Localization of vitamin D-dependent active Ca2+ transport in rat duodenum and relation to CaBP.
Vitamin D-replete (+D) and vitamin D-deficient (-D) rats received by intraperitoneal injection varying amounts of 1,25-dihydroxyvitamin D3, and 4 h (+D) or 9 h (-D) later everted duodenal sacs were prepared to evaluate active calcium transport, i.e., the amount of calcium found in the serosal fluid. At the same time, duodenal calcium-binding protein (CaBP) content was measured. Calcium transport was a close positive function of CaBP content. It was not detectable when CaBP content was zero and increased linearly without plateauing as CaBP content increased to 100 nmol calcium bound/g mucosa. Trifluoperazine (TFP) inhibited active calcium transport in a concentration-dependent manner. Experiments using vesicles prepared from brush-border or basolateral membranes indicated that TFP inhibited the calcium-extrusion process, with virtually no effect on calcium entry. It is concluded that vitamin D exerts its major regulation of active calcium transport in the rat duodenum via CaBP on transport steps beyond brush-border entry.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology; D014808:Vitamin D Deficiency / Q000378:metabolism
D002135:Calcium-Binding Proteins; D064030:S100 Calcium Binding Protein G; D014268:Trifluoperazine; D002117:Calcitriol; D002118:Calcium