ISSN:
1432-1424
Schlagwort(e):
vitamin D-dependent calcium uptake
;
intestinal cell calcium transport
;
intestinal brush-border calcium uptake
;
vitamin D-deficient chicks
;
vitamin D, mechanism of action
;
1,25-dihydroxycholecalciferol
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Summary Thein vivo andin vitro effects of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on calcium uptake by isolated chick duodenal cells were studied.In vivo, 1,25-(OH)2D3 given orally to vitamin D-deficient chicks increased the initial rate of calcium uptake by cells prepared 1 hr after administration of the hormone. The rate was stimulated approximately 100%, 17 to 24 hr after repletion.In vitro, pre-incubation of 1,25-(OH)2D3 with cells from D-deficient chicks increased the cellular rate of calcium uptake in a concentration-dependent relationship. Enhancement was found with 10−15 m, was maximal at 10−13 m, and was diminished at higher (10−11 m) concentrations. Stimulation was observed after a pre-incubation period as brief as 1 hr. The potency order for vitamin D3 analogs was 1,25-(OH)2D3=1-(OH)D3〉25-(OH)D3〉1,24,25-(OH)3D3〉24,25-(OH)2D3〉D3. The maximal enhancement in calcium uptake induced by the analogs was the same, only the concentration at which the cell responded was different. The effectiveness of 1,25-(OH)2D3 was five orders of magnitude greater than D3. Kinetically, 1,25-(OH)2D3 increased theV max of calcium uptake; the affinity for calcium (K m=0.54mm) was unchanged. The enhanced uptake found after the cells were pre-incubated for 2 hr with the hormone was completely blocked by inhibitors of protein synthesis. 1,25-(OH)2D3,in vitro, also increased calcium uptake in cells isolated from D-replete chicks. The maximal rates of uptake were the same in cells from D-deficient and D-replete animals. The hormone had no effect of calcium efflux from cells. Calcium uptake in microvillar brush-border membrane vesicles was increased by 1,25-(OH)2D3. These findings suggest that thein vitro cell system described in this paper represents an appropriate model to examine the temporal relationships between 1,25-(OH)2D3 induction of calcium transport and specific biochemical correlates.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01869932
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