Luminal calcium concentration controls intestinal calcium absorption by modification of intestinal alkaline phosphatase activity

BRUN LR; BRANCE ML; RIGALLI A

BRITISH JOURNAL OF NUTRITION

CAMBRIDGE UNIV PRESS

Año: 2012 vol. 108 p. 229 - 233

0007-1145

Intestinal alkaline phosphatase (IAP) is a brush border phosphomonoesterase. Its location suggests an involvement in the uptake of nutrients but its role has not been defined yet. IAP expression parallels that of other proteins involved in calcium (Ca) absorption under vitamin D stimulation. Experiments carried out in vitro with purified IAP have demonstrated interaction between Ca and IAP. The gut is prepared to face different levels of Ca intake along time, but high Ca intake in a situation of low Ca diet along time would cause high entry of Ca to the enterocyte. The presence of a mechanism to block Ca entry and avoid possible adverse effects is thus predictable. Thus, in the present work, Sprague Dawley rats fed with different amounts of Ca in the diet (0.2g%, 1g% and 2g%), and percentage of Ca absorption (%Ca) in the presence and absence of L-phenylalanine (Phe) was calculated. The presence of Phe caused a significant increase in %Ca (52.3%±6.5 in the presence of Phe vs 31.1%±8.9 in the absence of Phe, regardless of the amount of Ca intake; Paired t test, p=0.02). When data were analyzed in function of Ca intake, a significant difference was found only in the group with low Ca intake (Paired t test, p=0.03). Additionally, IAP activity increased significantly (ANOVA, p0.05) as Ca concentrations increased in the duodenal lumen. This study provides in vivo evidence that luminal Ca concentration increases the activity of IAP and simultaneously decreases %Ca, acting as a minute-to-minute regulation mechanism of Ca entry.