title: Effect of 1,25-dihydroxyvitamin D-3 on phosphate uptake into chick intestinal brush border membrane vesicles.
abstract: Brush border membrane vesicles prepared from the vitamin D-deficient chick duodenum take up phosphate and show an overshoot phenomenon in the presence of NaCl. Substitution of choline chloride for NaCl reduces phosphate uptake. Prior treatment of vitamin D-deficient chicks with 1,25-dihydroxy-vitamin D-3 increases the initial rate of Na+-dependent phosphate uptake into the brush border vesicles. This Na+-dependent phosphate uptake is a saturable process, exhibiting an apparent Km of 0.31 mM and a V of 385 pmol/mg per 15 s. Pretreatment of chicks with 1,25-dihydroxyvitamin D-3 leads to an increase in V (750 pmol/mg per 15 s) without significantly altering the apparent Km (0.33 mM). Addition of Ca2+, either in the presence or absence of the polyene antibiotic, filipin, or of calmodulin, has no effect on Na+-dependent phosphate uptake. Pretreatment of the vitamin D-deficient chick with a dose of cycloheximide sufficient to inhibit membrane protein synthesis blocks the 1,25-dihydroxyvitamin D-3-induced increase in alkaline phosphatase activity, but does not affect the stimulation of Na+-dependent phosphate uptake. From these data, it is concluded that 1,25-dihydroxyvitamin D-3 stimulates Na+-dependent phosphate transport at the brush border membrane of the enterocyte, that alkaline phosphatase is not directly involved in this process, and that this effect of 1,25-dihydroxyvitamin D-3 is independent of new protein synthesis.
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002645:Chickens / Q000378:metabolism; D002762:Cholecalciferol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000201:enzymology / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D013997:Time Factors; D014808:Vitamin D Deficiency / Q000378:metabolism*
chemical_list: D010710:Phosphates; D002762:Cholecalciferol; D000469:Alkaline Phosphatase; D002118:Calcium