1,25-Dihydroxycholecalciferol-related Na+/D-glucose transport in brush-border membrane vesicles from embryonic chick jejunum. Modulation by triiodothyronine.
1,25-Dihydroxycholecalciferol, when present at and above 10 nM in an organ-culture system of embryonic chick jejunum, approximately doubled the rate of Na(+)-gradient-driven D-glucose uptake by brush-border membrane vesicles, but had no effect on Na(+)-independent D-glucose transfer. The sterol also had no effect on Na+ influx along an outside/inside Na+ gradient ([Na+]o = 100 mM; [Na+]i = 0 mM). This renders it unlikely that in embryonic intestine, calcitriol raises Na(+)-dependent D-glucose transport through changes in the electrochemical Na+ gradient. D-[U-14C]Glucose tracer exchange, measured under voltage-clamp condition at Na+/D-glucose equilibrium, revealed that addition of calcitriol to the culture medium approximately doubled the activity of the Na+/D-glucose transporter in the brush-border membrane. This was also reflected by an corresponding increase in the maximal velocity of the transfer process. Increased [3H]phlorizin binding after calcitriol treatment suggests that the steroid hormone activates Na+/D-glucose transport through increasing the number of carrier molecules in the brush-border membrane. 10 nM triiodothyronine, which by itself has no effect on Na(+)-dependent D-glucose transport, potentiated the effect of 1,25-dihydroxycholecalciferol such that in the presence of both hormones, Na+/D-glucose-carrier activity was increased fourfold above control levels.
Department of Biochemistry and Experimental Medicine, Child's Health Center, Warsaw, Poland.
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Peterlik
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D002642:Chick Embryo; D004357:Drug Synergism; D005947:Glucose / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000196:embryology / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000187:drug effects; D009924:Organ Culture Techniques; D010695:Phlorhizin / Q000378:metabolism; D011869:Radioligand Assay; D012964:Sodium / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology*
D009004:Monosaccharide Transport Proteins; D014284:Triiodothyronine; D012964:Sodium; D010695:Phlorhizin; D002117:Calcitriol; D005947:Glucose