Calcitriol-dependent, paracellular sodium transport in the embryonic chick intestine.
1,25-Dihydroxyvitamin D3 (calcitriol), or vitamin D3 itself, when added to cultures of 20-day-old embryonic chick small intestine, stimulated sodium (Na+) uptake from the mucosal surface. The calcitriol-mediated increase in Na+ uptake appeared to be related to increased tight-junctional or paracellular permeability. Support for this conclusion was, first, that the uptake of other ions, potassium (K+) and rubidium (Rb+), with tight-junctional permeabilities greater than Na+, was also stimulated by calcitriol, and second, perturbation of cellular Na+ and K+ fluxes by inhibition of Na+/K+-ATPase activity did not affect calcitriol-stimulated Na+, K+, or Rb+ transport. Calcitriol stimulation of Na+ fluxes across the brush border as an alternate possibility is unlikely for the following reason: the calcium ionophore A23187, while mimicking the stimulatory action of calcitriol on calcium (Ca2+) uptake, reduced epithelial Na+ uptake. It is therefore suggested that calcitriol, by virtue of its effect on Ca2+ transport, reduces rather than stimulates cellular Na+ uptake.
Cross
H S
HS
Department of General and Experimental Pathology, University of Vienna Medical School, Austria.
Corradino
R A
RA
Peterlik
M
M
D000818:Animals; D001693:Biological Transport, Active; D000001:Calcimycin / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002762:Cholecalciferol / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002762:Cholecalciferol; D000001:Calcimycin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002117:Calcitriol; D002118:Calcium