HOMOCYSTEINE UPTAKE BY HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS IN CULTURE

The characteristics of the uptake of l-homocysteine by cultures of human umbilical vein endothelial cells have been examined. Uptake occurred by Na+-dependent and Na+-independent systems, but was essentially independent of the pH of the uptake medium. The Na+-independent system corresponded to system L, being totally inhibited by the presence of β-2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH) a system L analogue. It was concluded on the basis of starvation experiments coupled with failure to detect any inhibition in the presence of 2-methylaminoisobutyric acid (MeAIB), a system A analogue, that the Na+-dependent uptake was wholly accounted for by system ASC. The kinetic properties of systems L and ASC were determined by omitting Na+ from the uptake medium and incorporating BCH in the medium, respectively. It has been concluded on the basis of the inhibitory effects of a number of amino acids that uptake of homocysteine occurs by those systems which transport cysteine. © 1990.