[3H]L-arginine transport and nitric oxide synthase activity in foetal hypothalamic cultures

[3H]L-arginine uptake and the conversion of [3H]L-arginine to [3H]citrulline were characterized in foetal hypothalamic cultures. [3H]L-arginine uptake was reduced by L-ornithine (10 microM-1 mM), high extracellular K+ (56 mM), L-glutamate (100 microM) and removal of extracellular Ca2+, but was increased by the nitric oxide synthase inhibitor, Nw-nitro-L-arginine benzyl ester (L-NABE; 1 mM). [3H]citrulline formation was inhibited by L-NABE (1 mM), increased by high extracellular K+ (56 mM) and unaffected by L-glutamate (100 microM). Removal of extracellular Ca2+ reduced [3H]citrulline formation by mixed (neurones and glia) and neurone-enriched cultures but not by glial-enriched cells. The results suggest that [3H]L-arginine uptake into hypothalamic cultures is mediated by the system y+ transporter and is dependent on extracellular Ca2+. [3H]citrulline production in hypothalamic neuronal, but not glial, cells is also dependent on extracellular Ca2+.