TRANSPORT OF 2-AMINOISOBUTYRIC ACID IN CULTURED ENDOTHELIAL-CELLS

Conflicting reports exist concerning the presence of a Na+-coupled amino acid transport system in cultured endothelial cells. We have employed a non-metabolizable analog, 2-aminoisobutyric acid (AIB), to investigate the activity of Na+-dependent amino acid transport in cultured human umbilical vein endothelial cells (HUVEC). We found a pronounced saturable, Na+-dependent component of AIB uptake in 'fresh' (non-starved) HUVEC. The Na+-dependent component accounted for 78% of total AIB uptake with a high sensitivity to external Na+. The accumulation of AIB was inhibited by ouabain preincubation, consistent with the energetics of Na+-coupled transport. Amiloride, an epithelial Na+ channel blocker, also inhibited AIB transport at high concentration. The results strongly support the presence of a Na+-coupled transport system of amino acid in HUVEC.