Auchère D, Tardivel S, Gounelle J C, Drüeke T, Lacour B
Laboratoire de Physiologie, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris XI, 92290 Châtenay-Malabry, France.
Am J Physiol. 1998 Nov;275(5):G951-6. doi: 10.1152/ajpgi.1998.275.5.G951.
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.
本研究旨在确定细胞途径和细胞旁途径在回肠钙转运中的各自作用。两组大鼠分别给予正常钙饮食（1.0%）或低钙饮食（0.02%），持续14天。采用原位连续肠腔灌注法和体外法（尤斯灌流室模型）测定回肠钙吸收。低钙饮食使回肠净钙通量增加了两倍，在两种模型中，黏膜到浆膜的钙通量也相应增加了两倍。在原位模型中，钠通量或水通量以及体外模型中的甘露醇通量均未伴随变化，这排除了细胞旁途径参与钙转运的可能性。因此，只有细胞钙通量受到刺激。这些数据表明，回肠在适应低钙饮食方面起主要作用。在生理条件下，当钙摄入量正常时，钙转运的跨细胞途径可忽略不计，但在钙缺乏的情况下，至少在目前严重钙缺乏的条件下，它变得至关重要。
