Role of transcellular pathway in ileal Ca2+ absorption: stimulation by low-Ca2+ diet.
The present study was performed to determine the respective involvement of the cellular and paracellular routes in ileal Ca2+ transport. Two groups of rats were either fed a normal Ca2+ diet (1. 0%) or a Ca2+-deficient diet (0.02%) for 14 days. Ileal Ca2+ absorption was determined using both an in situ method of continuous luminal perfusion and an in vitro method (Ussing chamber model). The low-Ca2+ diet stimulated net Ca2+ flux in the ileum twofold, associated with a twofold increase of the mucosal-to-serosal Ca2+ flux in both models. This effect was observed in the absence of concomitant changes in Na+ or water flux in the in situ model or mannitol flux in the in vitro model, excluding the participation of the paracellular pathway in Ca2+ transport. Thus only cellular Ca2+ flux was stimulated. These data suggest that the ileum plays a major role in the adaptation to low dietary Ca2+. Whereas under physiological conditions with usual Ca2+ intakes the transcellular pathway of Ca2+ transport is negligible, it becomes of major importance in the case of Ca2+ deficiency, at least under the present conditions of severe Ca2+ deprivation.
Auchère
D
D
Laboratoire de Physiologie, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris XI, 92290 Châtenay-Malabry, France.
Tardivel
S
S
Gounelle
J C
JC
Drüeke
T
T
Lacour
B
B
D000818:Animals; D001834:Body Water / Q000378:metabolism; D002118:Calcium / Q000172:deficiency / Q000378:metabolism*; D002136:Calcium, Dietary; D007082:Ileum / Q000502:physiology*; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D009130:Muscle, Smooth / Q000502:physiology; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism
D002136:Calcium, Dietary; D012964:Sodium; D002118:Calcium