1,25-Dihydroxyvitamin D3 Stimulates Calcium and Phosphate Absorption by Different Mechanisms: Contrasting Requirements for Sodium
Previous studies from our laboratory have demonstrated that 1,25-dihydroxyvitamin D3 (1,25D) stimulates separate calcium (Ca) and inorganic phosphate (P) absorptive mechanisms in rat intestine (1,2). The proportion of Ca to P “pumps” varies in different regions of the intestine. Thus, there is a preponderance of Ca pumps in the duodenum, a preponderance of P pumps in the jejunum and an equal distribution of Ca and P pumps in the ileum (3). Interestingly, the colon has only 1,25D-responsive Ca pumps (2). The active Ca absorptive mechanisms in duodenum, ileum and colon appear to share certain characteristics, all exhibiting a Km of approximately 1 mM (2,3). The expression of this 1,25D-induced Ca absorption in colon does not appear to require the presence of extracellular sodium ions (4). In the present study we examined the sodium (Na) requirement of 1,25D-stimulated P transport processes in rat jejunum.
KeywordsBrush Border Membrane Phosphate Transport Rabbit Small Intestine Absorptive Mechanism Unidirectional Influx
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- 3.Walling MW and Lee DBN: Theories on the mechanism of action of 1,25(OH)2D3 on active intestinal calcium and inorganic phosphate absorption: are the calcium and phosphate transport processes coupled, uncoupled or both? In: Norman AW, Schaefer K, Herrath DV, Grigoleit HG, Coburn JW, DeLuca HF, Mawer EB and Suda T (Eds), “Vitamin D: Basic Research and Its Clinical Applications”, Walter de Gruyter, Berlin/New York, 1979, pp 687–692.Google Scholar