Effect of calcium and mineral waters on oleic-acid uptake by isolated hamster enterocytes

The effect of calcium upon the uptake of oleic acid solubilized with 10 mM taurocholate was investigated using an in vitro model of isolated enterocytes. The addition of Ca2+ to the incubation medium (Hanks' medium) led to a decrease in oleic-acid uptake. This uptake inhibition was dependent on both the amount of Ca2+ and the fatty-acid concentration, since the inhibitory effect was significant for 10 microM but not 100 microM oleic acid. The determination of the monomeric activity of oleic acid indicated that the decrease in fatty-acid uptake was not linked to the formation of insoluble calcium soaps. The replacement of Hank's medium by several mineral waters containing between 0.3 and 11.7 mM Ca2+ significantly reduced the uptake of both 10 and 100 microM oleic-acid. The ionic composition of these waters was correlated with the decrease of initial rate of oleic acid uptake, but Ca2+ and other ions could interfere by synergetic effects with the fatty-acid-absorption mechanism. It is concluded that the ion-induced inhibition of oleic-acid uptake is not due to the formation of insoluble soaps but rather to a direct effect on the fatty-acid transport in membranes. Whether the fatty-acid binding protein in the plasma membrane is involved in the effect of Ca2+ on fatty-acid transport remains to be established.