Ethanolamine and choline transport in cultured bovine aortic endothelial cells

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Abstract
The transport of the polar head groups, ethanolamine and choline, was examined in cultured bovine aortic endothelial cells. Both ethanolamine and choline are taken up by high- and low-affinity systems. The K'm and V'max for the Na+-dependent, high-affinity ethanolamine and choline transport system are 3.0 and 3.0 μM and 5.4 and 7.3 pmol/mg protein/min, respectively. Ethanolamine and choline competitively influence one another's transport as the presence of 50 μM ethanolamine increases the K'm but not the V'max of choline uptake. Likewise, 50 μM choline increases the K'm but not the V'max of ethanolamine transport. The concentration of ethanolamine that inhibits maximal velocity of 5 μM choline by 50% is 9.7 μM, while 12 μM choline inhibits 5 μM ethanolamine maximal velocity by 50%. Uptake of both head groups is only partially Na+-dependent and is inhibited similarly by 2-methylethanolamine and 2,2-dimethyl-ethanolamine at all concentrations examined. Hemicholinium-3, a classic inhibitor of high-affinity, Na+-dependent choline transport, reduces both ethanolamine and choline accumulation in a concentration-dependent fashion, but has a greater effect on choline transport at higher concentrations. The major portion of these data is consistent with our hypothesis that the uptake of physiological concentrations of ethanolamine and choline may occur through the same transport system. However, the results of the effect of hemicholinium-3 and the extent of Na+-dependency of choline and ethanolamine uptake could be interpreted as meaning that separate transport systems for choline and ethanolamine exist which cross react or that a single transport system exists which has separate active sites for the two compounds.