title: Calcium accumulation by chick intestinal mitochondria. Regulation by vitamin D-3 and 1,25-dihydroxyvitamin D-3.
abstract: We have the evaluated the effect of vitamin D-3 and its metabolite 1,25-dihydroxyvitamin D-3 on Ca2+ accumulation by chick intestinal mitochondria. Ca2+ accumulation appears to occur in two phases: an early, transient accumulation into an Na+-labile pool followed by an ATP-dependent accumulation into an Na+-resistant pool. Ca2+ accumulation is extensive at free Ca2+ concentrations greater than 3 . 10(-6) M in the presence of ATP. Ruthenium red and dinitrophenol block Ca2+ accumulation, but atractyloside does not. Oligomycin blocks ATP-supported accumulation completely with a partial inhibition of ATP and malate-supported accumulation. Little difference could be found in mitochondrial preparations from vitamin D-deficient chicks compared to those from vitamin D-3 (or 1,25(OH)2D-3)-supplemented chicks with respect to respiratory control, oxygen consumption, efficiency of oxidative phosphorylation, affinity for Ca2+, or the rate and extent of ATP-supported Ca2+ accumulation. Intestinal cytosol stimulated Ca2+ accumulation, but this was not specific  with respect to vitamin D status or tissue of origin, nor was it duplicated by chick intestinal Ca2+-binding protein. 30 ng/ml 1,25(OH)2D-3 stimulated Ca2+ accumulation directly, regardless of the presence of intestinal cytosol. Other vitamin D metabolites were less potent: 25-hydroxyvitamin D-3 greater than 24,25-dihydroxyvitamin D-3 = vitamin D-3. Since increasing the free Ca2+ concentration from 3 . 10(-6) to 1 . 10(-5) M increased Ca2+ accumulation approx. 50-fold, whereas direct stimulation by 1,25(OH)2D-3 in vitro increased Ca2+ accumulation less than 2-fold, we conclude that 1,25(OH)2D-3 influences mitochondrial accumulation of Ca2+ in vivo primarily by altering cytosol concentrations of free Ca2+.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001278:Atractyloside / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002117:Calcitriol; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D002762:Cholecalciferol / Q000494:pharmacology*; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D004140:Dinitrophenols / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism*; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D012430:Ruthenium Red / Q000494:pharmacology
chemical_list: D004100:Dihydroxycholecalciferols; D004140:Dinitrophenols; D006887:Hydroxycholecalciferols; D009840:Oligomycins; D012430:Ruthenium Red; D001278:Atractyloside; D002762:Cholecalciferol; D000255:Adenosine Triphosphate; D002117:Calcitriol; D002118:Calcium