Calcium uptake by duodenal epithelial cells is increased during lactation

It is known that duodenal absorption of calcium is increased during lactation, and, more specifically, it has been shown that duodenal active transport of calcium is increased. The energy-requiring step for this active transport process is thought to occur at the basolateral membrane of the duodenal epithelial cells, where calcium is pumped from the cell into the extracellular fluid. The present experiments were carried out to determine whether calcium uptake into duodenal epithelial cells is also altered during lactation. Uptake of 45Ca into isolated duodenal epithelial cells from lactating animals showed markedly enhanced calcium uptake when compared with cells from control animals. Uptake was calcium concentration dependent for both groups. Since duodenal epithelial cells are known to contain increased calbindin9k, a calcium-binding protein, during lactation, calcium uptake was also measured in cells that were preincubated in medium containing calcium. In these experiments, the total 45Ca uptake was reduced, but the difference between lactating and control remained. These experiments show that the uptake of calcium into duodenal epithelial cells is among the components of the transcellular calcium transport process which is enhanced during lactation.