Dietary calcium deficiency increases Ca2+ uptake and Ca2+ extrusion mechanisms in chick enterocytes
2004
Centeno, V.A. | Diaz de Barboza, G.E. | Marchionatti, A.M. | Alisio, A.E. | Dallorso, M.E. | Nasif, R. | Tolosa de Talamoni, N.G.
Ca2+ uptake and Ca2+ extrusion mechanisms were studied in enterocytes with different degree of differentiation from chicks adapted to a low Ca2+ diet as compared to animals fed a normal diet. Chicks adapted to a low Ca2+ diet presented hypocalcemia, hypophosphatemia and increased serum 1,25(OH)2D3 and Ca2+ absorption. Low Ca2+ diet increased the alkaline phosphatase (AP) activity, independently of the cellular maturation, but it did not alter γ-glutamyl-transpeptidase activity. Ca2+ uptake, Ca2+-ATPase and Na+/Ca2+ exchanger activities and expressions were increased by the mineral-deficient diet either in mature or immature enterocytes. Western blots analysis showS that vitamin D receptor (VDR) expression was much higher in crypt cells than in mature cells. Low Ca2+ diet decreased the number of vitamin D receptor units in both kinds of cells. In conclusion, changes in Ca2+ uptake and Ca2+ extrusion mechanisms in the enterocytes by a low Ca2+ diet appear to be a result of enhanced serum levels of 1,25(OH)2D3, which would promote cellular differentiation producing cells more efficient to express vitamin D dependent genes required for Ca2+ absorption.
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