed and a high affinity Ca2+ binding site was found with an association constant for Ca2+ of 5 x 10(-5) M. More of the sites were found in the duodenum than the ileum and vitamin D increases the number of these sites.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002645:Chickens / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism*; D014807:Vitamin D / Q000494:pharmacology
chemical_list: D014807:Vitamin D; D002118:Calcium