Transport of calcium across caco-2 cells in the presence of inositol hexakisphosphate

The Caco-2 enterocyte cell model was used to determine whether low concentrations of inositol hexakisphosphate (InsP6, phytate) may enhance calcium absorption, as was recently reported for several nonintestinal types of mammalian cells. Three-week-old Caco-2 cell layers grown in tissue culture plates with or without cell culture inserts were incubated with [45Ca]Cl2 to examine calcium transport or uptake, respectively. No increases in calcium uptake were observed in the presence of micromolar levels of InsP6, whereas millimolar levels of InsP6 gave incongruous results depending on the calcium concentration. The fractional apical-to-basolateral calcium transport was significantly inhibited (P < .05) by InsP6 levels of 100 μmol/L and above, but the total molar amount of calcium transported still increased with increasing concentrations of calcium. It was concluded that InsP6 cannot enhance calcium absorption by Caco-2 cells, Caco-2 cell transport is a better indicator of calcium availability than uptake, and higher consumption of calcium may overcome the inhibition of InsP6.