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Pflügers Archiv

, Volume 381, Issue 3, pp 217–222 | Cite as

Pathways of phosphate transport in chick jejunum

Influence of vitamin D and extracellular sodium
  • Renate Fuchs
  • Meinrad Peterlik
Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands

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 (Vmax) of a mucosal active Pi transport mechanism from 125 to 314 nmol·min−1·g−1 tissue.Km 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+ reducesVmax in the + D group to 182 nmol·min−1·g−1 tissue but has no significant effect in the −D animals (Vmax=105 nmol·min−1·g−1 tissue). In this group, the predominant effect of Na+ substitution is a shift ofKm to 1.13 mmol·l−1, whileKm 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.

Key words

Phosphate transport Intestine Vitamin D3 Sodium Calcium transport 

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Copyright information

© Springer-Verlag 1979

Authors and Affiliations

  • Renate Fuchs
    • 1
  • Meinrad Peterlik
    • 1
  1. 1.Institut für allgemeine und experimentelle PathologieUniversität WienWienAustria

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