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https://doi.org/10.1016/0005-2736(92)90082-w
Copy DOIJournal: BBA - Biomembranes | Publication Date: Aug 24, 1992 |
Citations: 26 |
BBMV were prepared from duodenal segments of untreated, 1,25-(OH) 2D 3- or vitamin D-3-treated rachitic piglets and from non-rachitic controls by the Mg 2+ precipitation method. The rachitic piglets were offspring from the ‘Hannover Pig Strain’ which suffer from pseudo vitamin D-deficiency rickets, type I (no renal 1-hydroxylase activity). Initial uptake of Ca 2+ (up to 35 s) at low [Ca 2+] (between 0.02–0.25 mmol/l) into isolated BBMV consisted of a saturable and non-saturable component. The apparent V max of the saturable component was significantly lower in rachitic piglets than in control piglets. In the presence of an inside negative potassium diffusion potential, the difference in uptake extended over at least 15 min. The apparent K m of Ca 2+-uptake was not influenced by the rachitic condition. Treatment of rachitic piglets with sequential doses of 1,25-(OH) 2D 3 for three days 91 μg/day) or with a single dose (2.5 mg) of vitamin D-3 elevated the saturable Ca 2+-uptake component to values similar to those of control piglets. Addition of 1 mmol/l verapamil to the vesicular suspension inhibited Ca 2+-uptake in BBMV of control piglets by 40–60% but was without effect on preparations from rachitic piglets. It was concluded from the study that 1,25-(OH) 2D 3 dependent Ca 2+-uptake unto BBMV constituted a saturable process which can be inhibited by a known Ca 2+-channel blocking agent. It appears that 1,25-(OH) 2D 3 increases the number of verapamil sensitive Ca 2+-transport components in brush-border membranes. The vitamin D-dependent changes in vesicular Ca 2+-uptake were paralleled by the expression of an active transmural Ca 2+-transport across the mucosa.
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