Neutral amino acid transport properties of cerebral endothelial cells in vitro.

An A and L system of neutral amino acid transport has been demonstrated previously in cerebral microvessels in vivo and in isolated microvessels in vitro. This report describes the neutral amino acid transport properties of cultured cerebral endothelial cells and investigates the influence of astroglia on the transport process. These studies confirm the presence of a sodium-dependent A-system and a sodium-independent L-system of neutral amino acid transport in cultured cerebral endothelial cells. The A-system transport is slower than L-system transport and each is variably inhibited by other amino acids. Transport is enhanced in log phase cells as compared to stationary phase contact-inhibited cells. Contact with glial cells or exposure to glial-conditioned media enhances neutral amino acid transport. These in vitro studies indicate that the A- and L-systems of neutral amino acid transport are in a dynamic state and are influenced by the phase of cell growth and contact with astroglia.