Pathways of phosphate transport in chick jejunum |
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Authors: | Renate Fuchs Meinrad Peterlik |
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Institution: | (1) Institut für allgemeine und experimentelle Pathologie, Universität Wien, Währingerstrasse 13, A-1090 Wien, Austria |
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Abstract: | The effect of vitamin D3 on intestinal phosphate (Pi) absorption was studied in everted sacs prepared from jejunum of either vitamin D-deficient (–D) or vitamin D-replete (+D) chicks. Vitamin D3 stimulates the maximal velocity (V
max) of a mucosal active Pi transport mechanism from 125 to 314 nmol·min–1·g–1 tissue.K
m of this process remains virtually unchanged (–D: 0.15 mmol·l–1; + D: 0.18 mmol·l–1).Active Pi entry into the epithelium depends on extracellular Na+. Reduction of buffer Na+ reducesV
max in the + D group to 182 nmol·min–1·g–1 tissue but has no significant effect in the –D animals (V
max=105 nmol·min–1·g–1 tissue). In this group, the predominant effect of Na+ substitution is a shift ofK
m to 1.13 mmol·l–1, whileK
m in the +D group is changed only to 0.53 mmol·l–1.Transeptithelial Pi transport in the + D group involves the mucosal phosphate pump and hence an intracellular pathway, proceeding at a rate of 48 nmol·min–1·g–1 tissue. This is in contrast to –D Pi transfer (8 nmol·l–1·g–1 tissue) which is by a diffusional, Na+-insensitive, and presumably paracellular pathway.Transepithelial calcium transport (–D: 3.3 nmol·min–1·g–1; + D: 7.6 nmol·min–1·g–1 tissue) does not require the presence of extracellular Na+ and apparently involves pathways different from those of the Pi absorptive system.Presented in part at the Annual Meeting of the Austrian Biochemical Society, Salzburg, September 1978 |
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Keywords: | Phosphate transport Intestine Vitamin D3 Sodium Calcium transport |
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